diff --git a/AGENTS.md b/AGENTS.md
index 54e0130f..28a1b548 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -163,17 +163,23 @@ fresh-vs-reused results and complete reset/reentrancy gates. Slice I2 is also
 complete: immutable physics/containment BSP, polygon, Setup, bounds, and
 EnvCell-topology records preserve source float bits and ordering across
 synthetic corruption gates and representative installed DATs without changing
-production traversal.
+production traversal. Slice I3 is complete: bake-tool 4 appends typed GfxObj,
+Setup, CellStruct, and EnvCell-topology collision payloads; the collision
+interface shares the render package's single mmap. Two complete
+29,908,271,024-byte bakes produced 2,232,170 typed keys, zero failures, and the
+same SHA-256 across 16 and 7 workers. Corruption, cancellation, installed
+package, Release build, and 8,371-test / 5-skip gates pass.
 Slice H's retained UI/frame, bounded-light, and pooled/borrowed/direct network
 work is complete; the exact seven-checkpoint connected lifecycle/reconnect gate
-passes. Slice I is active at I3 from
+passes. Slice I is active at I4 from
 `docs/plans/2026-07-25-modern-runtime-slice-i.md`. The exact G4 visual rollback
 is `git revert ef1d263337997bb030eadb7b8e71d73dc659907a`; do not revert G3 or
 the portal-warmup corrections. Evidence:
 `docs/research/2026-07-25-slice-h-closeout.md` and
 `docs/research/2026-07-25-slice-g5-production-profile.md` and
 `docs/research/2026-07-25-slice-i1-transition-scratch.md` and
-`docs/research/2026-07-25-slice-i2-flat-collision-schema.md`.
+`docs/research/2026-07-25-slice-i2-flat-collision-schema.md` and
+`docs/research/2026-07-25-slice-i3-prepared-collision-package.md`.
 
 **Structural prerequisite before new M4 subsystem work:** all eight
 behavior-preserving `GameWindow` decomposition slices and the automated
diff --git a/CLAUDE.md b/CLAUDE.md
index 9a5fbe9e..66ac413f 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -161,17 +161,23 @@ fresh-vs-reused results and complete reset/reentrancy gates. Slice I2 is also
 complete: immutable physics/containment BSP, polygon, Setup, bounds, and
 EnvCell-topology records preserve source float bits and ordering across
 synthetic corruption gates and representative installed DATs without changing
-production traversal.
+production traversal. Slice I3 is complete: bake-tool 4 appends typed GfxObj,
+Setup, CellStruct, and EnvCell-topology collision payloads; the collision
+interface shares the render package's single mmap. Two complete
+29,908,271,024-byte bakes produced 2,232,170 typed keys, zero failures, and the
+same SHA-256 across 16 and 7 workers. Corruption, cancellation, installed
+package, Release build, and 8,371-test / 5-skip gates pass.
 Slice H's retained UI/frame, bounded-light, and pooled/borrowed/direct network
 work is complete; the exact seven-checkpoint connected lifecycle/reconnect gate
-passes. Slice I is active at I3 from
+passes. Slice I is active at I4 from
 `docs/plans/2026-07-25-modern-runtime-slice-i.md`. The exact G4 visual rollback
 is `git revert ef1d263337997bb030eadb7b8e71d73dc659907a`; do not revert G3 or
 the portal-warmup corrections. Evidence:
 `docs/research/2026-07-25-slice-h-closeout.md` and
 `docs/research/2026-07-25-slice-g5-production-profile.md` and
 `docs/research/2026-07-25-slice-i1-transition-scratch.md` and
-`docs/research/2026-07-25-slice-i2-flat-collision-schema.md`.
+`docs/research/2026-07-25-slice-i2-flat-collision-schema.md` and
+`docs/research/2026-07-25-slice-i3-prepared-collision-package.md`.
 
 **Structural prerequisite before new M4 subsystem work:** all eight
 behavior-preserving `GameWindow` decomposition slices and the automated
diff --git a/docs/architecture/acdream-architecture.md b/docs/architecture/acdream-architecture.md
index 07736112..4bba7034 100644
--- a/docs/architecture/acdream-architecture.md
+++ b/docs/architecture/acdream-architecture.md
@@ -173,6 +173,8 @@ src/
       TerrainSurface.cs       -> triangle-aware terrain contact (done)
       BSPQuery.cs             -> partial retail BSP dispatcher (active in L.2)
       TransitionTypes.cs      -> SpherePath / CollisionInfo / transition helpers (active in L.2)
+      FlatCollisionAssets.cs  -> immutable array/index collision schema (Slice I2)
+      FlatCollisionAssetBuilder.cs -> deterministic DAT graph preparation (Slice I2/I3)
       PhysicsDataCache.cs     -> GfxObj / Setup / CellStruct collision data (done, active)
       ShadowObjectRegistry.cs -> broadphase for nearby physics objects (active)
       PhysicsEngine.cs        -> ResolveWithTransition active player path
diff --git a/docs/architecture/worldbuilder-inventory.md b/docs/architecture/worldbuilder-inventory.md
index 71133877..95636b56 100644
--- a/docs/architecture/worldbuilder-inventory.md
+++ b/docs/architecture/worldbuilder-inventory.md
@@ -120,8 +120,9 @@ EnvCell, Surface, palette, and texture graphs during portals. The validated
 machine-local `acdream.pak` is opened through Content's
 `IPreparedAssetSource`; typed GfxObj and EnvCell requests deserialize immutable
 `ObjectMeshData` while retaining the existing App worker, staging, render-thread
-upload, cache, ownership, and shutdown contracts. The format-1/bake-tool-3
-payload persists exact batch translucency so App does not reconstruct a
+upload, cache, ownership, and shutdown contracts. The original
+format-1/bake-tool-3 render payload persists exact batch translucency so App
+does not reconstruct a
 `GfxObjMesh` for metadata. Setup activation uses the package TOC as an explicit
 type-presence index before reading valid Setup records through the bounded DAT
 cache. `DatPreparedAssetSource` and `MeshExtractor` remain explicit
@@ -131,6 +132,18 @@ bake/equivalence/UI-Studio tools, not a production fallback. Portal → HighRes
 installed-DAT gates are recorded in
 `docs/research/2026-07-24-slice-c-prepared-asset-cutover-report.md`.
 
+**Slice I3 prepared collision extension (2026-07-25).** The package remains
+format 1 and retains mesh type values 1–3; bake-tool 4 appends typed GfxObj,
+Setup, CellStruct, and EnvCell-topology collision payloads. Core owns the
+immutable flat records and deterministic raw-DAT flattener. Content owns the
+strict little-endian codec and `IPreparedCollisionSource`.
+`PakPreparedAssetSource` implements the render and collision interfaces over
+one mmap; it does not create a second DAT reader or mapping. CellStruct
+payloads alias only after exact serialized-byte comparison, while each
+EnvCell topology remains independently keyed. Production traversal is still
+the parsed graph oracle until Slice I6. Full-catalog evidence:
+`docs/research/2026-07-25-slice-i3-prepared-collision-package.md`.
+
 **Retail VFX hook compatibility seam (2026-07-14).** Chorizite.DatReaderWriter
 2.1.7 models `CreateBlockingParticleHook` as the common hook header only, while
 retail inherits the complete `CreateParticleHook` payload. The narrow readers in
diff --git a/docs/plans/2026-04-11-roadmap.md b/docs/plans/2026-04-11-roadmap.md
index 48133478..5184d580 100644
--- a/docs/plans/2026-04-11-roadmap.md
+++ b/docs/plans/2026-04-11-roadmap.md
@@ -1660,7 +1660,7 @@ port in any phase — no separate listing here.
 > `git revert ef1d263337997bb030eadb7b8e71d73dc659907a`. Slice H is complete:
 > retained UI/frame work, exact bounded light selection, and
 > pooled/borrowed/direct network I/O pass 8,292 Release tests / 5 skips and the
-> connected lifecycle/reconnect gate. Slice I is active at I3 from
+> connected lifecycle/reconnect gate. Slice I is active at I4 from
 > [its detailed plan](2026-07-25-modern-runtime-slice-i.md).
 
 **Spec:** `docs/superpowers/specs/2026-07-05-modern-pipeline-design.md` (the
@@ -1685,11 +1685,11 @@ hitch and follows.
 | MP1a | `AcDream.Content` extraction (GL-free MeshExtractor + boundary records out of App) | ✅ SHIPPED 2026-07-05 — user-gated (renders identical, zero tripwires, perf-neutral); 8 commits `651d041e`..`b0758d77` |
 | MP1b | Pak format + `acdream-bake` CLI + mmap `PakReader` + equivalence/full-scale gate | ✅ **SHIPPED 2026-07-24** — 729,888 EnvCell keys → 17,117 unique geometries + 712,771 aliases (42.6×), 751,141 total keys / 38,370 physical blobs, zero failures, 28,192.4 MiB, 81.4 s validated atomic publish; full-DAT gate also corrected a real collision in WB's legacy geometry hash. [Report](../research/2026-07-24-slice-b-full-bake-report.md) |
 | **MP-Alloc (safe batch)** | Reuse per-frame buffers: anim pose, particle draw-list, interior partition, animatedIds/drawableCells sets | ✅ SHIPPED + USER-GATED 2026-07-05 — dense-town frame-time spikes 20–87ms → 6–10ms, alloc spikes (30–75MB single-frame) eliminated, gen2 GC 5–11/window → ~0; user confirms FPS steady. 4 commits `b8c05e2b`..`91afea24` |
-| MP-Alloc (hard sites) | EnvCell settled-camera rebuild gate + physics `Transition` reuse | 🟡 Physics half SHIPPED 2026-07-25 — retail-shaped reset-complete transition/query scratch is bit-identical and 0 B/resolve across five profiles; immutable flat collision storage is defined and package integration continues in Slice I3. |
+| MP-Alloc (hard sites) | EnvCell settled-camera rebuild gate + physics `Transition` reuse | 🟡 Physics half SHIPPED 2026-07-25 — retail-shaped reset-complete transition/query scratch is bit-identical and 0 B/resolve across five profiles; immutable flat collision storage and its complete deterministic prepared package are shipped; traversal differential work continues in Slice I4. |
 | MP1c | Streaming cutover to pak + hitch gate | ✅ **SHIPPED 2026-07-24** — typed package-only production source, explicit Setup probes, non-allocating Portal-first lookup, exact translucency metadata, and ordered teardown; capped/uncapped/dense physical routes + user visual gate pass. Uncapped CPU p99 7.825→6.496 ms, GPU p99 3.406→2.706 ms, portal frame max 202.9→39.9 MiB, process allocation −41.8%, zero invalid Setup probes. [Report](../research/2026-07-24-slice-c-prepared-asset-cutover-report.md) |
 | MP2 | Retail particle distance/cell-view degradation: DAT-authored range, exact infinite/finite off-view update branches, emitter-first render scan, user-requested 2× default range | ✅ SHIPPED 2026-07-17 — Aerlinthe hotspot `0x32000223` resolves to retail 64m and defaults to 128m; landscape/entity streaming distance unchanged |
 | MP3 | Arch ECS render world + delta submission (the 300-FPS lever) | ⚪ — note: does NOT fix the steady-state GC churn (that's MP-Alloc); MP3 is the draw-submission throughput lever |
-| MP4 | Zero-alloc frame loop + flat physics data (residual, post-MP-Alloc) | 🟡 ACTIVE — Slice I1 zero-allocation transition scratch and I2 immutable flat collision schema shipped; I3 package serialization/bake is active. |
+| MP4 | Zero-alloc frame loop + flat physics data (residual, post-MP-Alloc) | 🟡 ACTIVE — Slice I1 zero-allocation transition scratch, I2 immutable schema, and I3 complete deterministic collision package shipped; I4 flat traversal shadow implementation is active. |
 | MP5 | Job-system parallelism | ⚪ stretch, evidence-gated |
 
 ---
diff --git a/docs/plans/2026-05-12-milestones.md b/docs/plans/2026-05-12-milestones.md
index 8b59484e..085caaad 100644
--- a/docs/plans/2026-05-12-milestones.md
+++ b/docs/plans/2026-05-12-milestones.md
@@ -123,9 +123,13 @@ deterministic immutable physics/containment BSP, polygon, Setup, bounds, and
 EnvCell-topology records without cutting traversal over. Synthetic corruption
 gates and representative installed-DAT source identity pass bit-for-bit. The
 complete I2 Release gate is 3,826 App tests / 3 skips and 8,355 solution tests
-/ 5 skips.
+/ 5 skips. I3 appends four collision package types and a separate typed
+prepared-collision interface over the existing single mmap. Two complete
+29,908,271,024-byte bakes contain 2,232,170 keys with zero failures and the
+same SHA-256 across different worker counts; cancellation/corruption gates and
+8,371 solution tests / 5 skips pass.
 Slice H is complete: retained UI/frame work, exact bounded light selection,
-and pooled/borrowed/direct network I/O pass. Slice I is active at I3 under
+and pooled/borrowed/direct network I/O pass. Slice I is active at I4 under
 [`2026-07-25-modern-runtime-slice-i.md`](2026-07-25-modern-runtime-slice-i.md).
 The historical exact G4 visual rollback remains
 `git revert ef1d263337997bb030eadb7b8e71d73dc659907a`.
diff --git a/docs/plans/2026-07-24-modern-runtime-architecture.md b/docs/plans/2026-07-24-modern-runtime-architecture.md
index cb5455de..87a1ec2a 100644
--- a/docs/plans/2026-07-24-modern-runtime-architecture.md
+++ b/docs/plans/2026-07-24-modern-runtime-architecture.md
@@ -2,8 +2,8 @@
 
 **Date:** 2026-07-24
 
-**Status:** Slices A–H and I0–I2 are complete. Slices F–L were explicitly
-approved 2026-07-24; Slice I3 is active.
+**Status:** Slices A–H and I0–I3 are complete. Slices F–L were explicitly
+approved 2026-07-24; Slice I4 is active.
 
 **Scope:** Reconcile and sequence the existing Modern Pipeline (`MP`) and
 Linux/headless (`LH`) tracks using the 2026-07-24 connected performance audit.
@@ -1200,8 +1200,10 @@ grounded walkable-publication profiles each measure 0 B/resolve, while
 fresh-vs-reused output and body state remain bit-identical. I2 now supplies
 validated immutable flat collision records: synthetic and installed-DAT
 source identity, exact float bits, deterministic pre-order, and corruption
-tripwires pass without changing production traversal. I3 package
-serialization and complete-catalog baking are the current execution point.
+tripwires pass without changing production traversal. I3 now packages all
+flat collision/topology records through a shared typed mmap source: two
+complete 2,232,170-key bakes are byte-identical with zero failures. I4 flat
+traversal shadow implementation is the current execution point.
 Evidence:
 [`../research/2026-07-25-slice-g5-production-profile.md`](../research/2026-07-25-slice-g5-production-profile.md)
 and
@@ -1209,6 +1211,8 @@ and
 and
 [`../research/2026-07-25-slice-i2-flat-collision-schema.md`](../research/2026-07-25-slice-i2-flat-collision-schema.md)
 and
+[`../research/2026-07-25-slice-i3-prepared-collision-package.md`](../research/2026-07-25-slice-i3-prepared-collision-package.md)
+and
 [`2026-07-25-modern-runtime-slice-i.md`](2026-07-25-modern-runtime-slice-i.md).
 
 The intended order is therefore:
@@ -1222,7 +1226,7 @@ honest metrics + committed baselines        (A — exit criteria block C)
   -> incremental render scene               (F)
   -> delta GPU submission                   (G)
   -> residual frame cleanup                 (H-a, H-b, H-c)
-  -> flat collision assets                  (I — CURRENT at I3)
+  -> flat collision assets                  (I — CURRENT at I4)
   -> presentation-independent runtime       (J — §0.3 authorization)
   -> Linux/headless/multi-session           (K)
   -> evidence-gated GPU jobs                (L)
diff --git a/docs/plans/2026-07-25-modern-runtime-slice-i.md b/docs/plans/2026-07-25-modern-runtime-slice-i.md
index e3ac18df..6d61b228 100644
--- a/docs/plans/2026-07-25-modern-runtime-slice-i.md
+++ b/docs/plans/2026-07-25-modern-runtime-slice-i.md
@@ -1,7 +1,8 @@
 # Modern runtime Slice I — flat collision assets and zero-allocation physics
 
-**Status:** I0–I2 COMPLETE — retail oracle, zero-allocation transition
-scratch, and deterministic immutable collision records fixed; I3 active
+**Status:** I0–I3 COMPLETE — retail oracle, zero-allocation transition
+scratch, deterministic immutable collision records, and complete prepared
+package fixed; I4 active
 **Parent:** `2026-07-24-modern-runtime-architecture.md`, Slice I
 **Purpose:** remove parsed DAT object graphs and steady collision allocations
 without changing one retail collision decision, float, comparison, or traversal
@@ -176,7 +177,12 @@ Evidence:
 
 Gate: two independent bakes are byte-identical; every collision key required
 by the canonical route is present; a failed/cancelled bake cannot replace the
-last good pak.
+last good pak. **PASSED 2026-07-25:** two complete 29,908,271,024-byte bakes
+with different worker counts produced the same SHA-256 and 2,232,170 typed
+keys with zero failures. Strict serialization/corruption/cancellation gates,
+representative installed-package reads, Release build, and 8,371 solution
+tests / 5 skips pass. Production traversal remains graph-only. Evidence:
+[`../research/2026-07-25-slice-i3-prepared-collision-package.md`](../research/2026-07-25-slice-i3-prepared-collision-package.md).
 
 ### I4 — flat traversal shadow implementation
 
diff --git a/docs/research/2026-07-25-slice-i3-prepared-collision-package.md b/docs/research/2026-07-25-slice-i3-prepared-collision-package.md
new file mode 100644
index 00000000..5da806c4
--- /dev/null
+++ b/docs/research/2026-07-25-slice-i3-prepared-collision-package.md
@@ -0,0 +1,97 @@
+# Slice I3 — prepared flat-collision package
+
+**Date:** 2026-07-25
+**Scope:** Modern Runtime Slice I3 only
+**Behavioral boundary:** storage, serialization, bake, and prepared lookup;
+production collision traversal remains on the parsed-DAT graph oracle.
+
+## Result
+
+The existing format-1 `acdream.pak` now carries four appended asset types:
+
+| Numeric type | Payload |
+|---:|---|
+| 4 | GfxObj collision BSP, polygon table, bounding sphere, and visual bounds |
+| 5 | Setup cylinders, spheres, and movement dimensions |
+| 6 | reusable CellStruct physics BSP, containment BSP, and portal polygons |
+| 7 | independently keyed EnvCell portals, visibility, and `seen_outside` |
+
+The existing mesh type values 1–3 did not change. Bake-tool identity advanced
+from 3 to 4; the package binary container remains format 1.
+
+`FlatCollisionAssetSerializer` is a strict little-endian codec. It:
+
+- writes every `float` through `SingleToInt32Bits`;
+- retains node, polygon, vertex, Setup-shape, portal, and visible-cell order;
+- checks counts before allocation and validates combined byte requirements;
+- checks cancellation during large rows;
+- rejects wrong payload kinds, unsupported schema versions, non-zero reserved
+  bits, invalid enum/tree/range contracts, truncation, and trailing bytes;
+- remains behind the package entry CRC, so a CRC or structural fault marks
+  only that typed entry corrupt.
+
+`IPreparedCollisionSource` is separate from the render-only
+`IPreparedAssetSource` API. `PakPreparedAssetSource` implements both over the
+same `PakReader` and therefore maps the 29.9 GB immutable package once, not
+once per subsystem. Render and collision counters are independent.
+
+CellStruct collision geometry is addressed by every EnvCell source key. The
+bake emits ordinary TOC aliases within the same source group and across groups
+only after comparing the complete serialized payload bytes. Per-cell topology
+is always written under its own key and is never inferred from shared render
+geometry.
+
+## Complete installed-DAT bake
+
+Two independent full bakes used 16 and 7 workers:
+
+| Metric | Result |
+|---|---:|
+| GfxObj mesh keys | 15,318 |
+| Setup mesh keys | 5,935 |
+| EnvCell mesh keys | 729,888 |
+| GfxObj collision keys | 15,318 |
+| Setup collision keys | 5,935 |
+| CellStruct collision keys | 729,888 |
+| EnvCell topology keys | 729,888 |
+| Total typed keys | 2,232,170 |
+| Physical blobs | 781,196 |
+| Failures | 0 |
+| File bytes | 29,908,271,024 |
+| SHA-256 | `FEE8595D512DCB119C98B3D9911CDF9A905C97B624BCB826CEAF8DFD3F67269C` |
+
+Both complete files have identical length and SHA-256. Exact-byte
+deduplication produced:
+
+- 9,363 physical GfxObj collision blobs behind 15,318 keys;
+- 979 physical Setup collision blobs behind 5,935 keys;
+- 2,596 physical CellStruct collision blobs behind 729,888 keys.
+
+The 16-worker bake completed and validated in 107.5 seconds; the 7-worker bake
+completed and validated in 80.5 seconds. Peak bake-process memory was
+4.43–4.89 GB working set and 3.81–4.21 GB private. This is offline extraction
+state and is not mapped as committed client memory; the production source
+memory-maps the immutable file and pages only accessed ranges.
+
+The validated bake-tool-4 package was installed at the machine-local DAT
+location for subsequent Slice I gates.
+
+## Verification
+
+- strict codec round-trip and exact-float-bit tests for all four payloads;
+- every truncation of a representative payload rejected;
+- wrong-kind, negative/impossible count, trailing-byte, CRC, and valid-CRC
+  structural-corruption tests;
+- concurrent prepared reads and separate render/collision accounting;
+- raw-DAT versus current cached-source preparation on representative installed
+  GfxObjs, Setups, and EnvCells;
+- filtered 1/8- and 8/3-worker bake equivalence and exact alias tests;
+- complete installed package reads for representative GfxObj, Setup,
+  CellStruct, and EnvCell topology keys;
+- failed validation and timed cancellation preserve the last published file;
+- Release build: zero warnings;
+- complete Release suite: 8,371 passed / 5 skipped.
+
+No divergence-register row changes: no gameplay decision or traversal route
+changed. Slice I4 adds the flat traversal referee while the graph path remains
+authoritative.
diff --git a/src/AcDream.Bake/AcDream.Bake.csproj b/src/AcDream.Bake/AcDream.Bake.csproj
index 263db624..9b04f741 100644
--- a/src/AcDream.Bake/AcDream.Bake.csproj
+++ b/src/AcDream.Bake/AcDream.Bake.csproj
@@ -10,6 +10,10 @@
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
   </PropertyGroup>
 
+  <ItemGroup>
+    <InternalsVisibleTo Include="AcDream.Bake.Tests" />
+  </ItemGroup>
+
   <ItemGroup>
     <!-- NO Silk.NET / GL packages here — ever. acdream-bake is an offline CLI
          that drives the GL-free AcDream.Content.MeshExtractor; it must not
diff --git a/src/AcDream.Bake/BakeArtifactValidator.cs b/src/AcDream.Bake/BakeArtifactValidator.cs
index ceb23edd..b35e6cf6 100644
--- a/src/AcDream.Bake/BakeArtifactValidator.cs
+++ b/src/AcDream.Bake/BakeArtifactValidator.cs
@@ -8,7 +8,8 @@ public static class BakeArtifactValidator
     public static void Validate(
         string path,
         in PakHeader expectedHeader,
-        int expectedTocCount)
+        int expectedTocCount,
+        IReadOnlyDictionary<PakAssetType, int>? expectedTypeCounts = null)
     {
         using var reader = new PakReader(path);
         var actual = reader.Header;
@@ -35,5 +36,18 @@ public static class BakeArtifactValidator
                 $"{expectedTocCount}");
 
         reader.ValidateTocStructure();
+        if (expectedTypeCounts is null)
+            return;
+
+        foreach ((PakAssetType type, int expectedCount) in expectedTypeCounts)
+        {
+            int actualCount = reader.CountEntries(type);
+            if (actualCount != expectedCount)
+            {
+                throw new InvalidDataException(
+                    $"bake catalog type {type} contains {actualCount} keys; " +
+                    $"expected {expectedCount}");
+            }
+        }
     }
 }
diff --git a/src/AcDream.Bake/BakeRunner.cs b/src/AcDream.Bake/BakeRunner.cs
index f2346bc4..9ea6f1bb 100644
--- a/src/AcDream.Bake/BakeRunner.cs
+++ b/src/AcDream.Bake/BakeRunner.cs
@@ -3,9 +3,12 @@ using System.Diagnostics;
 using System.Numerics;
 using AcDream.Content;
 using AcDream.Content.Pak;
+using AcDream.Core.Physics;
 using DatReaderWriter;
 using DatReaderWriter.DBObjs;
+using DatReaderWriter.Enums;
 using DatReaderWriter.Options;
+using DatReaderWriter.Types;
 using DatEnvironment = DatReaderWriter.DBObjs.Environment;
 
 namespace AcDream.Bake;
@@ -30,6 +33,16 @@ public sealed record BakeReport
     public required int EnvCellKeys { get; init; }
     public required int UniqueEnvCellGeometries { get; init; }
     public required int EnvCellAliases { get; init; }
+    public required int GfxObjCollisionKeys { get; init; }
+    public required int UniqueGfxObjCollisions { get; init; }
+    public required int GfxObjCollisionAliases { get; init; }
+    public required int SetupCollisionKeys { get; init; }
+    public required int UniqueSetupCollisions { get; init; }
+    public required int SetupCollisionAliases { get; init; }
+    public required int CellStructureCollisionKeys { get; init; }
+    public required int UniqueCellStructureCollisions { get; init; }
+    public required int CellStructureCollisionAliases { get; init; }
+    public required int EnvCellTopologyKeys { get; init; }
     public required int SideStagedKeys { get; init; }
     public int SideStagedDuplicateKeys { get; init; }
     public required int PhysicalBlobs { get; init; }
@@ -40,6 +53,11 @@ public sealed record BakeReport
     public required long OutputBytes { get; init; }
     public required long PeakWorkingSetBytes { get; init; }
     public required long PeakPrivateBytes { get; init; }
+    public required IReadOnlyDictionary<PakAssetType, int> TypeCounts
+    {
+        get;
+        init;
+    }
 
     public double EnvCellDedupRatio =>
         UniqueEnvCellGeometries == 0 ? 0 : (double)EnvCellKeys / UniqueEnvCellGeometries;
@@ -80,7 +98,8 @@ public static class BakeRunner
             (temporaryPath, result) => BakeArtifactValidator.Validate(
                 temporaryPath,
                 result.Header,
-                result.TotalKeys),
+                result.TotalKeys,
+                result.TypeCounts),
             options.CancellationToken);
         totalStopwatch.Stop();
 
@@ -371,9 +390,402 @@ public static class BakeRunner
                 sideStagedWritten++;
             }
 
+            // ---- immutable flat collision payloads ------------------------
+
+            uint[] collisionGfxIds = gfxObjIds
+                .Concat(
+                    sideStagedByKey.Keys.Select(
+                        key => PakKey.Decompose(key).FileId))
+                .Distinct()
+                .Order()
+                .ToArray();
+            var collisionWork =
+                new List<(ulong Key, PakAssetType Type, uint FileId)>(
+                    collisionGfxIds.Length + setupIds.Count);
+            collisionWork.AddRange(
+                collisionGfxIds.Select(
+                    id => (
+                        PakKey.Compose(PakAssetType.GfxObjCollision, id),
+                        PakAssetType.GfxObjCollision,
+                        id)));
+            collisionWork.AddRange(
+                setupIds.Select(
+                    id => (
+                        PakKey.Compose(PakAssetType.SetupCollision, id),
+                        PakAssetType.SetupCollision,
+                        id)));
+            collisionWork.Sort((left, right) => left.Key.CompareTo(right.Key));
+
+            var gfxCollisionAliases = new ExactPayloadAliasCatalog();
+            var setupCollisionAliases = new ExactPayloadAliasCatalog();
+            var cellStructureAliases = new ExactPayloadAliasCatalog();
+            int gfxCollisionWritten = 0;
+            int uniqueGfxCollisions = 0;
+            int gfxCollisionAliasCount = 0;
+            int setupCollisionWritten = 0;
+            int uniqueSetupCollisions = 0;
+            int setupCollisionAliasCount = 0;
+            int cellStructureWritten = 0;
+            int uniqueCellStructures = 0;
+            int cellStructureAliasCount = 0;
+            int envCellTopologyWritten = 0;
+            long collisionCompleted = 0;
+            int totalCollisionJobs =
+                collisionWork.Count
+                + envCatalog.UniqueGeometryCount
+                + envCatalog.CellCount;
+            var collisionStopwatch = Stopwatch.StartNew();
+            lastProgressReport.Restart();
+
+            Console.WriteLine();
+            Console.WriteLine(
+                $"collision catalog: {collisionGfxIds.Length:N0} GfxObj, " +
+                $"{setupIds.Count:N0} Setup, " +
+                $"{envCatalog.UniqueGeometryCount:N0} CellStruct source groups, " +
+                $"{envCatalog.CellCount:N0} EnvCell topology records");
+
+            for (int batchStart = 0;
+                 batchStart < collisionWork.Count;
+                 batchStart += BatchSize)
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+                var batch = collisionWork
+                    .Skip(batchStart)
+                    .Take(BatchSize)
+                    .ToArray();
+                var batchResults =
+                    new ConcurrentBag<CollisionPayloadResult>();
+
+                Parallel.ForEach(
+                    batch,
+                    new ParallelOptions
+                    {
+                        MaxDegreeOfParallelism = options.Threads,
+                        CancellationToken = cancellationToken,
+                    },
+                    item =>
+                    {
+                        var (key, type, fileId) = item;
+                        try
+                        {
+                            byte[] payload;
+                            if (type == PakAssetType.GfxObjCollision)
+                            {
+                                if (!datReaderWriter.Portal.TryGet<GfxObj>(
+                                        fileId,
+                                        out GfxObj? gfxObj)
+                                    || gfxObj is null)
+                                {
+                                    failures.Add((
+                                        type,
+                                        fileId,
+                                        "GfxObj DAT record was not found"));
+                                    return;
+                                }
+
+                                FlatGfxObjCollisionAsset asset =
+                                    FlatCollisionAssetBuilder.FlattenGfxObj(
+                                        gfxObj);
+                                payload = FlatCollisionAssetSerializer.Serialize(
+                                    asset,
+                                    cancellationToken);
+                            }
+                            else
+                            {
+                                if (!datReaderWriter.Portal.TryGet<Setup>(
+                                        fileId,
+                                        out Setup? setup)
+                                    || setup is null)
+                                {
+                                    failures.Add((
+                                        type,
+                                        fileId,
+                                        "Setup DAT record was not found"));
+                                    return;
+                                }
+
+                                FlatSetupCollision asset =
+                                    FlatCollisionAssetBuilder.FlattenSetup(
+                                        setup);
+                                payload = FlatCollisionAssetSerializer.Serialize(
+                                    asset,
+                                    cancellationToken);
+                            }
+
+                            batchResults.Add(
+                                new CollisionPayloadResult(
+                                    key,
+                                    type,
+                                    fileId,
+                                    payload));
+                        }
+                        catch (OperationCanceledException)
+                        {
+                            throw;
+                        }
+                        catch (Exception exception)
+                        {
+                            failures.Add((type, fileId, exception.Message));
+                        }
+                        finally
+                        {
+                            Interlocked.Increment(ref collisionCompleted);
+                        }
+                    });
+
+                foreach (CollisionPayloadResult result in
+                         batchResults.OrderBy(result => result.Key))
+                {
+                    ExactPayloadAliasCatalog aliases =
+                        result.Type == PakAssetType.GfxObjCollision
+                            ? gfxCollisionAliases
+                            : setupCollisionAliases;
+                    bool alias = WriteExactPayload(
+                        writer,
+                        result.Key,
+                        result.Payload,
+                        aliases);
+                    writtenKeys.Add(result.Key);
+
+                    if (result.Type == PakAssetType.GfxObjCollision)
+                    {
+                        gfxCollisionWritten++;
+                        if (alias)
+                            gfxCollisionAliasCount++;
+                        else
+                            uniqueGfxCollisions++;
+                    }
+                    else
+                    {
+                        setupCollisionWritten++;
+                        if (alias)
+                            setupCollisionAliasCount++;
+                        else
+                            uniqueSetupCollisions++;
+                    }
+                }
+
+                ReportProgressIfDue(
+                    collisionCompleted,
+                    totalCollisionJobs,
+                    failures.Count,
+                    collisionStopwatch.Elapsed,
+                    lastProgressReport,
+                    final: false);
+            }
+
+            for (int groupBatchStart = 0;
+                 groupBatchStart < envCatalog.Groups.Count;
+                 groupBatchStart += BatchSize)
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+                EnvCellGeometryGroup[] groupBatch = envCatalog.Groups
+                    .Skip(groupBatchStart)
+                    .Take(BatchSize)
+                    .ToArray();
+                var structureResults =
+                    new ConcurrentBag<CellStructurePayloadResult>();
+
+                Parallel.ForEach(
+                    groupBatch,
+                    new ParallelOptions
+                    {
+                        MaxDegreeOfParallelism = options.Threads,
+                        CancellationToken = cancellationToken,
+                    },
+                    group =>
+                    {
+                        try
+                        {
+                            uint environmentDid =
+                                0x0D00_0000u | group.EnvironmentId;
+                            if (!datReaderWriter.Portal.TryGet<DatEnvironment>(
+                                    environmentDid,
+                                    out DatEnvironment? environment)
+                                || environment is null
+                                || !environment.Cells.TryGetValue(
+                                    group.CellStructure,
+                                    out CellStruct? cellStruct)
+                                || cellStruct is null)
+                            {
+                                failures.Add((
+                                    PakAssetType.CellStructureCollision,
+                                    group.FileIds[0],
+                                    $"environment 0x{environmentDid:X8} cell " +
+                                    $"structure {group.CellStructure} was not found"));
+                                Interlocked.Add(
+                                    ref collisionCompleted,
+                                    group.FileIds.Length);
+                                return;
+                            }
+
+                            FlatCellStructureCollisionAsset structure =
+                                FlatCollisionAssetBuilder.FlattenCellStructure(
+                                    cellStruct);
+                            byte[] payload =
+                                FlatCollisionAssetSerializer.Serialize(
+                                    structure,
+                                    cancellationToken);
+                            structureResults.Add(
+                                new CellStructurePayloadResult(
+                                    group,
+                                    structure,
+                                    payload));
+                        }
+                        catch (OperationCanceledException)
+                        {
+                            throw;
+                        }
+                        catch (Exception exception)
+                        {
+                            failures.Add((
+                                PakAssetType.CellStructureCollision,
+                                group.FileIds[0],
+                                exception.Message));
+                            Interlocked.Add(
+                                ref collisionCompleted,
+                                group.FileIds.Length);
+                        }
+                        finally
+                        {
+                            Interlocked.Increment(ref collisionCompleted);
+                        }
+                    });
+
+                foreach (CellStructurePayloadResult result in
+                         structureResults.OrderBy(
+                             result => result.Group.FileIds[0]))
+                {
+                    (int physical, int aliases) = WriteExactPayloadGroup(
+                        writer,
+                        PakAssetType.CellStructureCollision,
+                        result.Group.FileIds,
+                        result.Payload,
+                        cellStructureAliases,
+                        writtenKeys);
+                    cellStructureWritten += result.Group.FileIds.Length;
+                    uniqueCellStructures += physical;
+                    cellStructureAliasCount += aliases;
+
+                    for (int topologyBatchStart = 0;
+                         topologyBatchStart < result.Group.FileIds.Length;
+                         topologyBatchStart += BatchSize)
+                    {
+                        cancellationToken.ThrowIfCancellationRequested();
+                        uint[] topologyBatch = result.Group.FileIds
+                            .Skip(topologyBatchStart)
+                            .Take(BatchSize)
+                            .ToArray();
+                        var topologyResults =
+                            new ConcurrentBag<CollisionPayloadResult>();
+
+                        Parallel.ForEach(
+                            topologyBatch,
+                            new ParallelOptions
+                            {
+                                MaxDegreeOfParallelism = options.Threads,
+                                CancellationToken = cancellationToken,
+                            },
+                            fileId =>
+                            {
+                                try
+                                {
+                                    if (!datReaderWriter.Cell.TryGet<EnvCell>(
+                                            fileId,
+                                            out EnvCell? envCell)
+                                        || envCell is null)
+                                    {
+                                        failures.Add((
+                                            PakAssetType.EnvCellTopology,
+                                            fileId,
+                                            "EnvCell DAT record was not found"));
+                                        return;
+                                    }
+
+                                    FlatEnvCellTopology topology =
+                                        FlatCollisionAssetBuilder
+                                            .FlattenEnvCellTopology(
+                                                fileId,
+                                                envCell,
+                                                result.Structure
+                                                    .PortalPolygons);
+                                    byte[] payload =
+                                        FlatCollisionAssetSerializer.Serialize(
+                                            topology,
+                                            cancellationToken);
+                                    topologyResults.Add(
+                                        new CollisionPayloadResult(
+                                            PakKey.Compose(
+                                                PakAssetType.EnvCellTopology,
+                                                fileId),
+                                            PakAssetType.EnvCellTopology,
+                                            fileId,
+                                            payload));
+                                }
+                                catch (OperationCanceledException)
+                                {
+                                    throw;
+                                }
+                                catch (Exception exception)
+                                {
+                                    failures.Add((
+                                        PakAssetType.EnvCellTopology,
+                                        fileId,
+                                        exception.Message));
+                                }
+                                finally
+                                {
+                                    Interlocked.Increment(
+                                        ref collisionCompleted);
+                                }
+                            });
+
+                        foreach (CollisionPayloadResult topology in
+                                 topologyResults.OrderBy(
+                                     result => result.Key))
+                        {
+                            writer.AddBlob(
+                                topology.Key,
+                                topology.Payload);
+                            writtenKeys.Add(topology.Key);
+                            envCellTopologyWritten++;
+                        }
+
+                        ReportProgressIfDue(
+                            collisionCompleted,
+                            totalCollisionJobs,
+                            failures.Count,
+                            collisionStopwatch.Elapsed,
+                            lastProgressReport,
+                            final: false);
+                    }
+                }
+            }
+
+            collisionStopwatch.Stop();
+            ReportProgressIfDue(
+                collisionCompleted,
+                totalCollisionJobs,
+                failures.Count,
+                collisionStopwatch.Elapsed,
+                lastProgressReport,
+                final: true);
+
             writer.Finish();
             stopwatch.Stop();
 
+            var typeCounts = new Dictionary<PakAssetType, int>
+            {
+                [PakAssetType.GfxObjMesh] =
+                    gfxObjWritten + sideStagedWritten,
+                [PakAssetType.SetupMesh] = setupWritten,
+                [PakAssetType.EnvCellMesh] = envCellKeysWritten,
+                [PakAssetType.GfxObjCollision] = gfxCollisionWritten,
+                [PakAssetType.SetupCollision] = setupCollisionWritten,
+                [PakAssetType.CellStructureCollision] =
+                    cellStructureWritten,
+                [PakAssetType.EnvCellTopology] = envCellTopologyWritten,
+            };
             var report = new BakeReport
             {
                 Header = header,
@@ -382,9 +794,27 @@ public static class BakeRunner
                 EnvCellKeys = envCellKeysWritten,
                 UniqueEnvCellGeometries = envCellGeometriesWritten,
                 EnvCellAliases = envCellKeysWritten - envCellGeometriesWritten,
+                GfxObjCollisionKeys = gfxCollisionWritten,
+                UniqueGfxObjCollisions = uniqueGfxCollisions,
+                GfxObjCollisionAliases = gfxCollisionAliasCount,
+                SetupCollisionKeys = setupCollisionWritten,
+                UniqueSetupCollisions = uniqueSetupCollisions,
+                SetupCollisionAliases = setupCollisionAliasCount,
+                CellStructureCollisionKeys = cellStructureWritten,
+                UniqueCellStructureCollisions = uniqueCellStructures,
+                CellStructureCollisionAliases =
+                    cellStructureAliasCount,
+                EnvCellTopologyKeys = envCellTopologyWritten,
                 SideStagedKeys = sideStagedWritten,
                 PhysicalBlobs =
-                    gfxObjWritten + setupWritten + envCellGeometriesWritten + sideStagedWritten,
+                    gfxObjWritten
+                    + setupWritten
+                    + envCellGeometriesWritten
+                    + sideStagedWritten
+                    + uniqueGfxCollisions
+                    + uniqueSetupCollisions
+                    + uniqueCellStructures
+                    + envCellTopologyWritten,
                 TotalKeys = writtenKeys.Count,
                 Failures = failures.Count,
                 ExtractionAndWriteElapsed = stopwatch.Elapsed,
@@ -392,6 +822,7 @@ public static class BakeRunner
                 OutputBytes = new FileInfo(options.OutPath).Length,
                 PeakWorkingSetBytes = Process.GetCurrentProcess().PeakWorkingSet64,
                 PeakPrivateBytes = Process.GetCurrentProcess().PeakPagedMemorySize64,
+                TypeCounts = typeCounts,
             };
 
             report = report with { SideStagedDuplicateKeys = sideStagedDuped };
@@ -400,6 +831,63 @@ public static class BakeRunner
         }
     }
 
+    private static bool WriteExactPayload(
+        PakWriter writer,
+        ulong key,
+        byte[] payload,
+        ExactPayloadAliasCatalog aliases)
+    {
+        if (aliases.TryFind(payload, out ulong primaryKey))
+        {
+            writer.AddAlias(key, primaryKey);
+            return true;
+        }
+
+        writer.AddBlob(key, payload);
+        aliases.Add(key, payload);
+        return false;
+    }
+
+    private static (int Physical, int Aliases) WriteExactPayloadGroup(
+        PakWriter writer,
+        PakAssetType type,
+        IReadOnlyList<uint> fileIds,
+        byte[] payload,
+        ExactPayloadAliasCatalog aliases,
+        HashSet<ulong> writtenKeys)
+    {
+        if (fileIds.Count == 0)
+            throw new InvalidDataException("collision alias group is empty");
+
+        int firstUnwrittenIndex = 0;
+        ulong primaryKey;
+        int physical;
+        if (aliases.TryFind(payload, out primaryKey))
+        {
+            physical = 0;
+        }
+        else
+        {
+            primaryKey = PakKey.Compose(type, fileIds[0]);
+            writer.AddBlob(primaryKey, payload);
+            aliases.Add(primaryKey, payload);
+            writtenKeys.Add(primaryKey);
+            firstUnwrittenIndex = 1;
+            physical = 1;
+        }
+
+        int aliasCount = 0;
+        for (int i = firstUnwrittenIndex; i < fileIds.Count; i++)
+        {
+            ulong aliasKey = PakKey.Compose(type, fileIds[i]);
+            writer.AddAlias(aliasKey, primaryKey);
+            writtenKeys.Add(aliasKey);
+            aliasCount++;
+        }
+
+        return (physical, aliasCount);
+    }
+
     private static int DrainSideStaged(
         ConcurrentQueue<ObjectMeshData> sideStaged,
         Dictionary<ulong, ObjectMeshData> sideStagedByKey,
@@ -450,6 +938,20 @@ public static class BakeRunner
         Console.WriteLine($"  EnvCell unique:   {report.UniqueEnvCellGeometries:N0}");
         Console.WriteLine($"  EnvCell aliases:  {report.EnvCellAliases:N0}");
         Console.WriteLine($"  EnvCell dedup:    {report.EnvCellDedupRatio:F1}x");
+        Console.WriteLine(
+            $"  Gfx collisions:   {report.GfxObjCollisionKeys:N0} keys, " +
+            $"{report.UniqueGfxObjCollisions:N0} blobs, " +
+            $"{report.GfxObjCollisionAliases:N0} aliases");
+        Console.WriteLine(
+            $"  Setup collisions: {report.SetupCollisionKeys:N0} keys, " +
+            $"{report.UniqueSetupCollisions:N0} blobs, " +
+            $"{report.SetupCollisionAliases:N0} aliases");
+        Console.WriteLine(
+            $"  Cell structures:  {report.CellStructureCollisionKeys:N0} keys, " +
+            $"{report.UniqueCellStructureCollisions:N0} blobs, " +
+            $"{report.CellStructureCollisionAliases:N0} aliases");
+        Console.WriteLine(
+            $"  Cell topologies:   {report.EnvCellTopologyKeys:N0}");
         Console.WriteLine(
             $"  side-staged keys: {report.SideStagedKeys:N0} " +
             $"({report.SideStagedDuplicateKeys:N0} duplicate keys)");
@@ -526,4 +1028,15 @@ public static class BakeRunner
 
         return envCellIds;
     }
+
+    private sealed record CollisionPayloadResult(
+        ulong Key,
+        PakAssetType Type,
+        uint FileId,
+        byte[] Payload);
+
+    private sealed record CellStructurePayloadResult(
+        EnvCellGeometryGroup Group,
+        FlatCellStructureCollisionAsset Structure,
+        byte[] Payload);
 }
diff --git a/src/AcDream.Bake/ExactPayloadAliasCatalog.cs b/src/AcDream.Bake/ExactPayloadAliasCatalog.cs
new file mode 100644
index 00000000..84cc3bb1
--- /dev/null
+++ b/src/AcDream.Bake/ExactPayloadAliasCatalog.cs
@@ -0,0 +1,50 @@
+using System.Security.Cryptography;
+
+namespace AcDream.Bake;
+
+/// <summary>
+/// Offline-only exact-byte deduplication catalog. SHA-256 narrows candidates;
+/// a complete byte comparison is still mandatory before any alias is emitted.
+/// </summary>
+internal sealed class ExactPayloadAliasCatalog
+{
+    private readonly Dictionary<string, List<Entry>> _entriesByDigest =
+        new(StringComparer.Ordinal);
+
+    public bool TryFind(ReadOnlySpan<byte> payload, out ulong primaryKey)
+    {
+        string digest = Digest(payload);
+        if (_entriesByDigest.TryGetValue(digest, out List<Entry>? candidates))
+        {
+            foreach (Entry candidate in candidates)
+            {
+                if (payload.SequenceEqual(candidate.Payload))
+                {
+                    primaryKey = candidate.PrimaryKey;
+                    return true;
+                }
+            }
+        }
+
+        primaryKey = 0;
+        return false;
+    }
+
+    public void Add(ulong primaryKey, byte[] payload)
+    {
+        ArgumentNullException.ThrowIfNull(payload);
+        string digest = Digest(payload);
+        if (!_entriesByDigest.TryGetValue(digest, out List<Entry>? entries))
+        {
+            entries = [];
+            _entriesByDigest.Add(digest, entries);
+        }
+
+        entries.Add(new Entry(primaryKey, payload));
+    }
+
+    private static string Digest(ReadOnlySpan<byte> payload) =>
+        Convert.ToHexString(SHA256.HashData(payload));
+
+    private sealed record Entry(ulong PrimaryKey, byte[] Payload);
+}
diff --git a/src/AcDream.Content/FlatCollisionAssetSerializer.cs b/src/AcDream.Content/FlatCollisionAssetSerializer.cs
new file mode 100644
index 00000000..ba6e34f4
--- /dev/null
+++ b/src/AcDream.Content/FlatCollisionAssetSerializer.cs
@@ -0,0 +1,715 @@
+using System.Buffers;
+using System.Buffers.Binary;
+using System.Collections.Immutable;
+using System.Numerics;
+using AcDream.Core.Physics;
+using DatReaderWriter.Enums;
+
+namespace AcDream.Content;
+
+/// <summary>
+/// Strict little-endian package codec for immutable flat collision assets.
+/// Every float is persisted through its exact IEEE-754 bit pattern. Readers
+/// reject invalid counts, invalid enum/range/tree contracts, wrong payload
+/// kinds, non-zero reserved bytes, truncation, and trailing bytes.
+/// </summary>
+public static class FlatCollisionAssetSerializer
+{
+    private const uint Magic = 0x4C_43_43_41u; // "ACCL" little-endian
+    private const byte SchemaVersion = 1;
+    private const int MaximumRows = 16_777_216;
+
+    public static byte[] Serialize(
+        FlatGfxObjCollisionAsset asset,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(asset);
+        var writer = new CollisionWriter();
+        writer.WriteHeader(CollisionPayloadKind.GfxObj);
+        WritePhysicsBsp(writer, asset.PhysicsBsp, cancellationToken);
+        writer.WriteOptionalSphere(asset.BoundingSphere);
+        writer.WriteBoolean(asset.VisualBounds.HasValue);
+        if (asset.VisualBounds is FlatGfxObjVisualBounds visual)
+        {
+            writer.WriteVector3(visual.Min);
+            writer.WriteVector3(visual.Max);
+            writer.WriteVector3(visual.Center);
+            writer.WriteSingle(visual.Radius);
+            writer.WriteVector3(visual.HalfExtents);
+        }
+        cancellationToken.ThrowIfCancellationRequested();
+        return writer.ToArray();
+    }
+
+    public static byte[] Serialize(
+        FlatSetupCollision asset,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(asset);
+        var writer = new CollisionWriter();
+        writer.WriteHeader(CollisionPayloadKind.Setup);
+        writer.WriteCount(asset.Cylinders.Length, "Setup cylinder");
+        writer.WriteCount(asset.Spheres.Length, "Setup sphere");
+        writer.WriteSingle(asset.Height);
+        writer.WriteSingle(asset.Radius);
+        writer.WriteSingle(asset.StepUpHeight);
+        writer.WriteSingle(asset.StepDownHeight);
+
+        for (int i = 0; i < asset.Cylinders.Length; i++)
+        {
+            CheckCancellation(cancellationToken, i);
+            FlatCollisionCylinder cylinder = asset.Cylinders[i];
+            writer.WriteVector3(cylinder.Origin);
+            writer.WriteSingle(cylinder.Radius);
+            writer.WriteSingle(cylinder.Height);
+        }
+        for (int i = 0; i < asset.Spheres.Length; i++)
+        {
+            CheckCancellation(cancellationToken, i);
+            writer.WriteSphere(asset.Spheres[i]);
+        }
+
+        cancellationToken.ThrowIfCancellationRequested();
+        return writer.ToArray();
+    }
+
+    public static byte[] Serialize(
+        FlatCellStructureCollisionAsset asset,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(asset);
+        var writer = new CollisionWriter();
+        writer.WriteHeader(CollisionPayloadKind.CellStructure);
+        WritePhysicsBsp(writer, asset.PhysicsBsp, cancellationToken);
+        WriteContainmentBsp(writer, asset.ContainmentBsp, cancellationToken);
+        WritePolygonTable(writer, asset.PortalPolygons, cancellationToken);
+        cancellationToken.ThrowIfCancellationRequested();
+        return writer.ToArray();
+    }
+
+    public static byte[] Serialize(
+        FlatEnvCellTopology asset,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(asset);
+        var writer = new CollisionWriter();
+        writer.WriteHeader(CollisionPayloadKind.EnvCellTopology);
+        writer.WriteCount(asset.Portals.Length, "EnvCell portal");
+        writer.WriteCount(asset.VisibleCellIds.Length, "visible-cell");
+        writer.WriteBoolean(asset.SeenOutside);
+
+        for (int i = 0; i < asset.Portals.Length; i++)
+        {
+            CheckCancellation(cancellationToken, i);
+            FlatEnvCellPortal portal = asset.Portals[i];
+            writer.WriteUInt16(portal.OtherCellId);
+            writer.WriteUInt16(portal.PolygonId);
+            writer.WriteUInt16(portal.Flags);
+            writer.WriteInt32(portal.PolygonIndex);
+        }
+        for (int i = 0; i < asset.VisibleCellIds.Length; i++)
+        {
+            CheckCancellation(cancellationToken, i);
+            writer.WriteUInt32(asset.VisibleCellIds[i]);
+        }
+
+        cancellationToken.ThrowIfCancellationRequested();
+        return writer.ToArray();
+    }
+
+    public static FlatGfxObjCollisionAsset DeserializeGfxObj(
+        ReadOnlySpan<byte> bytes,
+        CancellationToken cancellationToken = default)
+    {
+        var reader = new CollisionReader(bytes, cancellationToken);
+        reader.ReadHeader(CollisionPayloadKind.GfxObj);
+        FlatPhysicsBsp physicsBsp = ReadPhysicsBsp(ref reader);
+        FlatCollisionSphere? boundingSphere = reader.ReadOptionalSphere();
+        FlatGfxObjVisualBounds? visualBounds = null;
+        if (reader.ReadBoolean())
+        {
+            visualBounds = new FlatGfxObjVisualBounds(
+                reader.ReadVector3(),
+                reader.ReadVector3(),
+                reader.ReadVector3(),
+                reader.ReadSingle(),
+                reader.ReadVector3());
+        }
+        reader.RequireEnd();
+        return new FlatGfxObjCollisionAsset(
+            physicsBsp,
+            boundingSphere,
+            visualBounds);
+    }
+
+    public static FlatSetupCollision DeserializeSetup(
+        ReadOnlySpan<byte> bytes,
+        CancellationToken cancellationToken = default)
+    {
+        var reader = new CollisionReader(bytes, cancellationToken);
+        reader.ReadHeader(CollisionPayloadKind.Setup);
+        int cylinderCount = reader.ReadCount(
+            "Setup cylinder",
+            bytesPerItem: 20);
+        int sphereCount = reader.ReadCount(
+            "Setup sphere",
+            bytesPerItem: 16);
+        reader.RequireRemaining(
+            checked(16L + (20L * cylinderCount) + (16L * sphereCount)),
+            "Setup collision rows");
+        float height = reader.ReadSingle();
+        float radius = reader.ReadSingle();
+        float stepUpHeight = reader.ReadSingle();
+        float stepDownHeight = reader.ReadSingle();
+
+        var cylinders =
+            ImmutableArray.CreateBuilder<FlatCollisionCylinder>(cylinderCount);
+        for (int i = 0; i < cylinderCount; i++)
+        {
+            reader.CheckCancellation(i);
+            cylinders.Add(new FlatCollisionCylinder(
+                reader.ReadVector3(),
+                reader.ReadSingle(),
+                reader.ReadSingle()));
+        }
+
+        var spheres =
+            ImmutableArray.CreateBuilder<FlatCollisionSphere>(sphereCount);
+        for (int i = 0; i < sphereCount; i++)
+        {
+            reader.CheckCancellation(i);
+            spheres.Add(reader.ReadSphere());
+        }
+
+        reader.RequireEnd();
+        return new FlatSetupCollision(
+            cylinders.MoveToImmutable(),
+            spheres.MoveToImmutable(),
+            height,
+            radius,
+            stepUpHeight,
+            stepDownHeight);
+    }
+
+    public static FlatCellStructureCollisionAsset DeserializeCellStructure(
+        ReadOnlySpan<byte> bytes,
+        CancellationToken cancellationToken = default)
+    {
+        var reader = new CollisionReader(bytes, cancellationToken);
+        reader.ReadHeader(CollisionPayloadKind.CellStructure);
+        FlatPhysicsBsp physicsBsp = ReadPhysicsBsp(ref reader);
+        FlatCellContainmentBsp containmentBsp = ReadContainmentBsp(ref reader);
+        FlatPolygonTable portalPolygons = ReadPolygonTable(ref reader);
+        reader.RequireEnd();
+        return new FlatCellStructureCollisionAsset(
+            physicsBsp,
+            containmentBsp,
+            portalPolygons);
+    }
+
+    public static FlatEnvCellTopology DeserializeEnvCellTopology(
+        ReadOnlySpan<byte> bytes,
+        CancellationToken cancellationToken = default)
+    {
+        var reader = new CollisionReader(bytes, cancellationToken);
+        reader.ReadHeader(CollisionPayloadKind.EnvCellTopology);
+        int portalCount = reader.ReadCount(
+            "EnvCell portal",
+            bytesPerItem: 10);
+        int visibleCount = reader.ReadCount(
+            "visible-cell",
+            bytesPerItem: 4);
+        reader.RequireRemaining(
+            checked(1L + (10L * portalCount) + (4L * visibleCount)),
+            "EnvCell topology rows");
+        bool seenOutside = reader.ReadBoolean();
+
+        var portals =
+            ImmutableArray.CreateBuilder<FlatEnvCellPortal>(portalCount);
+        for (int i = 0; i < portalCount; i++)
+        {
+            reader.CheckCancellation(i);
+            portals.Add(new FlatEnvCellPortal(
+                reader.ReadUInt16(),
+                reader.ReadUInt16(),
+                reader.ReadUInt16(),
+                reader.ReadInt32()));
+        }
+
+        var visible =
+            ImmutableArray.CreateBuilder<uint>(visibleCount);
+        for (int i = 0; i < visibleCount; i++)
+        {
+            reader.CheckCancellation(i);
+            visible.Add(reader.ReadUInt32());
+        }
+
+        reader.RequireEnd();
+        return new FlatEnvCellTopology(
+            portals.MoveToImmutable(),
+            visible.MoveToImmutable(),
+            seenOutside);
+    }
+
+    private static void WritePhysicsBsp(
+        CollisionWriter writer,
+        FlatPhysicsBsp bsp,
+        CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(bsp);
+        writer.WriteInt32(bsp.RootIndex);
+        writer.WriteCount(bsp.Nodes.Length, "physics BSP node");
+        writer.WriteCount(
+            bsp.PolygonIndexStream.Length,
+            "physics BSP polygon-index");
+
+        for (int i = 0; i < bsp.Nodes.Length; i++)
+        {
+            CheckCancellation(cancellationToken, i);
+            FlatPhysicsBspNode node = bsp.Nodes[i];
+            writer.WriteUInt32((uint)node.Type);
+            writer.WritePlane(node.SplittingPlane);
+            writer.WriteInt32(node.PositiveChildIndex);
+            writer.WriteInt32(node.NegativeChildIndex);
+            writer.WriteInt32(node.LeafIndex);
+            writer.WriteInt32(node.Solid);
+            writer.WriteSphere(node.BoundingSphere);
+            writer.WriteRange(node.PolygonIndexRange);
+        }
+
+        for (int i = 0; i < bsp.PolygonIndexStream.Length; i++)
+        {
+            CheckCancellation(cancellationToken, i);
+            writer.WriteInt32(bsp.PolygonIndexStream[i]);
+        }
+        WritePolygonTable(writer, bsp.PolygonTable, cancellationToken);
+    }
+
+    private static FlatPhysicsBsp ReadPhysicsBsp(
+        ref CollisionReader reader)
+    {
+        int rootIndex = reader.ReadInt32();
+        int nodeCount = reader.ReadCount(
+            "physics BSP node",
+            bytesPerItem: 60);
+        int polygonIndexCount = reader.ReadCount(
+            "physics BSP polygon-index",
+            bytesPerItem: 4);
+        reader.RequireRemaining(
+            checked((60L * nodeCount) + (4L * polygonIndexCount) + 8L),
+            "physics BSP rows");
+
+        var nodes =
+            ImmutableArray.CreateBuilder<FlatPhysicsBspNode>(nodeCount);
+        for (int i = 0; i < nodeCount; i++)
+        {
+            reader.CheckCancellation(i);
+            nodes.Add(new FlatPhysicsBspNode(
+                (BSPNodeType)reader.ReadUInt32(),
+                reader.ReadPlane(),
+                reader.ReadInt32(),
+                reader.ReadInt32(),
+                reader.ReadInt32(),
+                reader.ReadInt32(),
+                reader.ReadSphere(),
+                reader.ReadRange()));
+        }
+
+        var polygonIndices =
+            ImmutableArray.CreateBuilder<int>(polygonIndexCount);
+        for (int i = 0; i < polygonIndexCount; i++)
+        {
+            reader.CheckCancellation(i);
+            polygonIndices.Add(reader.ReadInt32());
+        }
+
+        FlatPolygonTable polygons = ReadPolygonTable(ref reader);
+        return new FlatPhysicsBsp(
+            rootIndex,
+            nodes.MoveToImmutable(),
+            polygonIndices.MoveToImmutable(),
+            polygons);
+    }
+
+    private static void WriteContainmentBsp(
+        CollisionWriter writer,
+        FlatCellContainmentBsp bsp,
+        CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(bsp);
+        writer.WriteInt32(bsp.RootIndex);
+        writer.WriteCount(bsp.Nodes.Length, "cell-containment BSP node");
+        for (int i = 0; i < bsp.Nodes.Length; i++)
+        {
+            CheckCancellation(cancellationToken, i);
+            FlatCellBspNode node = bsp.Nodes[i];
+            writer.WriteUInt32((uint)node.Type);
+            writer.WritePlane(node.SplittingPlane);
+            writer.WriteInt32(node.PositiveChildIndex);
+            writer.WriteInt32(node.NegativeChildIndex);
+            writer.WriteInt32(node.LeafIndex);
+        }
+    }
+
+    private static FlatCellContainmentBsp ReadContainmentBsp(
+        ref CollisionReader reader)
+    {
+        int rootIndex = reader.ReadInt32();
+        int nodeCount = reader.ReadCount(
+            "cell-containment BSP node",
+            bytesPerItem: 32);
+        var nodes =
+            ImmutableArray.CreateBuilder<FlatCellBspNode>(nodeCount);
+        for (int i = 0; i < nodeCount; i++)
+        {
+            reader.CheckCancellation(i);
+            nodes.Add(new FlatCellBspNode(
+                (BSPNodeType)reader.ReadUInt32(),
+                reader.ReadPlane(),
+                reader.ReadInt32(),
+                reader.ReadInt32(),
+                reader.ReadInt32()));
+        }
+        return new FlatCellContainmentBsp(
+            rootIndex,
+            nodes.MoveToImmutable());
+    }
+
+    private static void WritePolygonTable(
+        CollisionWriter writer,
+        FlatPolygonTable table,
+        CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(table);
+        writer.WriteCount(table.Polygons.Length, "polygon");
+        writer.WriteCount(table.Vertices.Length, "polygon vertex");
+        for (int i = 0; i < table.Polygons.Length; i++)
+        {
+            CheckCancellation(cancellationToken, i);
+            FlatCollisionPolygon polygon = table.Polygons[i];
+            writer.WriteUInt16(polygon.Id);
+            writer.WriteUInt32((uint)polygon.SidesType);
+            writer.WriteInt32(polygon.NumPoints);
+            writer.WriteRange(polygon.VertexRange);
+            writer.WritePlane(polygon.Plane);
+        }
+        for (int i = 0; i < table.Vertices.Length; i++)
+        {
+            CheckCancellation(cancellationToken, i);
+            writer.WriteVector3(table.Vertices[i]);
+        }
+    }
+
+    private static FlatPolygonTable ReadPolygonTable(
+        ref CollisionReader reader)
+    {
+        int polygonCount = reader.ReadCount(
+            "polygon",
+            bytesPerItem: 34);
+        int vertexCount = reader.ReadCount(
+            "polygon vertex",
+            bytesPerItem: 12);
+        reader.RequireRemaining(
+            checked((34L * polygonCount) + (12L * vertexCount)),
+            "polygon-table rows");
+        var polygons =
+            ImmutableArray.CreateBuilder<FlatCollisionPolygon>(polygonCount);
+        for (int i = 0; i < polygonCount; i++)
+        {
+            reader.CheckCancellation(i);
+            polygons.Add(new FlatCollisionPolygon(
+                reader.ReadUInt16(),
+                reader.ReadPlaneAfterMetadata(out CullMode sides, out int count,
+                    out FlatIndexRange range),
+                sides,
+                count,
+                range));
+        }
+
+        var vertices = ImmutableArray.CreateBuilder<Vector3>(vertexCount);
+        for (int i = 0; i < vertexCount; i++)
+        {
+            reader.CheckCancellation(i);
+            vertices.Add(reader.ReadVector3());
+        }
+        return new FlatPolygonTable(
+            polygons.MoveToImmutable(),
+            vertices.MoveToImmutable());
+    }
+
+    private static void CheckCancellation(
+        CancellationToken cancellationToken,
+        int index)
+    {
+        if ((index & 0xFF) == 0)
+            cancellationToken.ThrowIfCancellationRequested();
+    }
+
+    private enum CollisionPayloadKind : byte
+    {
+        GfxObj = 1,
+        Setup = 2,
+        CellStructure = 3,
+        EnvCellTopology = 4,
+    }
+
+    private sealed class CollisionWriter
+    {
+        private readonly ArrayBufferWriter<byte> _buffer = new(256);
+
+        public void WriteHeader(CollisionPayloadKind kind)
+        {
+            WriteUInt32(Magic);
+            WriteByte((byte)kind);
+            WriteByte(SchemaVersion);
+            WriteUInt16(0);
+        }
+
+        public void WriteCount(int value, string name)
+        {
+            if ((uint)value > MaximumRows)
+            {
+                throw new InvalidDataException(
+                    $"{name} count {value} exceeds {MaximumRows}.");
+            }
+            WriteInt32(value);
+        }
+
+        public void WriteOptionalSphere(FlatCollisionSphere? sphere)
+        {
+            WriteBoolean(sphere.HasValue);
+            if (sphere.HasValue)
+                WriteSphere(sphere.Value);
+        }
+
+        public void WriteBoolean(bool value) => WriteByte(value ? (byte)1 : (byte)0);
+
+        public void WriteSphere(FlatCollisionSphere sphere)
+        {
+            WriteVector3(sphere.Origin);
+            WriteSingle(sphere.Radius);
+        }
+
+        public void WriteRange(FlatIndexRange range)
+        {
+            WriteInt32(range.Start);
+            WriteInt32(range.Count);
+        }
+
+        public void WritePlane(Plane plane)
+        {
+            WriteVector3(plane.Normal);
+            WriteSingle(plane.D);
+        }
+
+        public void WriteVector3(Vector3 vector)
+        {
+            WriteSingle(vector.X);
+            WriteSingle(vector.Y);
+            WriteSingle(vector.Z);
+        }
+
+        public void WriteSingle(float value) =>
+            WriteInt32(BitConverter.SingleToInt32Bits(value));
+
+        public void WriteByte(byte value)
+        {
+            Span<byte> span = _buffer.GetSpan(1);
+            span[0] = value;
+            _buffer.Advance(1);
+        }
+
+        public void WriteUInt16(ushort value)
+        {
+            Span<byte> span = _buffer.GetSpan(sizeof(ushort));
+            BinaryPrimitives.WriteUInt16LittleEndian(span, value);
+            _buffer.Advance(sizeof(ushort));
+        }
+
+        public void WriteInt32(int value)
+        {
+            Span<byte> span = _buffer.GetSpan(sizeof(int));
+            BinaryPrimitives.WriteInt32LittleEndian(span, value);
+            _buffer.Advance(sizeof(int));
+        }
+
+        public void WriteUInt32(uint value)
+        {
+            Span<byte> span = _buffer.GetSpan(sizeof(uint));
+            BinaryPrimitives.WriteUInt32LittleEndian(span, value);
+            _buffer.Advance(sizeof(uint));
+        }
+
+        public byte[] ToArray() => _buffer.WrittenSpan.ToArray();
+    }
+
+    private ref struct CollisionReader
+    {
+        private readonly ReadOnlySpan<byte> _bytes;
+        private readonly CancellationToken _cancellationToken;
+        private int _offset;
+
+        public CollisionReader(
+            ReadOnlySpan<byte> bytes,
+            CancellationToken cancellationToken)
+        {
+            _bytes = bytes;
+            _cancellationToken = cancellationToken;
+            _offset = 0;
+            _cancellationToken.ThrowIfCancellationRequested();
+        }
+
+        private int Remaining => _bytes.Length - _offset;
+
+        public void ReadHeader(CollisionPayloadKind expectedKind)
+        {
+            uint magic = ReadUInt32();
+            byte kind = ReadByte();
+            byte version = ReadByte();
+            ushort reserved = ReadUInt16();
+            if (magic != Magic)
+            {
+                throw new InvalidDataException(
+                    $"collision payload magic 0x{magic:X8} does not match " +
+                    $"0x{Magic:X8}.");
+            }
+            if (kind != (byte)expectedKind)
+            {
+                throw new InvalidDataException(
+                    $"collision payload kind {kind} does not match " +
+                    $"{(byte)expectedKind}.");
+            }
+            if (version != SchemaVersion)
+            {
+                throw new InvalidDataException(
+                    $"collision payload schema {version} is unsupported.");
+            }
+            if (reserved != 0)
+            {
+                throw new InvalidDataException(
+                    "collision payload reserved header bits are non-zero.");
+            }
+        }
+
+        public int ReadCount(string name, int bytesPerItem)
+        {
+            int count = ReadInt32();
+            if (count < 0 || count > MaximumRows)
+            {
+                throw new InvalidDataException(
+                    $"{name} count {count} is outside [0,{MaximumRows}].");
+            }
+            if (bytesPerItem <= 0 || count > Remaining / bytesPerItem)
+            {
+                throw new InvalidDataException(
+                    $"{name} count {count} exceeds the remaining payload.");
+            }
+            return count;
+        }
+
+        public FlatCollisionSphere? ReadOptionalSphere() =>
+            ReadBoolean() ? ReadSphere() : null;
+
+        public bool ReadBoolean()
+        {
+            byte value = ReadByte();
+            return value switch
+            {
+                0 => false,
+                1 => true,
+                _ => throw new InvalidDataException(
+                    $"invalid collision boolean value {value}."),
+            };
+        }
+
+        public FlatCollisionSphere ReadSphere() =>
+            new(ReadVector3(), ReadSingle());
+
+        public FlatIndexRange ReadRange() =>
+            new(ReadInt32(), ReadInt32());
+
+        public Plane ReadPlane() =>
+            new(ReadVector3(), ReadSingle());
+
+        public Plane ReadPlaneAfterMetadata(
+            out CullMode sides,
+            out int numPoints,
+            out FlatIndexRange range)
+        {
+            sides = (CullMode)ReadUInt32();
+            numPoints = ReadInt32();
+            range = ReadRange();
+            return ReadPlane();
+        }
+
+        public Vector3 ReadVector3() =>
+            new(ReadSingle(), ReadSingle(), ReadSingle());
+
+        public float ReadSingle() =>
+            BitConverter.Int32BitsToSingle(ReadInt32());
+
+        public byte ReadByte()
+        {
+            Require(sizeof(byte));
+            return _bytes[_offset++];
+        }
+
+        public ushort ReadUInt16()
+        {
+            ReadOnlySpan<byte> span = Take(sizeof(ushort));
+            return BinaryPrimitives.ReadUInt16LittleEndian(span);
+        }
+
+        public int ReadInt32()
+        {
+            ReadOnlySpan<byte> span = Take(sizeof(int));
+            return BinaryPrimitives.ReadInt32LittleEndian(span);
+        }
+
+        public uint ReadUInt32()
+        {
+            ReadOnlySpan<byte> span = Take(sizeof(uint));
+            return BinaryPrimitives.ReadUInt32LittleEndian(span);
+        }
+
+        public void CheckCancellation(int index)
+        {
+            if ((index & 0xFF) == 0)
+                _cancellationToken.ThrowIfCancellationRequested();
+        }
+
+        public void RequireEnd()
+        {
+            _cancellationToken.ThrowIfCancellationRequested();
+            if (_offset != _bytes.Length)
+            {
+                throw new InvalidDataException(
+                    $"collision payload contains {_bytes.Length - _offset} " +
+                    "trailing byte(s).");
+            }
+        }
+
+        public void RequireRemaining(long required, string name)
+        {
+            if (required < 0 || required > Remaining)
+            {
+                throw new InvalidDataException(
+                    $"{name} require {required} bytes but only {Remaining} remain.");
+            }
+        }
+
+        private ReadOnlySpan<byte> Take(int length)
+        {
+            Require(length);
+            ReadOnlySpan<byte> result = _bytes.Slice(_offset, length);
+            _offset += length;
+            return result;
+        }
+
+        private void Require(int length)
+        {
+            if (length < 0 || length > Remaining)
+                throw new EndOfStreamException("collision payload is truncated.");
+        }
+    }
+}
diff --git a/src/AcDream.Content/IPreparedAssetSource.cs b/src/AcDream.Content/IPreparedAssetSource.cs
index 46662c0b..f9f58659 100644
--- a/src/AcDream.Content/IPreparedAssetSource.cs
+++ b/src/AcDream.Content/IPreparedAssetSource.cs
@@ -131,7 +131,10 @@ internal static class PreparedAssetRequestContract
 {
     public static void ValidateType(PakAssetType type)
     {
-        if (!Enum.IsDefined(type))
+        if (type is not (
+            PakAssetType.GfxObjMesh or
+            PakAssetType.SetupMesh or
+            PakAssetType.EnvCellMesh))
         {
             throw new ArgumentOutOfRangeException(
                 nameof(type),
@@ -166,7 +169,9 @@ internal static class PreparedAssetRequestContract
 /// Production prepared source backed by one immutable memory-mapped pak.
 /// There is intentionally no DAT fallback.
 /// </summary>
-public sealed class PakPreparedAssetSource : IPreparedAssetSource
+public sealed partial class PakPreparedAssetSource :
+    IPreparedAssetSource,
+    IPreparedCollisionSource
 {
     private readonly PakReader _reader;
     private readonly Action<string>? _diagnosticSink;
diff --git a/src/AcDream.Content/IPreparedCollisionSource.cs b/src/AcDream.Content/IPreparedCollisionSource.cs
new file mode 100644
index 00000000..87e1ba52
--- /dev/null
+++ b/src/AcDream.Content/IPreparedCollisionSource.cs
@@ -0,0 +1,206 @@
+using AcDream.Content.Pak;
+using AcDream.Core.Physics;
+
+namespace AcDream.Content;
+
+public readonly record struct PreparedCollisionSourceStats(
+    long Probes,
+    long Reads,
+    long Loaded,
+    long Missing,
+    long Corrupt);
+
+public readonly record struct PreparedCollisionReadResult<T>(
+    PreparedAssetReadStatus Status,
+    T? Data)
+    where T : class
+{
+    public static PreparedCollisionReadResult<T> Missing =>
+        new(PreparedAssetReadStatus.Missing, null);
+
+    public static PreparedCollisionReadResult<T> Corrupt =>
+        new(PreparedAssetReadStatus.Corrupt, null);
+
+    public static PreparedCollisionReadResult<T> Loaded(T data) =>
+        new(PreparedAssetReadStatus.Loaded, data);
+}
+
+/// <summary>
+/// Typed immutable collision payload source. It is deliberately separate from
+/// the render-only <see cref="IPreparedAssetSource"/> contract even when one
+/// concrete package owner implements both interfaces over the same mmap.
+/// </summary>
+public interface IPreparedCollisionSource : IDisposable
+{
+    PreparedAssetPresence ProbeCollision(
+        PakAssetType type,
+        uint sourceFileId);
+
+    PreparedCollisionReadResult<FlatGfxObjCollisionAsset>
+        ReadGfxObjCollision(
+            uint sourceFileId,
+            CancellationToken cancellationToken = default);
+
+    PreparedCollisionReadResult<FlatSetupCollision>
+        ReadSetupCollision(
+            uint sourceFileId,
+            CancellationToken cancellationToken = default);
+
+    PreparedCollisionReadResult<FlatCellStructureCollisionAsset>
+        ReadCellStructureCollision(
+            uint sourceFileId,
+            CancellationToken cancellationToken = default);
+
+    PreparedCollisionReadResult<FlatEnvCellTopology>
+        ReadEnvCellTopology(
+            uint sourceFileId,
+            CancellationToken cancellationToken = default);
+
+    PreparedCollisionSourceStats CollisionStats { get; }
+}
+
+internal static class PreparedCollisionTypeContract
+{
+    public static void Validate(PakAssetType type)
+    {
+        if (type is not (
+            PakAssetType.GfxObjCollision or
+            PakAssetType.SetupCollision or
+            PakAssetType.CellStructureCollision or
+            PakAssetType.EnvCellTopology))
+        {
+            throw new ArgumentOutOfRangeException(
+                nameof(type),
+                type,
+                "unknown prepared collision asset type");
+        }
+    }
+}
+
+public sealed partial class PakPreparedAssetSource
+{
+    private long _collisionProbes;
+    private long _collisionReads;
+    private long _collisionLoaded;
+    private long _collisionMissing;
+    private long _collisionCorrupt;
+
+    public PreparedCollisionSourceStats CollisionStats =>
+        new(
+            Volatile.Read(ref _collisionProbes),
+            Volatile.Read(ref _collisionReads),
+            Volatile.Read(ref _collisionLoaded),
+            Volatile.Read(ref _collisionMissing),
+            Volatile.Read(ref _collisionCorrupt));
+
+    public PreparedAssetPresence ProbeCollision(
+        PakAssetType type,
+        uint sourceFileId)
+    {
+        PreparedCollisionTypeContract.Validate(type);
+        Interlocked.Increment(ref _collisionProbes);
+        ulong key = PakKey.Compose(type, sourceFileId);
+        return _reader.ProbeEntry(key) switch
+        {
+            PakEntryState.Available => PreparedAssetPresence.Available,
+            PakEntryState.Corrupt => PreparedAssetPresence.Corrupt,
+            _ => PreparedAssetPresence.Missing,
+        };
+    }
+
+    public PreparedCollisionReadResult<FlatGfxObjCollisionAsset>
+        ReadGfxObjCollision(
+            uint sourceFileId,
+            CancellationToken cancellationToken = default) =>
+        ReadCollision(
+            PakAssetType.GfxObjCollision,
+            sourceFileId,
+            static (bytes, token) =>
+                FlatCollisionAssetSerializer.DeserializeGfxObj(bytes, token),
+            cancellationToken);
+
+    public PreparedCollisionReadResult<FlatSetupCollision>
+        ReadSetupCollision(
+            uint sourceFileId,
+            CancellationToken cancellationToken = default) =>
+        ReadCollision(
+            PakAssetType.SetupCollision,
+            sourceFileId,
+            static (bytes, token) =>
+                FlatCollisionAssetSerializer.DeserializeSetup(bytes, token),
+            cancellationToken);
+
+    public PreparedCollisionReadResult<FlatCellStructureCollisionAsset>
+        ReadCellStructureCollision(
+            uint sourceFileId,
+            CancellationToken cancellationToken = default) =>
+        ReadCollision(
+            PakAssetType.CellStructureCollision,
+            sourceFileId,
+            static (bytes, token) =>
+                FlatCollisionAssetSerializer.DeserializeCellStructure(
+                    bytes,
+                    token),
+            cancellationToken);
+
+    public PreparedCollisionReadResult<FlatEnvCellTopology>
+        ReadEnvCellTopology(
+            uint sourceFileId,
+            CancellationToken cancellationToken = default) =>
+        ReadCollision(
+            PakAssetType.EnvCellTopology,
+            sourceFileId,
+            static (bytes, token) =>
+                FlatCollisionAssetSerializer.DeserializeEnvCellTopology(
+                    bytes,
+                    token),
+            cancellationToken);
+
+    private PreparedCollisionReadResult<T> ReadCollision<T>(
+        PakAssetType type,
+        uint sourceFileId,
+        Func<byte[], CancellationToken, T> deserialize,
+        CancellationToken cancellationToken)
+        where T : class
+    {
+        PreparedCollisionTypeContract.Validate(type);
+        cancellationToken.ThrowIfCancellationRequested();
+        Interlocked.Increment(ref _collisionReads);
+
+        ulong key = PakKey.Compose(type, sourceFileId);
+        PakObjectReadStatus status =
+            _reader.ReadBlobBytes(key, out byte[]? bytes);
+        cancellationToken.ThrowIfCancellationRequested();
+        if (status == PakObjectReadStatus.Missing)
+        {
+            Interlocked.Increment(ref _collisionMissing);
+            return PreparedCollisionReadResult<T>.Missing;
+        }
+        if (status == PakObjectReadStatus.Corrupt || bytes is null)
+        {
+            Interlocked.Increment(ref _collisionCorrupt);
+            return PreparedCollisionReadResult<T>.Corrupt;
+        }
+
+        try
+        {
+            T data = deserialize(bytes, cancellationToken);
+            cancellationToken.ThrowIfCancellationRequested();
+            Interlocked.Increment(ref _collisionLoaded);
+            return PreparedCollisionReadResult<T>.Loaded(data);
+        }
+        catch (OperationCanceledException)
+        {
+            throw;
+        }
+        catch (Exception exception)
+        {
+            _reader.MarkPayloadCorrupt(
+                key,
+                $"collision deserialization failed despite matching CRC: " +
+                $"{exception.GetType().Name}: {exception.Message}");
+            Interlocked.Increment(ref _collisionCorrupt);
+            return PreparedCollisionReadResult<T>.Corrupt;
+        }
+    }
+}
diff --git a/src/AcDream.Content/Pak/PakFormat.cs b/src/AcDream.Content/Pak/PakFormat.cs
index 94e2d9a1..4ccb2d6f 100644
--- a/src/AcDream.Content/Pak/PakFormat.cs
+++ b/src/AcDream.Content/Pak/PakFormat.cs
@@ -20,10 +20,11 @@ public static class PakFormat {
     /// Identity of the bake algorithm that produced the payloads. Version 2
     /// introduced content-identity EnvCell blobs with ordinary TOC aliases;
     /// version 3 embeds exact render-pass translucency in each texture batch
-    /// so production never rebuilds surface metadata from live DAT.
+    /// so production never rebuilds surface metadata from live DAT. Version 4
+    /// adds complete immutable flat collision and EnvCell-topology payloads.
     /// The binary format remains version 1.
     /// </summary>
-    public const uint CurrentBakeToolVersion = 3;
+    public const uint CurrentBakeToolVersion = 4;
 }
 
 /// <summary>
diff --git a/src/AcDream.Content/Pak/PakKey.cs b/src/AcDream.Content/Pak/PakKey.cs
index da1a8753..8d98d460 100644
--- a/src/AcDream.Content/Pak/PakKey.cs
+++ b/src/AcDream.Content/Pak/PakKey.cs
@@ -11,6 +11,10 @@ public enum PakAssetType : byte {
     GfxObjMesh = 1,
     SetupMesh = 2,
     EnvCellMesh = 3,
+    GfxObjCollision = 4,
+    SetupCollision = 5,
+    CellStructureCollision = 6,
+    EnvCellTopology = 7,
 }
 
 /// <summary>
diff --git a/src/AcDream.Content/Pak/PakReader.cs b/src/AcDream.Content/Pak/PakReader.cs
index ef636757..c6767e44 100644
--- a/src/AcDream.Content/Pak/PakReader.cs
+++ b/src/AcDream.Content/Pak/PakReader.cs
@@ -145,6 +145,44 @@ public sealed class PakReader : IDisposable {
         ulong key,
         out ObjectMeshData? data) {
         data = null;
+        PakAssetType type = PakKey.Decompose(key).Type;
+        if (type is not (
+            PakAssetType.GfxObjMesh or
+            PakAssetType.SetupMesh or
+            PakAssetType.EnvCellMesh)) {
+            return PakObjectReadStatus.Missing;
+        }
+
+        PakObjectReadStatus status = ReadBlobBytes(key, out byte[]? bytes);
+        if (status != PakObjectReadStatus.Loaded || bytes is null)
+            return status;
+
+        try {
+            data = ObjectMeshDataSerializer.Read(bytes);
+            return PakObjectReadStatus.Loaded;
+        }
+        catch (Exception ex) {
+            // Structurally malformed blob behind a valid CRC (bake-side bug or
+            // a tamper that recomputed the CRC). External-file input: demote
+            // to missing, log once — never propagate from a lookup.
+            data = null;
+            MarkPayloadCorrupt(
+                key,
+                $"deserialization failed despite matching CRC: " +
+                $"{ex.GetType().Name}: {ex.Message}");
+            return PakObjectReadStatus.Corrupt;
+        }
+    }
+
+    /// <summary>
+    /// Copies and CRC-verifies one typed blob without interpreting its schema.
+    /// Content-layer typed sources deserialize the returned bytes and call
+    /// <see cref="MarkPayloadCorrupt"/> on structural failure.
+    /// </summary>
+    internal PakObjectReadStatus ReadBlobBytes(
+        ulong key,
+        out byte[]? bytes) {
+        bytes = null;
         int index = BinarySearch(key);
         if (index < 0) return PakObjectReadStatus.Missing;
 
@@ -156,7 +194,7 @@ public sealed class PakReader : IDisposable {
         // Single pass (review finding 4): ONE copy out of the map; CRC and
         // deserialization both run over this same buffer.
         ref readonly var entry = ref _toc[index];
-        var bytes = new byte[entry.Length];
+        bytes = new byte[entry.Length];
         _accessor.ReadArray((long)entry.Offset, bytes, 0, (int)entry.Length);
 
         if (!judged) {
@@ -164,24 +202,21 @@ public sealed class PakReader : IDisposable {
             if (actualCrc != entry.Crc32) {
                 _entryVerdictByTocIndex[index] = 0;
                 LogCorruptionOnce(index, $"crc mismatch (expected 0x{entry.Crc32:X8}, got 0x{actualCrc:X8})");
+                bytes = null;
                 return PakObjectReadStatus.Corrupt;
             }
             _entryVerdictByTocIndex[index] = 1;
         }
 
-        try {
-            data = ObjectMeshDataSerializer.Read(bytes);
-            return PakObjectReadStatus.Loaded;
-        }
-        catch (Exception ex) {
-            // Structurally malformed blob behind a valid CRC (bake-side bug or
-            // a tamper that recomputed the CRC). External-file input: demote
-            // to missing, log once — never propagate from a lookup.
-            data = null;
-            _entryVerdictByTocIndex[index] = 0;
-            LogCorruptionOnce(index, $"deserialization failed despite matching CRC: {ex.GetType().Name}: {ex.Message}");
-            return PakObjectReadStatus.Corrupt;
-        }
+        return PakObjectReadStatus.Loaded;
+    }
+
+    internal void MarkPayloadCorrupt(ulong key, string reason) {
+        int index = BinarySearch(key);
+        if (index < 0)
+            return;
+        _entryVerdictByTocIndex[index] = 0;
+        LogCorruptionOnce(index, reason);
     }
 
     /// <summary>Returns the blob's file offset for alignment assertions in tests.</summary>
@@ -198,6 +233,20 @@ public sealed class PakReader : IDisposable {
         return _toc[index];
     }
 
+    /// <summary>
+    /// Counts one typed catalog partition without touching payload bytes.
+    /// Used by the offline publisher to prove package completeness.
+    /// </summary>
+    public int CountEntries(PakAssetType type) {
+        byte rawType = (byte)type;
+        int count = 0;
+        for (int i = 0; i < _toc.Length; i++) {
+            if ((byte)(_toc[i].Key >> 56) == rawType)
+                count++;
+        }
+        return count;
+    }
+
     /// <summary>
     /// Validates the complete immutable TOC before an offline bake publishes
     /// it. This is intentionally stricter than runtime lookup: key order and
diff --git a/src/AcDream.Content/Pak/PakWriter.cs b/src/AcDream.Content/Pak/PakWriter.cs
index b5316eb3..672bbfcd 100644
--- a/src/AcDream.Content/Pak/PakWriter.cs
+++ b/src/AcDream.Content/Pak/PakWriter.cs
@@ -46,28 +46,51 @@ public sealed class PakWriter : IDisposable {
     /// </summary>
     public void AddBlob(ulong key, ObjectMeshData data) {
         ThrowIfFinished();
-        if (!_seenKeys.Add(key)) {
-            throw new ArgumentException($"duplicate pak key 0x{key:X16}", nameof(key));
-        }
+        ReserveKey(key);
 
-        long offset = _stream.Position;
         using var ms = new MemoryStream();
         ObjectMeshDataSerializer.Write(data, ms);
         var bytes = ms.ToArray();
+        AddReservedBlob(key, bytes);
+    }
 
+    /// <summary>
+    /// Adds an already serialized immutable payload. This is the package seam
+    /// used by typed non-render assets such as flat collision records.
+    /// </summary>
+    public void AddBlob(ulong key, ReadOnlySpan<byte> bytes) {
+        ThrowIfFinished();
+        ReserveKey(key);
+        AddReservedBlob(key, bytes);
+    }
+
+    private void AddReservedBlob(ulong key, ReadOnlySpan<byte> bytes) {
+        if ((ulong)bytes.Length > uint.MaxValue) {
+            throw new ArgumentException(
+                "one pak payload cannot exceed UInt32.MaxValue bytes",
+                nameof(bytes));
+        }
+
+        long offset = _stream.Position;
         _stream.Write(bytes);
         PadToAlignment();
 
         var receipt = new PakTocEntry {
             Key = key,
             Offset = (ulong)offset,
-            Length = (uint)bytes.Length,
+            Length = checked((uint)bytes.Length),
             Crc32 = Content.Pak.Crc32.Compute(bytes),
         };
         _tocEntries.Add(receipt);
         _receiptByKey.Add(key, receipt);
     }
 
+    private void ReserveKey(ulong key) {
+        if (!_seenKeys.Add(key)) {
+            throw new ArgumentException($"duplicate pak key 0x{key:X16}", nameof(key));
+        }
+    }
+
     /// <summary>
     /// Adds a second independently addressable key for an existing physical
     /// blob. The alias receives a normal TOC row with the source blob's exact
diff --git a/src/AcDream.Core/Physics/FlatCollisionAssetBuilder.cs b/src/AcDream.Core/Physics/FlatCollisionAssetBuilder.cs
index d8e75dc0..4c0ec536 100644
--- a/src/AcDream.Core/Physics/FlatCollisionAssetBuilder.cs
+++ b/src/AcDream.Core/Physics/FlatCollisionAssetBuilder.cs
@@ -1,6 +1,8 @@
 using System.Collections.Immutable;
 using System.Numerics;
 using System.Runtime.CompilerServices;
+using DatReaderWriter.DBObjs;
+using DatReaderWriter.Enums;
 using DatReaderWriter.Types;
 
 namespace AcDream.Core.Physics;
@@ -15,6 +17,13 @@ namespace AcDream.Core.Physics;
 /// </summary>
 public static class FlatCollisionAssetBuilder
 {
+    private static FlatPhysicsBsp EmptyPhysicsBsp() =>
+        new(
+            -1,
+            ImmutableArray<FlatPhysicsBspNode>.Empty,
+            ImmutableArray<int>.Empty,
+            FlatPolygonTable.Empty);
+
     public static FlatPhysicsBsp FlattenPhysicsBsp(
         PhysicsBSPNode? root,
         IReadOnlyDictionary<ushort, ResolvedPolygon> resolved)
@@ -270,6 +279,53 @@ public static class FlatCollisionAssetBuilder
             source.StepDownHeight);
     }
 
+    /// <summary>
+    /// Prepares the exact Setup collision fields used by
+    /// <see cref="PhysicsDataCache.CacheSetup"/> without retaining the parsed
+    /// DAT object. Source list order and every float bit are preserved.
+    /// </summary>
+    public static FlatSetupCollision FlattenSetup(Setup source)
+    {
+        ArgumentNullException.ThrowIfNull(source);
+
+        var cylinders = ImmutableArray.CreateBuilder<FlatCollisionCylinder>(
+            source.CylSpheres?.Count ?? 0);
+        if (source.CylSpheres is not null)
+        {
+            foreach (CylSphere cylinder in source.CylSpheres)
+            {
+                if (cylinder is null)
+                    throw new InvalidDataException("Setup cylinder row is null.");
+                cylinders.Add(new FlatCollisionCylinder(
+                    cylinder.Origin,
+                    cylinder.Radius,
+                    cylinder.Height));
+            }
+        }
+
+        var spheres = ImmutableArray.CreateBuilder<FlatCollisionSphere>(
+            source.Spheres?.Count ?? 0);
+        if (source.Spheres is not null)
+        {
+            foreach (Sphere sphere in source.Spheres)
+            {
+                if (sphere is null)
+                    throw new InvalidDataException("Setup sphere row is null.");
+                spheres.Add(new FlatCollisionSphere(
+                    sphere.Origin,
+                    sphere.Radius));
+            }
+        }
+
+        return new FlatSetupCollision(
+            cylinders.MoveToImmutable(),
+            spheres.MoveToImmutable(),
+            source.Height,
+            source.Radius,
+            source.StepUpHeight,
+            source.StepDownHeight);
+    }
+
     public static FlatGfxObjCollisionAsset FlattenGfxObj(
         GfxObjPhysics source,
         GfxObjVisualBounds? visualBounds = null)
@@ -297,6 +353,139 @@ public static class FlatCollisionAssetBuilder
             flatVisualBounds);
     }
 
+    /// <summary>
+    /// Prepares one parsed GfxObj and drops the source graph. Objects without
+    /// a retail physics BSP still retain their visual bounds because the
+    /// current runtime uses those bounds as its collision fallback.
+    /// </summary>
+    public static FlatGfxObjCollisionAsset FlattenGfxObj(GfxObj source)
+    {
+        ArgumentNullException.ThrowIfNull(source);
+
+        GfxObjVisualBounds? visualBounds = source.VertexArray is null
+            ? null
+            : PhysicsDataCache.ComputeVisualBounds(source.VertexArray);
+        FlatGfxObjVisualBounds? flatVisualBounds = visualBounds is null
+            ? null
+            : new FlatGfxObjVisualBounds(
+                visualBounds.Min,
+                visualBounds.Max,
+                visualBounds.Center,
+                visualBounds.Radius,
+                visualBounds.HalfExtents);
+
+        bool hasPhysics =
+            source.Flags.HasFlag(GfxObjFlags.HasPhysics)
+            && source.PhysicsBSP?.Root is not null
+            && source.VertexArray is not null;
+        if (!hasPhysics)
+        {
+            return new FlatGfxObjCollisionAsset(
+                EmptyPhysicsBsp(),
+                null,
+                flatVisualBounds);
+        }
+
+        Dictionary<ushort, ResolvedPolygon> resolved =
+            PhysicsDataCache.ResolvePolygons(
+                source.PhysicsPolygons,
+                source.VertexArray!);
+        Sphere boundingSphere = source.PhysicsBSP!.Root!.BoundingSphere
+            ?? throw new InvalidDataException(
+                "GfxObj physics BSP root has no bounding sphere.");
+
+        return new FlatGfxObjCollisionAsset(
+            FlattenPhysicsBsp(source.PhysicsBSP.Root, resolved),
+            new FlatCollisionSphere(
+                boundingSphere.Origin,
+                boundingSphere.Radius),
+            flatVisualBounds);
+    }
+
+    /// <summary>
+    /// Prepares reusable CellStruct collision geometry independently of any
+    /// EnvCell placement or topology.
+    /// </summary>
+    public static FlatCellStructureCollisionAsset FlattenCellStructure(
+        CellStruct source)
+    {
+        ArgumentNullException.ThrowIfNull(source);
+
+        FlatPhysicsBsp physicsBsp;
+        if (source.PhysicsBSP?.Root is null)
+        {
+            physicsBsp = EmptyPhysicsBsp();
+        }
+        else
+        {
+            Dictionary<ushort, ResolvedPolygon> resolved =
+                PhysicsDataCache.ResolvePolygons(
+                    source.PhysicsPolygons,
+                    source.VertexArray);
+            physicsBsp = FlattenPhysicsBsp(
+                source.PhysicsBSP.Root,
+                resolved);
+        }
+
+        Dictionary<ushort, ResolvedPolygon> portalResolved =
+            PhysicsDataCache.ResolvePolygons(
+                source.Polygons,
+                source.VertexArray);
+        return new FlatCellStructureCollisionAsset(
+            physicsBsp,
+            FlattenCellContainmentBsp(source.CellBSP?.Root),
+            FlattenPolygonTable(portalResolved));
+    }
+
+    /// <summary>
+    /// Prepares the per-cell portion of collision publication. Other-cell IDs
+    /// are expanded with the owning landblock exactly as
+    /// <see cref="PhysicsDataCache.CacheCellStruct"/> does.
+    /// </summary>
+    public static FlatEnvCellTopology FlattenEnvCellTopology(
+        uint envCellId,
+        EnvCell source,
+        FlatPolygonTable portalPolygons)
+    {
+        ArgumentNullException.ThrowIfNull(source);
+        ArgumentNullException.ThrowIfNull(portalPolygons);
+
+        var portals = ImmutableArray.CreateBuilder<FlatEnvCellPortal>(
+            source.CellPortals.Count);
+        foreach (CellPortal portal in source.CellPortals)
+        {
+            ushort polygonId = portal.PolygonId;
+            if (!portalPolygons.TryFindPolygonIndex(
+                    polygonId,
+                    out int polygonIndex))
+            {
+                throw new InvalidDataException(
+                    $"EnvCell 0x{envCellId:X8} portal references missing " +
+                    $"polygon 0x{polygonId:X4}.");
+            }
+
+            portals.Add(new FlatEnvCellPortal(
+                portal.OtherCellId,
+                polygonId,
+                (ushort)portal.Flags,
+                polygonIndex));
+        }
+
+        uint prefix = envCellId & 0xFFFF_0000u;
+        uint[] visibleIds = source.VisibleCells is null
+            ? []
+            : source.VisibleCells
+                .Select(id => prefix | id)
+                .Distinct()
+                .Order()
+                .ToArray();
+
+        return new FlatEnvCellTopology(
+            portals.MoveToImmutable(),
+            ImmutableArray.Create(visibleIds),
+            source.Flags.HasFlag(EnvCellFlags.SeenOutside));
+    }
+
     public static FlatCellCollisionAsset FlattenCell(CellPhysics source)
     {
         ArgumentNullException.ThrowIfNull(source);
@@ -310,9 +499,31 @@ public static class FlatCollisionAssetBuilder
             source.PortalPolygons
             ?? new Dictionary<ushort, ResolvedPolygon>());
 
-        var portals = ImmutableArray.CreateBuilder<FlatEnvCellPortal>(
-            source.Portals.Count);
-        foreach (PortalInfo portal in source.Portals)
+        FlatEnvCellTopology topology = FlattenEnvCellTopology(
+            source.Portals,
+            source.VisibleCellIds,
+            source.SeenOutside,
+            portalPolygons);
+        var structure = new FlatCellStructureCollisionAsset(
+            physicsBsp,
+            containmentBsp,
+            portalPolygons);
+        return new FlatCellCollisionAsset(structure, topology);
+    }
+
+    public static FlatEnvCellTopology FlattenEnvCellTopology(
+        IReadOnlyList<PortalInfo> portals,
+        IEnumerable<uint> visibleCellIds,
+        bool seenOutside,
+        FlatPolygonTable portalPolygons)
+    {
+        ArgumentNullException.ThrowIfNull(portals);
+        ArgumentNullException.ThrowIfNull(visibleCellIds);
+        ArgumentNullException.ThrowIfNull(portalPolygons);
+
+        var flatPortals = ImmutableArray.CreateBuilder<FlatEnvCellPortal>(
+            portals.Count);
+        foreach (PortalInfo portal in portals)
         {
             if (!portalPolygons.TryFindPolygonIndex(
                     portal.PolygonId,
@@ -323,24 +534,21 @@ public static class FlatCollisionAssetBuilder
                     $"0x{portal.PolygonId:X4}.");
             }
 
-            portals.Add(new FlatEnvCellPortal(
+            flatPortals.Add(new FlatEnvCellPortal(
                 portal.OtherCellId,
                 portal.PolygonId,
                 portal.Flags,
                 polygonIndex));
         }
 
-        uint[] visibleIds = source.VisibleCellIds.ToArray();
-        Array.Sort(visibleIds);
-        var topology = new FlatEnvCellTopology(
-            portals.MoveToImmutable(),
+        uint[] visibleIds = visibleCellIds
+            .Distinct()
+            .Order()
+            .ToArray();
+        return new FlatEnvCellTopology(
+            flatPortals.MoveToImmutable(),
             ImmutableArray.Create(visibleIds),
-            source.SeenOutside);
-        var structure = new FlatCellStructureCollisionAsset(
-            physicsBsp,
-            containmentBsp,
-            portalPolygons);
-        return new FlatCellCollisionAsset(structure, topology);
+            seenOutside);
     }
 
     private static void AttachChild(
diff --git a/src/AcDream.Core/Physics/PhysicsDataCache.cs b/src/AcDream.Core/Physics/PhysicsDataCache.cs
index f90808fa..5772f361 100644
--- a/src/AcDream.Core/Physics/PhysicsDataCache.cs
+++ b/src/AcDream.Core/Physics/PhysicsDataCache.cs
@@ -104,7 +104,7 @@ public sealed class PhysicsDataCache
     /// Used as a fallback collision shape for entities whose Setup has no
     /// physics data — we approximate collision using the visual extent.
     /// </summary>
-    private static GfxObjVisualBounds ComputeVisualBounds(VertexArray vertexArray)
+    internal static GfxObjVisualBounds ComputeVisualBounds(VertexArray vertexArray)
     {
         if (vertexArray.Vertices == null || vertexArray.Vertices.Count == 0)
         {
diff --git a/tests/AcDream.Bake.Tests/BakeDeterminismTests.cs b/tests/AcDream.Bake.Tests/BakeDeterminismTests.cs
index f7e5b4bb..894e742f 100644
--- a/tests/AcDream.Bake.Tests/BakeDeterminismTests.cs
+++ b/tests/AcDream.Bake.Tests/BakeDeterminismTests.cs
@@ -76,6 +76,43 @@ public sealed class BakeDeterminismTests : IDisposable {
             $"pak sizes differ between runs: {bytesA.Length} vs {bytesB.Length} bytes");
         Assert.True(bytesA.AsSpan().SequenceEqual(bytesB),
             "two bakes of the same id set produced different bytes — the sorted-batching determinism guarantee is broken");
+        using var reader = new PakReader(pathA);
+        foreach (uint gfxId in new[]
+        {
+            0x01000001u,
+            0x010002B4u,
+            0x010008A8u,
+            0x010014C3u,
+        })
+        {
+            Assert.True(reader.ContainsKey(PakKey.Compose(
+                PakAssetType.GfxObjCollision,
+                gfxId)));
+        }
+        foreach (uint setupId in new[]
+        {
+            0x02000001u,
+            0x020019FFu,
+            0x020005D8u,
+        })
+        {
+            Assert.True(reader.ContainsKey(PakKey.Compose(
+                PakAssetType.SetupCollision,
+                setupId)));
+        }
+        foreach (uint cellId in new[]
+        {
+            0xA9B40100u,
+            0xA9B40101u,
+        })
+        {
+            Assert.True(reader.ContainsKey(PakKey.Compose(
+                PakAssetType.CellStructureCollision,
+                cellId)));
+            Assert.True(reader.ContainsKey(PakKey.Compose(
+                PakAssetType.EnvCellTopology,
+                cellId)));
+        }
     }
 
     [Fact]
@@ -111,7 +148,11 @@ public sealed class BakeDeterminismTests : IDisposable {
         Assert.Equal(8, reportA.EnvCellKeys);
         Assert.Equal(1, reportA.UniqueEnvCellGeometries);
         Assert.Equal(7, reportA.EnvCellAliases);
-        Assert.Equal(1, reportA.PhysicalBlobs);
+        Assert.Equal(8, reportA.CellStructureCollisionKeys);
+        Assert.Equal(1, reportA.UniqueCellStructureCollisions);
+        Assert.Equal(7, reportA.CellStructureCollisionAliases);
+        Assert.Equal(8, reportA.EnvCellTopologyKeys);
+        Assert.Equal(10, reportA.PhysicalBlobs);
         Assert.Equal(reportA.TotalKeys, reportB.TotalKeys);
         Assert.True(File.ReadAllBytes(pathA).AsSpan().SequenceEqual(File.ReadAllBytes(pathB)));
 
@@ -124,6 +165,27 @@ public sealed class BakeDeterminismTests : IDisposable {
         Assert.All(receipts, receipt => Assert.Equal(receipts[0].Length, receipt.Length));
         Assert.All(receipts, receipt => Assert.Equal(receipts[0].Crc32, receipt.Crc32));
 
+        var collisionReceipts = ids
+            .Select(id => reader.GetTocEntryForTest(
+                PakKey.Compose(PakAssetType.CellStructureCollision, id)))
+            .ToArray();
+        Assert.All(
+            collisionReceipts,
+            receipt => Assert.Equal(
+                collisionReceipts[0].Offset,
+                receipt.Offset));
+        Assert.All(
+            collisionReceipts,
+            receipt => Assert.Equal(
+                collisionReceipts[0].Length,
+                receipt.Length));
+        Assert.Equal(
+            ids.Count,
+            ids.Select(id => reader.GetTocEntryForTest(
+                    PakKey.Compose(PakAssetType.EnvCellTopology, id)).Offset)
+                .Distinct()
+                .Count());
+
         Assert.True(
             reader.TryReadObjectMeshData(
                 PakKey.Compose(PakAssetType.EnvCellMesh, ids.Min()),
@@ -132,4 +194,34 @@ public sealed class BakeDeterminismTests : IDisposable {
         Assert.Equal(0xE000_0000_0000_0000UL,
             geometry.ObjectId & 0xF000_0000_0000_0000UL);
     }
+
+    [Fact]
+    public void Bake_CancellationCannotReplaceLastGoodPackage()
+    {
+        string? datDir = ResolveDatDir();
+        if (datDir is null)
+            return;
+
+        string destination = NewTempPakPath();
+        byte[] lastGood = [0x41, 0x43, 0x50, 0x4B, 1, 2, 3, 4];
+        File.WriteAllBytes(destination, lastGood);
+        using var cancellation = new CancellationTokenSource();
+        cancellation.CancelAfter(TimeSpan.FromMilliseconds(20));
+
+        Assert.Throws<OperationCanceledException>(
+            () => BakeRunner.RunDetailed(
+                new BakeOptions
+                {
+                    DatDir = datDir,
+                    OutPath = destination,
+                    Threads = 2,
+                    CancellationToken = cancellation.Token,
+                }));
+
+        Assert.Equal(lastGood, File.ReadAllBytes(destination));
+        Assert.Empty(
+            Directory.EnumerateFiles(
+                Path.GetDirectoryName(destination)!,
+                $".{Path.GetFileName(destination)}.*.tmp"));
+    }
 }
diff --git a/tests/AcDream.Bake.Tests/BakeOutputTransactionTests.cs b/tests/AcDream.Bake.Tests/BakeOutputTransactionTests.cs
index 80963cb4..4d397817 100644
--- a/tests/AcDream.Bake.Tests/BakeOutputTransactionTests.cs
+++ b/tests/AcDream.Bake.Tests/BakeOutputTransactionTests.cs
@@ -154,6 +154,33 @@ public sealed class BakeOutputTransactionTests : IDisposable
             () => BakeArtifactValidator.Validate(pak, expected, expectedTocCount: 1));
     }
 
+    [Fact]
+    public void ArtifactValidator_RejectsIncompleteTypedCatalog()
+    {
+        string pak = Path.Combine(_directory, "typed-content.pak");
+        var expected = Header();
+        using (var writer = new PakWriter(pak, expected))
+        {
+            writer.AddBlob(
+                PakKey.Compose(PakAssetType.GfxObjMesh, 1),
+                new ObjectMeshData { ObjectId = 1 });
+            writer.Finish();
+        }
+
+        var expectedTypes = new Dictionary<PakAssetType, int>
+        {
+            [PakAssetType.GfxObjMesh] = 1,
+            [PakAssetType.GfxObjCollision] = 1,
+        };
+        InvalidDataException exception = Assert.Throws<InvalidDataException>(
+            () => BakeArtifactValidator.Validate(
+                pak,
+                expected,
+                expectedTocCount: 1,
+                expectedTypeCounts: expectedTypes));
+        Assert.Contains("GfxObjCollision", exception.Message);
+    }
+
     private PakHeader Header() =>
         new()
         {
diff --git a/tests/AcDream.Bake.Tests/ExactPayloadAliasCatalogTests.cs b/tests/AcDream.Bake.Tests/ExactPayloadAliasCatalogTests.cs
new file mode 100644
index 00000000..0b30cd57
--- /dev/null
+++ b/tests/AcDream.Bake.Tests/ExactPayloadAliasCatalogTests.cs
@@ -0,0 +1,24 @@
+namespace AcDream.Bake.Tests;
+
+public sealed class ExactPayloadAliasCatalogTests
+{
+    [Fact]
+    public void AliasRequiresCompleteByteEquality()
+    {
+        var catalog = new ExactPayloadAliasCatalog();
+        byte[] primary = [1, 2, 3, 4, 5];
+        catalog.Add(0x1234UL, primary);
+
+        Assert.True(catalog.TryFind(
+            [1, 2, 3, 4, 5],
+            out ulong primaryKey));
+        Assert.Equal(0x1234UL, primaryKey);
+
+        Assert.False(catalog.TryFind(
+            [1, 2, 3, 4, 4],
+            out _));
+        Assert.False(catalog.TryFind(
+            [1, 2, 3, 4, 5, 0],
+            out _));
+    }
+}
diff --git a/tests/AcDream.Content.Tests/FlatCollisionAssetSerializerTests.cs b/tests/AcDream.Content.Tests/FlatCollisionAssetSerializerTests.cs
new file mode 100644
index 00000000..c5bf85e1
--- /dev/null
+++ b/tests/AcDream.Content.Tests/FlatCollisionAssetSerializerTests.cs
@@ -0,0 +1,512 @@
+using System.Collections.Immutable;
+using System.Numerics;
+using AcDream.Content.Pak;
+using AcDream.Core.Physics;
+using DatReaderWriter.Enums;
+
+namespace AcDream.Content.Tests;
+
+public sealed class FlatCollisionAssetSerializerTests : IDisposable
+{
+    private static readonly PreparedAssetCatalogIdentity Identity =
+        new(10, 20, 30, 40, PakFormat.CurrentBakeToolVersion);
+
+    private readonly List<string> _paths = [];
+
+    [Fact]
+    public void EveryPayload_RoundTripsToByteIdenticalRepresentation()
+    {
+        FlatGfxObjCollisionAsset gfx = GfxAsset();
+        FlatSetupCollision setup = SetupAsset();
+        FlatCellStructureCollisionAsset structure = CellStructureAsset();
+        FlatEnvCellTopology topology = TopologyAsset();
+
+        byte[] gfxBytes = FlatCollisionAssetSerializer.Serialize(gfx);
+        byte[] setupBytes = FlatCollisionAssetSerializer.Serialize(setup);
+        byte[] structureBytes =
+            FlatCollisionAssetSerializer.Serialize(structure);
+        byte[] topologyBytes =
+            FlatCollisionAssetSerializer.Serialize(topology);
+
+        FlatGfxObjCollisionAsset readGfx =
+            FlatCollisionAssetSerializer.DeserializeGfxObj(gfxBytes);
+        FlatSetupCollision readSetup =
+            FlatCollisionAssetSerializer.DeserializeSetup(setupBytes);
+        FlatCellStructureCollisionAsset readStructure =
+            FlatCollisionAssetSerializer.DeserializeCellStructure(
+                structureBytes);
+        FlatEnvCellTopology readTopology =
+            FlatCollisionAssetSerializer.DeserializeEnvCellTopology(
+                topologyBytes);
+
+        Assert.Equal(
+            gfxBytes,
+            FlatCollisionAssetSerializer.Serialize(readGfx));
+        Assert.Equal(
+            setupBytes,
+            FlatCollisionAssetSerializer.Serialize(readSetup));
+        Assert.Equal(
+            structureBytes,
+            FlatCollisionAssetSerializer.Serialize(readStructure));
+        Assert.Equal(
+            topologyBytes,
+            FlatCollisionAssetSerializer.Serialize(readTopology));
+
+        AssertFloatBits(
+            gfx.VisualBounds!.Value.Radius,
+            readGfx.VisualBounds!.Value.Radius);
+        AssertFloatBits(
+            setup.StepDownHeight,
+            readSetup.StepDownHeight);
+        AssertFloatBits(
+            structure.PhysicsBsp.Nodes[0].SplittingPlane.D,
+            readStructure.PhysicsBsp.Nodes[0].SplittingPlane.D);
+        Assert.Equal(
+            topology.VisibleCellIds.AsEnumerable(),
+            readTopology.VisibleCellIds.AsEnumerable());
+    }
+
+    [Fact]
+    public void Encoding_IsLittleEndianAndPreservesSpecialFloatBits()
+    {
+        float special = BitConverter.Int32BitsToSingle(
+            unchecked((int)0xFFC0_1234u));
+        var setup = new FlatSetupCollision(
+            ImmutableArray<FlatCollisionCylinder>.Empty,
+            ImmutableArray<FlatCollisionSphere>.Empty,
+            special,
+            -0f,
+            float.PositiveInfinity,
+            float.NegativeInfinity);
+
+        byte[] bytes = FlatCollisionAssetSerializer.Serialize(setup);
+
+        // Header is "ACCL", kind=Setup, schema=1, reserved=0. Counts follow,
+        // then the exact little-endian IEEE-754 bits for Height.
+        Assert.Equal(
+            new byte[]
+            {
+                0x41, 0x43, 0x43, 0x4C,
+                0x02, 0x01, 0x00, 0x00,
+            },
+            bytes[..8]);
+        Assert.Equal(
+            new byte[] { 0x34, 0x12, 0xC0, 0xFF },
+            bytes[16..20]);
+
+        FlatSetupCollision read =
+            FlatCollisionAssetSerializer.DeserializeSetup(bytes);
+        AssertFloatBits(special, read.Height);
+        AssertFloatBits(-0f, read.Radius);
+        AssertFloatBits(float.PositiveInfinity, read.StepUpHeight);
+        AssertFloatBits(float.NegativeInfinity, read.StepDownHeight);
+    }
+
+    [Fact]
+    public void Readers_RejectWrongKindTruncationTrailingAndInvalidCounts()
+    {
+        byte[] setup = FlatCollisionAssetSerializer.Serialize(SetupAsset());
+
+        Assert.Throws<InvalidDataException>(
+            () => FlatCollisionAssetSerializer.DeserializeGfxObj(setup));
+
+        for (int length = 0; length < setup.Length; length++)
+        {
+            Assert.ThrowsAny<Exception>(
+                () => FlatCollisionAssetSerializer.DeserializeSetup(
+                    setup.AsSpan(0, length)));
+        }
+
+        Assert.Throws<InvalidDataException>(
+            () => FlatCollisionAssetSerializer.DeserializeSetup(
+                [.. setup, 0x00]));
+
+        byte[] negativeCount = (byte[])setup.Clone();
+        negativeCount[8] = 0xFF;
+        negativeCount[9] = 0xFF;
+        negativeCount[10] = 0xFF;
+        negativeCount[11] = 0xFF;
+        Assert.Throws<InvalidDataException>(
+            () => FlatCollisionAssetSerializer.DeserializeSetup(
+                negativeCount));
+
+        byte[] impossibleCombinedCounts = (byte[])setup.Clone();
+        impossibleCombinedCounts[8] = 0x03;
+        impossibleCombinedCounts[12] = 0x03;
+        Assert.Throws<InvalidDataException>(
+            () => FlatCollisionAssetSerializer.DeserializeSetup(
+                impossibleCombinedCounts));
+    }
+
+    [Fact]
+    public void SerializeAndDeserialize_PropagatePreCancellation()
+    {
+        using var cancellation = new CancellationTokenSource();
+        cancellation.Cancel();
+
+        Assert.Throws<OperationCanceledException>(
+            () => FlatCollisionAssetSerializer.Serialize(
+                GfxAsset(),
+                cancellation.Token));
+        byte[] bytes =
+            FlatCollisionAssetSerializer.Serialize(GfxAsset());
+        Assert.Throws<OperationCanceledException>(
+            () => FlatCollisionAssetSerializer.DeserializeGfxObj(
+                bytes,
+                cancellation.Token));
+    }
+
+    [Fact]
+    public void PreparedSource_ReadsAllCollisionKindsThroughSamePackageOwner()
+    {
+        const uint gfxId = 0x0100_0001u;
+        const uint setupId = 0x0200_0001u;
+        const uint cellId = 0xA9B4_0101u;
+        string path = NewPath();
+        using (var writer = new PakWriter(path, Header()))
+        {
+            writer.AddBlob(
+                PakKey.Compose(PakAssetType.GfxObjCollision, gfxId),
+                FlatCollisionAssetSerializer.Serialize(GfxAsset()));
+            writer.AddBlob(
+                PakKey.Compose(PakAssetType.SetupCollision, setupId),
+                FlatCollisionAssetSerializer.Serialize(SetupAsset()));
+            writer.AddBlob(
+                PakKey.Compose(
+                    PakAssetType.CellStructureCollision,
+                    cellId),
+                FlatCollisionAssetSerializer.Serialize(CellStructureAsset()));
+            writer.AddBlob(
+                PakKey.Compose(PakAssetType.EnvCellTopology, cellId),
+                FlatCollisionAssetSerializer.Serialize(TopologyAsset()));
+            writer.Finish();
+        }
+
+        using var owner = new PakPreparedAssetSource(path, Identity);
+        IPreparedAssetSource renderSource = owner;
+        IPreparedCollisionSource collisionSource = owner;
+
+        Assert.Equal(
+            PreparedAssetPresence.Available,
+            collisionSource.ProbeCollision(
+                PakAssetType.GfxObjCollision,
+                gfxId));
+        Assert.Equal(
+            PreparedAssetReadStatus.Loaded,
+            collisionSource.ReadGfxObjCollision(gfxId).Status);
+        Assert.Equal(
+            PreparedAssetReadStatus.Loaded,
+            collisionSource.ReadSetupCollision(setupId).Status);
+        Assert.Equal(
+            PreparedAssetReadStatus.Loaded,
+            collisionSource.ReadCellStructureCollision(cellId).Status);
+        Assert.Equal(
+            PreparedAssetReadStatus.Loaded,
+            collisionSource.ReadEnvCellTopology(cellId).Status);
+        Assert.Equal(4, collisionSource.CollisionStats.Loaded);
+        Assert.Equal(0, renderSource.Stats.Reads);
+        Assert.Equal(new FileInfo(path).Length, renderSource.MappedVirtualBytes);
+
+        Assert.Throws<ArgumentOutOfRangeException>(
+            () => renderSource.Probe(
+                PakAssetType.GfxObjCollision,
+                gfxId));
+        Assert.Throws<ArgumentOutOfRangeException>(
+            () => collisionSource.ProbeCollision(
+                PakAssetType.GfxObjMesh,
+                gfxId));
+    }
+
+    [Fact]
+    public void PreparedSource_DistinguishesMissingCrcAndSchemaCorruption()
+    {
+        const uint setupId = 0x0200_0001u;
+        string missingPath = NewPath();
+        using (var writer = new PakWriter(missingPath, Header()))
+            writer.Finish();
+
+        using (var source = new PakPreparedAssetSource(
+                   missingPath,
+                   Identity))
+        {
+            Assert.Equal(
+                PreparedAssetReadStatus.Missing,
+                source.ReadSetupCollision(setupId).Status);
+        }
+
+        string schemaPath = NewPath();
+        byte[] malformed =
+            [.. FlatCollisionAssetSerializer.Serialize(SetupAsset()), 0x7F];
+        using (var writer = new PakWriter(schemaPath, Header()))
+        {
+            writer.AddBlob(
+                PakKey.Compose(PakAssetType.SetupCollision, setupId),
+                malformed);
+            writer.Finish();
+        }
+
+        using (var source = new PakPreparedAssetSource(schemaPath, Identity))
+        {
+            Assert.Equal(
+                PreparedAssetReadStatus.Corrupt,
+                source.ReadSetupCollision(setupId).Status);
+            Assert.Equal(
+                PreparedAssetPresence.Corrupt,
+                source.ProbeCollision(
+                    PakAssetType.SetupCollision,
+                    setupId));
+            Assert.Equal(
+                PreparedAssetReadStatus.Corrupt,
+                source.ReadSetupCollision(setupId).Status);
+        }
+
+        string crcPath = NewPath();
+        using (var writer = new PakWriter(crcPath, Header()))
+        {
+            writer.AddBlob(
+                PakKey.Compose(PakAssetType.SetupCollision, setupId),
+                FlatCollisionAssetSerializer.Serialize(SetupAsset()));
+            writer.Finish();
+        }
+        FlipFirstBlobByte(crcPath);
+        using var corruptSource =
+            new PakPreparedAssetSource(crcPath, Identity);
+        Assert.Equal(
+            PreparedAssetReadStatus.Corrupt,
+            corruptSource.ReadSetupCollision(setupId).Status);
+    }
+
+    [Fact]
+    public void PreparedSource_ConcurrentReadsRemainIndependentAndComplete()
+    {
+        const uint setupId = 0x0200_0001u;
+        string path = NewPath();
+        using (var writer = new PakWriter(path, Header()))
+        {
+            writer.AddBlob(
+                PakKey.Compose(PakAssetType.SetupCollision, setupId),
+                FlatCollisionAssetSerializer.Serialize(SetupAsset()));
+            writer.Finish();
+        }
+
+        using var source = new PakPreparedAssetSource(path, Identity);
+        Parallel.For(
+            0,
+            64,
+            _ =>
+            {
+                PreparedCollisionReadResult<FlatSetupCollision> result =
+                    source.ReadSetupCollision(setupId);
+                Assert.Equal(PreparedAssetReadStatus.Loaded, result.Status);
+                Assert.NotNull(result.Data);
+            });
+
+        Assert.Equal(64, source.CollisionStats.Reads);
+        Assert.Equal(64, source.CollisionStats.Loaded);
+        Assert.Equal(0, source.CollisionStats.Corrupt);
+    }
+
+    [Fact]
+    public void RenderDecoder_CannotPoisonCollisionTypedEntry()
+    {
+        const uint setupId = 0x0200_0001u;
+        string path = NewPath();
+        ulong key = PakKey.Compose(
+            PakAssetType.SetupCollision,
+            setupId);
+        using (var writer = new PakWriter(path, Header()))
+        {
+            writer.AddBlob(
+                key,
+                FlatCollisionAssetSerializer.Serialize(SetupAsset()));
+            writer.Finish();
+        }
+
+        using (var reader = new PakReader(path))
+        {
+            Assert.Equal(
+                PakObjectReadStatus.Missing,
+                reader.ReadObjectMeshData(key, out ObjectMeshData? mesh));
+            Assert.Null(mesh);
+            Assert.Equal(PakEntryState.Available, reader.ProbeEntry(key));
+        }
+
+        using var source = new PakPreparedAssetSource(path, Identity);
+        Assert.Equal(
+            PreparedAssetReadStatus.Loaded,
+            source.ReadSetupCollision(setupId).Status);
+    }
+
+    private static FlatGfxObjCollisionAsset GfxAsset() =>
+        new(
+            PhysicsBsp(),
+            new FlatCollisionSphere(
+                new Vector3(Float(0x3F80_0001), -0f, 3f),
+                Float(0x7FC0_1234)),
+            new FlatGfxObjVisualBounds(
+                new Vector3(-1, -2, -3),
+                new Vector3(4, 5, 6),
+                new Vector3(1.5f),
+                Float(0x4123_4567),
+                new Vector3(2.5f, 3.5f, 4.5f)));
+
+    private static FlatSetupCollision SetupAsset() =>
+        new(
+            ImmutableArray.Create(
+                new FlatCollisionCylinder(
+                    new Vector3(1, 2, 3),
+                    Float(0x3F00_0001),
+                    Float(0x4000_0001))),
+            ImmutableArray.Create(
+                new FlatCollisionSphere(
+                    new Vector3(-1, -2, -3),
+                    Float(0x4040_0001))),
+            Float(0x4080_0001),
+            Float(0x40A0_0001),
+            Float(0x40C0_0001),
+            Float(0x40E0_0001));
+
+    private static FlatCellStructureCollisionAsset CellStructureAsset() =>
+        new(
+            PhysicsBsp(),
+            new FlatCellContainmentBsp(
+                0,
+                ImmutableArray.Create(
+                    new FlatCellBspNode(
+                        BSPNodeType.BPIN,
+                        new Plane(Vector3.UnitX, -1),
+                        1,
+                        2,
+                        0),
+                    new FlatCellBspNode(
+                        BSPNodeType.Leaf,
+                        new Plane(Vector3.UnitY, -2),
+                        -1,
+                        -1,
+                        1),
+                    new FlatCellBspNode(
+                        BSPNodeType.Leaf,
+                        new Plane(Vector3.UnitZ, -3),
+                        -1,
+                        -1,
+                        2))),
+            PolygonTable());
+
+    private static FlatEnvCellTopology TopologyAsset() =>
+        new(
+            ImmutableArray.Create(
+                new FlatEnvCellPortal(0x0102, 3, 4, 0),
+                new FlatEnvCellPortal(0x0103, 8, 2, 1)),
+            ImmutableArray.Create(0xA9B4_0101u, 0xA9B4_0102u),
+            true);
+
+    private static FlatPhysicsBsp PhysicsBsp() =>
+        new(
+            0,
+            ImmutableArray.Create(
+                Node(BSPNodeType.BPIN, 1, 2, 0, 0, 0),
+                Node(BSPNodeType.Leaf, -1, -1, 1, 0, 1),
+                Node(BSPNodeType.Leaf, -1, -1, 2, 1, 1)),
+            ImmutableArray.Create(0, 1),
+            PolygonTable());
+
+    private static FlatPhysicsBspNode Node(
+        BSPNodeType type,
+        int positive,
+        int negative,
+        int leaf,
+        int polygonStart,
+        int polygonCount) =>
+        new(
+            type,
+            new Plane(
+                new Vector3(1 + leaf, 2 + leaf, 3 + leaf),
+                Float(0x3F80_0000u + (uint)leaf)),
+            positive,
+            negative,
+            leaf,
+            leaf & 1,
+            new FlatCollisionSphere(
+                new Vector3(4 + leaf, 5 + leaf, 6 + leaf),
+                7 + leaf),
+            new FlatIndexRange(polygonStart, polygonCount));
+
+    private static FlatPolygonTable PolygonTable() =>
+        new(
+            ImmutableArray.Create(
+                new FlatCollisionPolygon(
+                    3,
+                    new Plane(Vector3.UnitX, -1),
+                    CullMode.Clockwise,
+                    3,
+                    new FlatIndexRange(0, 3)),
+                new FlatCollisionPolygon(
+                    8,
+                    new Plane(Vector3.UnitY, -2),
+                    CullMode.CounterClockwise,
+                    3,
+                    new FlatIndexRange(3, 3))),
+            ImmutableArray.Create(
+                Vector3.Zero,
+                Vector3.UnitY,
+                Vector3.UnitZ,
+                Vector3.One,
+                Vector3.UnitX,
+                Vector3.UnitZ));
+
+    private string NewPath()
+    {
+        string path = Path.Combine(
+            Path.GetTempPath(),
+            $"acdream-flat-collision-{Guid.NewGuid():N}.pak");
+        _paths.Add(path);
+        return path;
+    }
+
+    private static PakHeader Header() =>
+        new()
+        {
+            PortalIteration = Identity.PortalIteration,
+            CellIteration = Identity.CellIteration,
+            HighResIteration = Identity.HighResIteration,
+            LanguageIteration = Identity.LanguageIteration,
+            BakeToolVersion = Identity.BakeToolVersion,
+        };
+
+    private static void FlipFirstBlobByte(string path)
+    {
+        using var stream = new FileStream(
+            path,
+            FileMode.Open,
+            FileAccess.ReadWrite,
+            FileShare.None);
+        stream.Position = PakHeader.Size + 4;
+        int value = stream.ReadByte();
+        Assert.NotEqual(-1, value);
+        stream.Position = PakHeader.Size + 4;
+        stream.WriteByte((byte)(value ^ 0xFF));
+    }
+
+    private static float Float(uint bits) =>
+        BitConverter.Int32BitsToSingle(unchecked((int)bits));
+
+    private static void AssertFloatBits(float expected, float actual) =>
+        Assert.Equal(
+            BitConverter.SingleToInt32Bits(expected),
+            BitConverter.SingleToInt32Bits(actual));
+
+    public void Dispose()
+    {
+        foreach (string path in _paths)
+        {
+            try
+            {
+                File.Delete(path);
+            }
+            catch
+            {
+                // Best-effort cleanup.
+            }
+        }
+    }
+}
diff --git a/tests/AcDream.Content.Tests/InstalledPreparedCollisionCatalogTests.cs b/tests/AcDream.Content.Tests/InstalledPreparedCollisionCatalogTests.cs
new file mode 100644
index 00000000..04bff25c
--- /dev/null
+++ b/tests/AcDream.Content.Tests/InstalledPreparedCollisionCatalogTests.cs
@@ -0,0 +1,58 @@
+using AcDream.Content.Pak;
+using DatReaderWriter;
+using DatReaderWriter.Options;
+
+namespace AcDream.Content.Tests;
+
+public sealed class InstalledPreparedCollisionCatalogTests
+{
+    [Fact]
+    public void InstalledPackage_ContainsAndReadsCanonicalCollisionKeys()
+    {
+        string? datDir = ResolveDatDir();
+        if (datDir is null)
+            return;
+
+        string packagePath = Path.Combine(datDir, "acdream.pak");
+        if (!File.Exists(packagePath))
+            return;
+
+        using var dats = new DatCollection(datDir, DatAccessType.Read);
+        using var adapter = new DatCollectionAdapter(dats);
+        using var source =
+            new PakPreparedAssetSource(packagePath, adapter);
+
+        Assert.Equal(
+            PreparedAssetReadStatus.Loaded,
+            source.ReadGfxObjCollision(0x0100_0A2Bu).Status);
+        Assert.Equal(
+            PreparedAssetReadStatus.Loaded,
+            source.ReadSetupCollision(0x0200_0001u).Status);
+        Assert.Equal(
+            PreparedAssetReadStatus.Loaded,
+            source.ReadCellStructureCollision(0xA9B4_013Fu).Status);
+        Assert.Equal(
+            PreparedAssetReadStatus.Loaded,
+            source.ReadEnvCellTopology(0xA9B4_013Fu).Status);
+        Assert.Equal(4, source.CollisionStats.Loaded);
+        Assert.True(source.MappedVirtualBytes > 1L << 30);
+    }
+
+    private static string? ResolveDatDir()
+    {
+        string? configured =
+            Environment.GetEnvironmentVariable("ACDREAM_DAT_DIR");
+        if (!string.IsNullOrWhiteSpace(configured)
+            && Directory.Exists(configured))
+        {
+            return configured;
+        }
+
+        string fallback = Path.Combine(
+            Environment.GetFolderPath(
+                Environment.SpecialFolder.UserProfile),
+            "Documents",
+            "Asheron's Call");
+        return Directory.Exists(fallback) ? fallback : null;
+    }
+}
diff --git a/tests/AcDream.Content.Tests/PakKeyTests.cs b/tests/AcDream.Content.Tests/PakKeyTests.cs
index ba527ac5..ce43efb9 100644
--- a/tests/AcDream.Content.Tests/PakKeyTests.cs
+++ b/tests/AcDream.Content.Tests/PakKeyTests.cs
@@ -35,6 +35,10 @@ public class PakKeyTests {
     [InlineData(PakAssetType.GfxObjMesh, 1)]
     [InlineData(PakAssetType.SetupMesh, 2)]
     [InlineData(PakAssetType.EnvCellMesh, 3)]
+    [InlineData(PakAssetType.GfxObjCollision, 4)]
+    [InlineData(PakAssetType.SetupCollision, 5)]
+    [InlineData(PakAssetType.CellStructureCollision, 6)]
+    [InlineData(PakAssetType.EnvCellTopology, 7)]
     public void AssetType_NumericValuesAreStable(PakAssetType type, byte expected) {
         // These values are a wire format — pin them so a future refactor can't
         // silently renumber the enum and corrupt existing paks.
diff --git a/tests/AcDream.Core.Tests/Physics/FlatCollisionInstalledDatTests.cs b/tests/AcDream.Core.Tests/Physics/FlatCollisionInstalledDatTests.cs
index 9783af7c..4f60b45e 100644
--- a/tests/AcDream.Core.Tests/Physics/FlatCollisionInstalledDatTests.cs
+++ b/tests/AcDream.Core.Tests/Physics/FlatCollisionInstalledDatTests.cs
@@ -43,6 +43,24 @@ public sealed class FlatCollisionInstalledDatTests
                 FlatCollisionAssetBuilder.FlattenCell(source);
             FlatCellCollisionAsset second =
                 FlatCollisionAssetBuilder.FlattenCell(source);
+            EnvCell datCell = Assert.IsType<EnvCell>(
+                dats.Get<EnvCell>(cellId));
+            var environment =
+                Assert.IsType<DatReaderWriter.DBObjs.Environment>(
+                    dats.Get<DatReaderWriter.DBObjs.Environment>(
+                        0x0D00_0000u | datCell.EnvironmentId));
+            Assert.True(
+                environment.Cells.TryGetValue(
+                    datCell.CellStructure,
+                    out CellStruct? cellStruct));
+            Assert.NotNull(cellStruct);
+            FlatCellStructureCollisionAsset directStructure =
+                FlatCollisionAssetBuilder.FlattenCellStructure(cellStruct!);
+            FlatEnvCellTopology directTopology =
+                FlatCollisionAssetBuilder.FlattenEnvCellTopology(
+                    cellId,
+                    datCell,
+                    directStructure.PortalPolygons);
 
             AssertPhysicsSourceMatches(source.BSP?.Root, source.Resolved, first.Structure.PhysicsBsp);
             AssertContainmentSourceMatches(
@@ -60,6 +78,22 @@ public sealed class FlatCollisionInstalledDatTests
             Assert.Equal(
                 first.Topology.VisibleCellIds.AsEnumerable(),
                 second.Topology.VisibleCellIds.AsEnumerable());
+            FlatCollisionAssetBuilderTests.AssertFlatPhysicsEqual(
+                first.Structure.PhysicsBsp,
+                directStructure.PhysicsBsp);
+            Assert.Equal(
+                first.Structure.ContainmentBsp.Nodes.AsEnumerable(),
+                directStructure.ContainmentBsp.Nodes.AsEnumerable());
+            AssertPolygonTableEqual(
+                first.Structure.PortalPolygons,
+                directStructure.PortalPolygons);
+            Assert.Equal(
+                first.Topology.Portals.AsEnumerable(),
+                directTopology.Portals.AsEnumerable());
+            Assert.Equal(
+                first.Topology.VisibleCellIds.AsEnumerable(),
+                directTopology.VisibleCellIds.AsEnumerable());
+            Assert.Equal(first.Topology.SeenOutside, directTopology.SeenOutside);
 
             _output.WriteLine(
                 $"cell 0x{cellId:X8}: physicsNodes={first.Structure.PhysicsBsp.Nodes.Length}, " +
@@ -97,6 +131,8 @@ public sealed class FlatCollisionInstalledDatTests
                 FlatCollisionAssetBuilder.FlattenGfxObj(
                     source,
                     cache.GetVisualBounds(gfxObjId));
+            FlatGfxObjCollisionAsset direct =
+                FlatCollisionAssetBuilder.FlattenGfxObj(gfxObj);
 
             AssertPhysicsSourceMatches(
                 source.BSP.Root,
@@ -107,6 +143,15 @@ public sealed class FlatCollisionInstalledDatTests
             AssertVisualBoundsBits(
                 Assert.IsType<GfxObjVisualBounds>(cache.GetVisualBounds(gfxObjId)),
                 flat.VisualBounds!.Value);
+            FlatCollisionAssetBuilderTests.AssertFlatPhysicsEqual(
+                flat.PhysicsBsp,
+                direct.PhysicsBsp);
+            AssertFlatNullableSphereBits(
+                flat.BoundingSphere,
+                direct.BoundingSphere);
+            AssertFlatNullableVisualBoundsBits(
+                flat.VisualBounds,
+                direct.VisualBounds);
 
             _output.WriteLine(
                 $"gfx 0x{gfxObjId:X8}: nodes={flat.PhysicsBsp.Nodes.Length}, " +
@@ -127,7 +172,10 @@ public sealed class FlatCollisionInstalledDatTests
 
             FlatSetupCollision flat =
                 FlatCollisionAssetBuilder.FlattenSetup(source);
+            FlatSetupCollision direct =
+                FlatCollisionAssetBuilder.FlattenSetup(setup);
             AssertSetupSourceMatches(source, flat);
+            AssertSetupFlatEqual(flat, direct);
 
             _output.WriteLine(
                 $"setup 0x{setupId:X8}: cylinders={flat.Cylinders.Length}, " +
@@ -327,4 +375,114 @@ public sealed class FlatCollisionInstalledDatTests
             source.HalfExtents,
             flat.HalfExtents);
     }
+
+    private static void AssertFlatNullableSphereBits(
+        FlatCollisionSphere? expected,
+        FlatCollisionSphere? actual)
+    {
+        Assert.Equal(expected.HasValue, actual.HasValue);
+        if (!expected.HasValue || !actual.HasValue)
+            return;
+        FlatCollisionAssetBuilderTests.AssertVectorBits(
+            expected.Value.Origin,
+            actual.Value.Origin);
+        FlatCollisionAssetBuilderTests.AssertFloatBits(
+            expected.Value.Radius,
+            actual.Value.Radius);
+    }
+
+    private static void AssertFlatNullableVisualBoundsBits(
+        FlatGfxObjVisualBounds? expected,
+        FlatGfxObjVisualBounds? actual)
+    {
+        Assert.Equal(expected.HasValue, actual.HasValue);
+        if (!expected.HasValue || !actual.HasValue)
+            return;
+        FlatCollisionAssetBuilderTests.AssertVectorBits(
+            expected.Value.Min,
+            actual.Value.Min);
+        FlatCollisionAssetBuilderTests.AssertVectorBits(
+            expected.Value.Max,
+            actual.Value.Max);
+        FlatCollisionAssetBuilderTests.AssertVectorBits(
+            expected.Value.Center,
+            actual.Value.Center);
+        FlatCollisionAssetBuilderTests.AssertFloatBits(
+            expected.Value.Radius,
+            actual.Value.Radius);
+        FlatCollisionAssetBuilderTests.AssertVectorBits(
+            expected.Value.HalfExtents,
+            actual.Value.HalfExtents);
+    }
+
+    private static void AssertSetupFlatEqual(
+        FlatSetupCollision expected,
+        FlatSetupCollision actual)
+    {
+        Assert.Equal(expected.Cylinders.Length, actual.Cylinders.Length);
+        Assert.Equal(expected.Spheres.Length, actual.Spheres.Length);
+        for (int i = 0; i < expected.Cylinders.Length; i++)
+        {
+            FlatCollisionAssetBuilderTests.AssertVectorBits(
+                expected.Cylinders[i].Origin,
+                actual.Cylinders[i].Origin);
+            FlatCollisionAssetBuilderTests.AssertFloatBits(
+                expected.Cylinders[i].Radius,
+                actual.Cylinders[i].Radius);
+            FlatCollisionAssetBuilderTests.AssertFloatBits(
+                expected.Cylinders[i].Height,
+                actual.Cylinders[i].Height);
+        }
+        for (int i = 0; i < expected.Spheres.Length; i++)
+        {
+            FlatCollisionAssetBuilderTests.AssertVectorBits(
+                expected.Spheres[i].Origin,
+                actual.Spheres[i].Origin);
+            FlatCollisionAssetBuilderTests.AssertFloatBits(
+                expected.Spheres[i].Radius,
+                actual.Spheres[i].Radius);
+        }
+        FlatCollisionAssetBuilderTests.AssertFloatBits(
+            expected.Height,
+            actual.Height);
+        FlatCollisionAssetBuilderTests.AssertFloatBits(
+            expected.Radius,
+            actual.Radius);
+        FlatCollisionAssetBuilderTests.AssertFloatBits(
+            expected.StepUpHeight,
+            actual.StepUpHeight);
+        FlatCollisionAssetBuilderTests.AssertFloatBits(
+            expected.StepDownHeight,
+            actual.StepDownHeight);
+    }
+
+    private static void AssertPolygonTableEqual(
+        FlatPolygonTable expected,
+        FlatPolygonTable actual)
+    {
+        Assert.Equal(expected.Polygons.Length, actual.Polygons.Length);
+        Assert.Equal(expected.Vertices.Length, actual.Vertices.Length);
+        for (int i = 0; i < expected.Polygons.Length; i++)
+        {
+            Assert.Equal(expected.Polygons[i].Id, actual.Polygons[i].Id);
+            Assert.Equal(
+                expected.Polygons[i].SidesType,
+                actual.Polygons[i].SidesType);
+            Assert.Equal(
+                expected.Polygons[i].NumPoints,
+                actual.Polygons[i].NumPoints);
+            Assert.Equal(
+                expected.Polygons[i].VertexRange,
+                actual.Polygons[i].VertexRange);
+            FlatCollisionAssetBuilderTests.AssertPlaneBits(
+                expected.Polygons[i].Plane,
+                actual.Polygons[i].Plane);
+        }
+        for (int i = 0; i < expected.Vertices.Length; i++)
+        {
+            FlatCollisionAssetBuilderTests.AssertVectorBits(
+                expected.Vertices[i],
+                actual.Vertices[i]);
+        }
+    }
 }