docs(plan): indoor BSP world-origin fix implementation plan

Five-task plan for Bug B slice (spec 2026-05-20). Tasks: 1. Regression test in BSPQueryTests.cs (BSPQuery API contract) 2. Apply Decompose + arg-pass at TransitionTypes.cs:1442 3. Run physics suite, confirm 8-failure baseline holds 4. Commit 5. User visual + probe-equivalence verification Bug A explicitly deferred to a future slice. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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+# Indoor BSP World-Origin Fix Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Stop indoor BSP step-down + Path-4 land from writing local-space `ContactPlane`s by passing the cell's actual world rotation + world origin to `BSPQuery.FindCollisions`.
+
+**Architecture:** Single-call-site mechanical fix at `TransitionTypes.cs:1442`. Decompose `cellPhysics.WorldTransform` once, pass the rotation as `localToWorld` and the translation as `worldOrigin`. Mirrors the existing correct pattern at `:1808` for object BSP queries.
+
+**Tech Stack:** C# .NET 10, xUnit, `System.Numerics.Matrix4x4.Decompose`, existing `BSPQuery` / `Transition` / `CellPhysics` types.
+
+**Spec:** [`docs/superpowers/specs/2026-05-20-indoor-bsp-worldorigin-fix-design.md`](../specs/2026-05-20-indoor-bsp-worldorigin-fix-design.md)
+
+---
+
+## File Structure
+
+**Files to modify:**
+
+- `src/AcDream.Core/Physics/TransitionTypes.cs` — Single call site at `:1442`. Add 8-10 lines for `Matrix4x4.Decompose` + updated arg list.
+
+**Files to extend:**
+
+- `tests/AcDream.Core.Tests/Physics/BSPQueryTests.cs` — Add one regression test (~50 lines including fixture builder) at the end of the file. Verifies `BSPQuery.FindCollisions` with `path.StepDown=true` + non-identity `localToWorld` + non-zero `worldOrigin` writes a world-space `ContactPlane`.
+
+**No files created.** No files deleted (Bug A's `TryFindIndoorWalkablePlane` removal is a separate slice — out of scope for this plan).
+
+---
+
+## Task 1: Add regression test — BSPQuery.FindCollisions Path 3 with translated cell
+
+This test verifies the BSPQuery API's correctness when called with non-identity world transforms — it documents the expected behavior and guards against future regressions in `BSPQuery`. It will already pass before the fix at `:1442` (because `BSPQuery` itself is correct when called correctly), but it locks in the contract.
+
+**Files:**
+- Modify: `tests/AcDream.Core.Tests/Physics/BSPQueryTests.cs` — append a new test method after the existing `FindWalkableSphere_SteepPoly_RejectedByWalkableAllowance` test (the last one in the file, around line 421).
+
+- [ ] **Step 1: Write the failing test**
+
+Append to `tests/AcDream.Core.Tests/Physics/BSPQueryTests.cs` (after the last test method, before the closing `}` of the class):
+
+```csharp
+    // =========================================================================
+    // FindCollisions — world-origin / world-rotation correctness (spec 2026-05-20)
+    // =========================================================================
+
+    /// <summary>
+    /// Build a single-leaf BSP with one horizontal floor polygon at the given
+    /// cell-local Z. Vertex array forms a 4x4 m square centered at cell-local
+    /// (0, 0).
+    /// </summary>
+    private static (PhysicsBSPNode root, Dictionary<ushort, ResolvedPolygon> resolved)
+        BuildSingleFloorBsp(float floorZ)
+    {
+        var verts = new[]
+        {
+            new Vector3(-2f, -2f, floorZ),
+            new Vector3( 2f, -2f, floorZ),
+            new Vector3( 2f,  2f, floorZ),
+            new Vector3(-2f,  2f, floorZ),
+        };
+
+        var root = new PhysicsBSPNode
+        {
+            Type = BSPNodeType.Leaf,
+            BoundingSphere = new Sphere
+            {
+                Origin = new Vector3(0f, 0f, floorZ),
+                Radius = 3f,
+            },
+        };
+        root.Polygons.Add(0);
+
+        var resolved = new Dictionary<ushort, ResolvedPolygon>
+        {
+            [0] = new ResolvedPolygon
+            {
+                Vertices  = verts,
+                Plane     = new Plane(Vector3.UnitZ, -floorZ),
+                NumPoints = 4,
+                SidesType = CullMode.None,
+            },
+        };
+
+        return (root, resolved);
+    }
+
+    [Fact]
+    public void FindCollisions_StepDown_TranslatedWorldOrigin_WritesWorldSpacePlane()
+    {
+        // Cell is translated +94 m in world Z (i.e., the cell-local floor at
+        // Z=0 sits at world Z=94). This mirrors the Holtburg cottage scenario
+        // captured in launch-cp-probe.log (cell 0xA9B40150, floor world
+        // Z≈94.02).
+        var (root, resolved) = BuildSingleFloorBsp(floorZ: 0f);
+
+        var transition = new Transition();
+        transition.SpherePath.WalkableAllowance = PhysicsGlobals.FloorZ;
+        transition.SpherePath.WalkInterp        = 1.0f;
+        transition.SpherePath.StepDown          = true;
+        transition.SpherePath.StepDownAmt       = 0.5f;
+
+        // Foot sphere in cell-local space: just above the floor.
+        var localSphere = new Sphere
+        {
+            Origin = new Vector3(0f, 0f, 0.48f),
+            Radius = 0.48f,
+        };
+
+        var state = BSPQuery.FindCollisions(
+            root,
+            resolved,
+            transition,
+            localSphere,
+            localSphere1: null,
+            localCurrCenter: localSphere.Origin,
+            localSpaceZ: Vector3.UnitZ,
+            scale: 1.0f,
+            localToWorld: Quaternion.Identity,
+            engine: null,
+            worldOrigin: new Vector3(0f, 0f, 94f));
+
+        // Path 3 step-down should fire and adjust the sphere onto the floor.
+        Assert.Equal(TransitionState.Adjusted, state);
+
+        // ContactPlane must be in world space: normal stays (0,0,1) since the
+        // cell rotation is identity; D = -world_floor_Z = -94.
+        Assert.True(transition.CollisionInfo.ContactPlaneValid);
+        Assert.Equal(1.0f, transition.CollisionInfo.ContactPlane.Normal.Z, precision: 3);
+        Assert.Equal(-94.0f, transition.CollisionInfo.ContactPlane.D, precision: 2);
+    }
+```
+
+- [ ] **Step 2: Run the test to verify it passes**
+
+Run:
+```powershell
+dotnet test tests/AcDream.Core.Tests/AcDream.Core.Tests.csproj -c Debug --nologo --filter "FullyQualifiedName~FindCollisions_StepDown_TranslatedWorldOrigin"
+```
+
+Expected:
+```
+Passed!  - Failed:     0, Passed:     1, Skipped:     0, Total:     1
+```
+
+If it fails, examine the assertion output. The most likely failure mode: `TransitionState.OK` instead of `Adjusted` — means the step-down didn't adjust onto the floor. Adjust `StepDownAmt` / sphere position to ensure the sphere center is within `radius` of the floor plane so `find_walkable` accepts the contact.
+
+- [ ] **Step 3: Commit**
+
+```powershell
+git add tests/AcDream.Core.Tests/Physics/BSPQueryTests.cs
+git commit -m "test(physics): BSPQuery.FindCollisions writes world-space plane with translated origin
+
+Regression test for indoor BSP world-origin fix (Bug B). Verifies that
+BSPQuery.FindCollisions with path.StepDown=true and a non-zero
+worldOrigin parameter writes a world-space ContactPlane to
+CollisionInfo (not a cell-local-space one).
+
+Passes before the call-site fix at TransitionTypes.cs:1442 because
+BSPQuery itself is correct when called with the right args — it's the
+caller that was passing the defaults. This test locks in the BSPQuery
+contract so the relationship between worldOrigin/localToWorld input and
+ContactPlane.D output cannot regress silently.
+
+Spec: docs/superpowers/specs/2026-05-20-indoor-bsp-worldorigin-fix-design.md.
+
+Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>"
+```
+
+---
+
+## Task 2: Apply the call-site fix
+
+Decompose `cellPhysics.WorldTransform` and pass the rotation + translation to `BSPQuery.FindCollisions`. This is the actual bug fix.
+
+**Files:**
+- Modify: `src/AcDream.Core/Physics/TransitionTypes.cs:1442` — the BSP collision call inside the indoor branch of `FindEnvCollisions`. Replace the 10-arg invocation with a Decompose + 11-arg invocation including `localToWorld` + `worldOrigin`.
+
+- [ ] **Step 1: Read the current call site for exact context match**
+
+Read `src/AcDream.Core/Physics/TransitionTypes.cs` lines 1430-1455 to confirm the exact whitespace and surrounding code. (We need the exact `old_string` for the Edit tool.)
+
+- [ ] **Step 2: Apply the edit**
+
+Use Edit on `src/AcDream.Core/Physics/TransitionTypes.cs`:
+
+`old_string`:
+```csharp
+                // Use the full 6-path BSP dispatcher for retail-faithful collision.
+                // Use pre-resolved polygons (vertices+planes computed at cache time).
+                var cellState = BSPQuery.FindCollisions(
+                    cellPhysics.BSP.Root,
+                    cellPhysics.Resolved,
+                    this,
+                    localSphere,
+                    localSphere1,
+                    localCurrCenter,
+                    Vector3.UnitZ,  // local space Z is up
+                    1.0f,           // scale = 1.0 for cell geometry
+                    Quaternion.Identity,
+                    engine);        // engine needed for Path 5 step-up
+```
+
+`new_string`:
+```csharp
+                // Use the full 6-path BSP dispatcher for retail-faithful collision.
+                // Use pre-resolved polygons (vertices+planes computed at cache time).
+                //
+                // 2026-05-20 (Bug B fix): pass the cell's world rotation +
+                // translation so the BSP's internal find_walkable /
+                // step_sphere_down / Path-4 land write world-space ContactPlanes
+                // (NOT cell-local). The prior call passed Quaternion.Identity
+                // and defaulted worldOrigin = Vector3.Zero — which corrupted
+                // every Path 3 + Path 4 CP write inside an indoor cell with
+                // D ≈ 0 instead of D = -world_floor_Z. Mirrors the existing
+                // correct pattern at the FindObjCollisions call site.
+                //
+                // Retail oracle: BSPTREE::find_collisions (decomp
+                // acclient_2013_pseudo_c.txt:323924) calls Plane::localtoglobal
+                // (:323921) before set_contact_plane. Our TransformNormal +
+                // TransformVertices + BuildWorldPlane chain is the equivalent
+                // — it just needs the right rotation + origin.
+                Quaternion cellRotation;
+                Vector3    cellOrigin;
+                if (Matrix4x4.Decompose(cellPhysics.WorldTransform, out _, out cellRotation, out cellOrigin))
+                {
+                    // Clean decompose — use the extracted rotation + translation.
+                }
+                else
+                {
+                    // Matrix has shear or other non-decomposable parts. EnvCell
+                    // WorldTransform is always rigid rotation + translation per
+                    // the dat format, so this branch should never fire. Log a
+                    // one-shot warning + fall back to identity rotation +
+                    // .Translation so we degrade to "translation-only" instead
+                    // of the original "both broken".
+                    Console.WriteLine(System.FormattableString.Invariant(
+                        $"[indoor-bsp] WARN cellPhysics.WorldTransform did not decompose cleanly for cell 0x{sp.CheckCellId:X8} — falling back to identity rotation"));
+                    cellRotation = Quaternion.Identity;
+                    cellOrigin   = cellPhysics.WorldTransform.Translation;
+                }
+
+                var cellState = BSPQuery.FindCollisions(
+                    cellPhysics.BSP.Root,
+                    cellPhysics.Resolved,
+                    this,
+                    localSphere,
+                    localSphere1,
+                    localCurrCenter,
+                    Vector3.UnitZ,  // local space Z is up
+                    1.0f,           // scale = 1.0 for cell geometry
+                    cellRotation,
+                    engine,         // engine needed for Path 5 step-up
+                    worldOrigin: cellOrigin);
+```
+
+- [ ] **Step 3: Build to verify the change compiles**
+
+Run:
+```powershell
+dotnet build -c Debug
+```
+
+Expected: `Build succeeded.` with 0 errors. Warnings unchanged from baseline (3 pre-existing xUnit warnings).
+
+- [ ] **Step 4: Run the regression test (Task 1's) to verify it still passes**
+
+Run:
+```powershell
+dotnet test tests/AcDream.Core.Tests/AcDream.Core.Tests.csproj -c Debug --no-build --nologo --filter "FullyQualifiedName~FindCollisions_StepDown_TranslatedWorldOrigin"
+```
+
+Expected:
+```
+Passed!  - Failed:     0, Passed:     1, Skipped:     0, Total:     1
+```
+
+(The Task 1 test exercises `BSPQuery` directly; this fix is at the caller, so the test still passes.)
+
+---
+
+## Task 3: Run the broader physics test suite — confirm no regressions
+
+Verify the existing 8-failure baseline is unchanged (2 BSPStepUp + 6 MotionInterpreter pre-existing failures, all unrelated to this fix).
+
+- [ ] **Step 1: Run all physics tests**
+
+Run:
+```powershell
+dotnet test tests/AcDream.Core.Tests/AcDream.Core.Tests.csproj -c Debug --no-build --nologo --filter "FullyQualifiedName~Physics"
+```
+
+Expected:
+```
+Failed!  - Failed:     8, Passed:   ...(at least 405), Skipped:     0, Total:   ...
+```
+
+The 8 failures are the documented baseline. If you see 9+ failures or different failure names, the fix introduced a regression — investigate before continuing.
+
+- [ ] **Step 2: Cross-check the failures match the baseline**
+
+Verify the failed test names match this set (no new failures, no new passes that were previously failing):
+
+Expected failing tests:
+```
+AcDream.Core.Tests.Physics.MotionInterpreterTests.GetMaxSpeed_WalkForward_ReturnsWalkAnimSpeed
+AcDream.Core.Tests.Physics.MotionInterpreterTests.GetMaxSpeed_Idle_ReturnsZero
+AcDream.Core.Tests.Physics.MotionInterpreterTests.GetMaxSpeed_WalkBackward_ReturnsWalkAnimSpeedTimesBackwardsFactor
+AcDream.Core.Tests.Physics.MotionInterpreterTests.GetMaxSpeed_*  (3 more)
+AcDream.Core.Tests.Physics.BSPStepUpTests.C3_Path6_AirborneMoverHitsSteepSlope_SetsCollide
+AcDream.Core.Tests.Physics.BSPStepUpTests.*  (1 more)
+```
+
+If the failing-test list has changed, stop and investigate. The fix should not affect motion-interpreter or step-up behavior.
+
+---
+
+## Task 4: Commit the fix
+
+- [ ] **Step 1: Stage the modified file**
+
+```powershell
+git add src/AcDream.Core/Physics/TransitionTypes.cs
+git status
+```
+
+Expected `git status`:
+```
+Changes to be committed:
+  modified:   src/AcDream.Core/Physics/TransitionTypes.cs
+```
+
+(Only `TransitionTypes.cs` should be staged. If the test file appears, it was already committed in Task 1.)
+
+- [ ] **Step 2: Commit with the spec's commit message**
+
+```powershell
+git commit -m "fix(physics): pass cell world-transform to indoor BSP collision
+
+Indoor cell BSP queries at TransitionTypes.cs:1442 were calling
+BSPQuery.FindCollisions with Quaternion.Identity + defaulted
+Vector3.Zero worldOrigin. Inside the BSP, Path 3 (step_sphere_down)
+and Path 4 (land-on-surface) use those params to build the
+world-space ContactPlane. Result: planes written with D ~ 0 instead
+of the cell's world floor Z (e.g. -94.02 for Holtburg cottages).
+320 corrupt CP writes per Holtburg session per the [cp-write] probe.
+
+Fix: decompose cellPhysics.WorldTransform once at the call site,
+pass the rotation as localToWorld and the translation as
+worldOrigin. Mirrors the existing correct pattern at :1808
+(FindObjCollisions, passes obj.Rotation + obj.Position).
+
+Retail oracle: BSPTREE::find_collisions (acclient_2013_pseudo_c.txt:323924)
+calls Plane::localtoglobal at :323921 before set_contact_plane.
+Our TransformNormal + TransformVertices + BuildWorldPlane chain is
+the equivalent — it just needs the right rotation + origin.
+
+Spec: docs/superpowers/specs/2026-05-20-indoor-bsp-worldorigin-fix-design.md.
+Evidence: launch-cp-probe.log capture 2026-05-20, [cp-write] probe.
+
+Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>"
+```
+
+- [ ] **Step 3: Verify commit landed cleanly**
+
+```powershell
+git log --oneline -3
+```
+
+Expected: top of log shows the fix commit, followed by the regression-test commit from Task 1, followed by `865634f docs(spec): indoor BSP world-origin / world-rotation fix (Bug B)`.
+
+---
+
+## Task 5: Hand off to user for visual verification
+
+The fix's acceptance test is visual + probe-equivalence. The user drives the client and confirms (a) `[cp-write] caller=BSPQuery.StepSphereDown:1123` lines now show correct world-Z D values, and (b) indoor walking visual scenarios behave better.
+
+- [ ] **Step 1: Confirm graceful-logout state**
+
+Before launching, check no stale acdream client is running (per CLAUDE.md's logout-before-reconnect rules). Run:
+```powershell
+Get-Process -Name AcDream.App -ErrorAction SilentlyContinue
+```
+
+If a process is listed, close it gracefully first:
+```powershell
+$proc = Get-Process -Name AcDream.App -ErrorAction SilentlyContinue
+if ($proc) {
+    $proc.CloseMainWindow() | Out-Null
+    $proc.WaitForExit(5000) | Out-Null
+}
+Start-Sleep -Seconds 3
+```
+
+- [ ] **Step 2: Tell the user the launch command**
+
+Show the user (do NOT auto-launch — user retains control here):
+
+> Fix landed. Ready for visual verification. Launch with the probe flags on:
+>
+> ```powershell
+> $env:ACDREAM_DAT_DIR   = "$env:USERPROFILE\Documents\Asheron's Call"
+> $env:ACDREAM_LIVE      = "1"
+> $env:ACDREAM_TEST_HOST = "127.0.0.1"
+> $env:ACDREAM_TEST_PORT = "9000"
+> $env:ACDREAM_TEST_USER = "testaccount"
+> $env:ACDREAM_TEST_PASS = "testpassword"
+> $env:ACDREAM_DEVTOOLS  = "1"
+> $env:ACDREAM_PROBE_INDOOR_BSP    = "1"
+> $env:ACDREAM_PROBE_CONTACT_PLANE = "1"
+> dotnet run --project src\AcDream.App\AcDream.App.csproj --no-build -c Debug 2>&1 | Tee-Object -FilePath "launch-cp-probe-postfix.log"
+> ```
+>
+> Walk these scenarios (~30 seconds each):
+> 1. **Cottage entry** (outdoor → indoor)
+> 2. **Indoor standstill** for ~10 seconds (stationary case — may still glitch; that's Bug A, expected)
+> 3. **2nd-floor walking** (primary success criterion for Bug B)
+> 4. **Cellar descent**
+> 5. **Single-floor cottage walk** (regression check)
+>
+> Then close the window (CloseMainWindow path for graceful logout). I'll grep the new log for the `StepSphereDown:1123` lines and confirm the D values are now correct.
+
+- [ ] **Step 3: Read + analyze the post-fix log**
+
+After the user closes the window, run:
+
+```powershell
+Get-Content launch-cp-probe-postfix.log -Encoding Unicode | Out-File launch-cp-probe-postfix.utf8.log -Encoding utf8
+```
+
+Then use Bash:
+```bash
+echo "=== StepSphereDown D distribution (post-fix) ==="
+grep -E 'caller=BSPQuery\.StepSphereDown' launch-cp-probe-postfix.utf8.log | grep -oE 'D=[-0-9.]+' | sort | uniq -c | sort -rn | head -10
+echo "=== Caller distribution (compare to pre-fix) ==="
+grep -oE 'caller=[A-Za-z_.:0-9]+' launch-cp-probe-postfix.utf8.log | sort | uniq -c | sort -rn | head -10
+echo "=== indoor-walkable result distribution (should be ~same; Bug A still active) ==="
+grep -oE '\[indoor-walkable\].*result=[A-Z]+' launch-cp-probe-postfix.utf8.log | grep -oE 'result=[A-Z]+' | sort | uniq -c
+```
+
+Expected:
+- StepSphereDown D values cluster around realistic floor Z values (-94.0, -94.02, etc., depending on the cell), NOT D=-0.000.
+- StepSphereDown caller count is similar to pre-fix (~320) OR much lower (the `Plane`-equality suppression in the property setter hides duplicate writes; if seed and BSP-write both produce the same world plane, only the seed shows up).
+- indoor-walkable MISS/HIT ratio still ~99% MISS (Bug A unchanged).
+
+- [ ] **Step 4: Hand off to the user with the assessment**
+
+Tell the user one of:
+
+**On success (D values now correct):**
+> Probe-equivalence verified — StepSphereDown D values are now world-Z (e.g. -94.02), not -0.000. Bug B closed. Visual report? If 2nd-floor walking is stabler but stationary cases (cellar entry, indoor standstill) still glitch, that's Bug A — next slice. If you saw the M2-critical indoor scenarios work end-to-end, we can decide whether to ship Bug A as a follow-up phase or punt to post-M2 polish.
+
+**On failure (D values still wrong):**
+> StepSphereDown D values are still wrong (showing X / -0.000 / etc.). The Decompose path either didn't fire or extracted the wrong values. Investigate: check what `cellPhysics.WorldTransform` actually looks like for the affected cells (might need a one-shot `[cell-transform]` probe).
+
+---
+
+## Self-review (run after writing this plan)
+
+- **Spec coverage:** Plan covers the spec's Fix section (Task 2), Verification section (Task 3 + Task 5), and the call-site change (Task 2). The risk R1 (cell scale) is acknowledged in-spec but no plan task — fine, deferred. Risk R2 (Decompose returns false) handled inline in Task 2's `else` branch. Risk R3 + R4 informational; no plan task needed.
+- **Placeholder scan:** No TBD/TODO. Every code block is complete. Commands have exact expected output strings.
+- **Type consistency:** `cellRotation` (Quaternion), `cellOrigin` (Vector3), `cellPhysics.WorldTransform` (Matrix4x4) — consistent across Task 2.
+- **Test coverage:** Task 1 covers BSPQuery API regression. Visual verification (Task 5) covers the call-site fix. Acceptable per project convention for one-line mechanical fixes with probe evidence.
+- **Bug A is explicitly out of scope.** Plan acknowledges it (Task 5 step 4) and defers to a future slice.