# Cylinder fallback dedupe (Phase A1) — 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:** Skip the mesh-AABB-fallback cylinder registration for
landblock stabs (`entity.Id & 0xFF000000u == 0xC0000000u`). Eliminates
"thin air" collisions inside cottages and around building exteriors.

**Architecture:** One-line bool definition near existing
`_isOutdoorMesh` declaration + one additional clause in the existing
`if` gate at the fallback's entry. No new files, no math changes, no
new tests beyond visual verification.

**Tech Stack:** C# .NET 10. Single source-file change.

**Spec:** [`docs/superpowers/specs/2026-05-21-cylinder-fallback-dedup-design.md`](../specs/2026-05-21-cylinder-fallback-dedup-design.md)

---

## File Structure

| File | Action | Responsibility |
|---|---|---|
| `src/AcDream.App/Rendering/GameWindow.cs` | Modify | Add `_isLandblockStab` flag + AND it into the mesh-AABB-fallback gate. ~3 lines added. |

No new tests. The fix is verified by a live capture (no [entity-source]
mesh-aabb-fallback emissions for 0xC0xxxxxx entities) + visual
verification (no thin-air collisions inside cottages).

---

## Task 1: Gate mesh-AABB-fallback on "not a landblock stab"

**Files:**
- Modify: `src/AcDream.App/Rendering/GameWindow.cs`
  - **Insertion site 1:** immediately after the existing `_isOutdoorMesh` / `_isScenery` declarations at lines 5826-5829.
  - **Insertion site 2:** add a clause to the existing `if` at line 6050-6052 (the gate around the mesh-AABB-fallback path).

- [ ] **Step 1: Add `_isLandblockStab` flag near `_isOutdoorMesh`**

Find this code at lines 5825-5830 in `GameWindow.cs`:

```csharp
            uint _srcPrefix = entity.SourceGfxObjOrSetupId & 0xFF000000u;
            bool _isOutdoorMesh = ((entity.Id & 0x80000000u) != 0)  // scenery
                || ((entity.Id < 0x40000000u)                        // stab
                    && (_srcPrefix == 0x01000000u || _srcPrefix == 0x02000000u));
            bool _isScenery = _isOutdoorMesh;
            if (_isScenery) scTried++;
```

Insert a new line immediately after `bool _isScenery = _isOutdoorMesh;`
(but before the `if (_isScenery) scTried++;`), so the block becomes:

```csharp
            uint _srcPrefix = entity.SourceGfxObjOrSetupId & 0xFF000000u;
            bool _isOutdoorMesh = ((entity.Id & 0x80000000u) != 0)  // scenery
                || ((entity.Id < 0x40000000u)                        // stab
                    && (_srcPrefix == 0x01000000u || _srcPrefix == 0x02000000u));
            bool _isScenery = _isOutdoorMesh;
            // ISSUES #83 / Phase A1 (2026-05-21): landblock stabs
            // (LandBlockInfo.Objects + Buildings) use entity.Id with the
            // 0xC0XXYY00+n layout per LandblockLoader.cs:55. Their BSP
            // collision covers the whole structure; the mesh-AABB-fallback
            // path below is for canopy-only-BSP procedural scenery
            // (0x80XXYY00+n) and produces a redundant 1.5m-clamped
            // invisible disc at the stab's mesh origin — the user-reported
            // "thin air" collision inside cottages. Gate the fallback to
            // exclude stabs. Spec:
            // docs/superpowers/specs/2026-05-21-cylinder-fallback-dedup-design.md.
            bool _isLandblockStab = (entity.Id & 0xFF000000u) == 0xC0000000u;
            if (_isScenery) scTried++;
```

- [ ] **Step 2: AND `!_isLandblockStab` into the existing fallback gate**

Find this code at lines 6050-6052:

```csharp
            if (!isPhantomSetup
                && (_isOutdoorMesh || (entityBsp == 0 && entityCyl == 0))
                && entity.MeshRefs.Count > 0)
```

Modify it to:

```csharp
            if (!isPhantomSetup
                && !_isLandblockStab
                && (_isOutdoorMesh || (entityBsp == 0 && entityCyl == 0))
                && entity.MeshRefs.Count > 0)
```

(One new line, `&& !_isLandblockStab`, inserted as the second clause.)

- [ ] **Step 3: Build the project**

Run: `dotnet build`

Expected: PASS — no compile errors. No warnings other than the
pre-existing baseline.

- [ ] **Step 4: Run the full Core test suite**

Run: `dotnet test tests/AcDream.Core.Tests/AcDream.Core.Tests.csproj`

Expected: PASS — same 8 pre-existing failures as baseline, no new
failures, no new passes.

- [ ] **Step 5: Commit**

```bash
git add src/AcDream.App/Rendering/GameWindow.cs
git commit -m "$(cat <<'EOF'
fix(physics): skip mesh-AABB-fallback cylinder for landblock stabs

ISSUES #83 Phase A1. Landblock stabs (entity.Id 0xC0XXYY00+n per
LandblockLoader.cs:55) were being registered with TWO collision
shadows: the correct per-part BSP at `entity.Id*256 + partIdx`, AND a
redundant mesh-AABB-fallback cylinder at `entity.Id`. The fallback
clamped to 1.5m radius, centered at the building's mesh origin,
producing user-reported "thin air" collisions inside cottages and
within 2m of building exteriors.

The fallback was originally designed for canopy-only-BSP procedural
scenery (0x80XXYY00+n) — trees whose BSP covers the canopy but not
the trunk. Landblock stabs have full BSP coverage and don't need it.

Probe evidence (launch-thinair capture):
- 0xC0A9B479 cylinder fallback (Holtburg cottage): 104 hits in a
  short capture session, all inside the cottage main room
  (cell=0xA9B4013F), ~2m from the building's mesh origin.
- 0xA9B47900 BSP (the actual cottage walls): 52 legitimate hits.

Fix: one new bool _isLandblockStab + one clause in the existing
mesh-AABB-fallback gate.

Spec: docs/superpowers/specs/2026-05-21-cylinder-fallback-dedup-design.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
EOF
)"
```

---

## Verification (manual, post-commit)

After the commit lands, re-run the thin-air capture:

```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_BUILDING       = "1"
$env:ACDREAM_PROBE_RESOLVE        = "1"
dotnet build -c Debug
dotnet run --project src\AcDream.App\AcDream.App.csproj --no-build -c Debug 2>&1 |
    Tee-Object -FilePath "launch-a1-verify.log"
```

User walks inside a Holtburg cottage and around outside. Expected:

1. **Visual:** can walk freely inside the cottage room — no invisible
   wall in the middle of the room.
2. **Log:** convert to UTF-8 and check:

```powershell
Get-Content launch-a1-verify.log -Encoding Unicode |
    Out-File launch-a1-verify.utf8.log -Encoding utf8
Get-Content launch-a1-verify.utf8.log |
    Where-Object { $_ -match '\[entity-source\].*note=mesh-aabb-fallback.*entityId=0xC0' } |
    Measure-Object | Select-Object -ExpandProperty Count
```

Expected: **0** (no 0xC0 entities now register a mesh-AABB-fallback).

Also expected: no `[resolve]` hits attribute to `0xC0XXYY79`-style
cylinder IDs.

---

## Self-review checklist

- [x] **Spec coverage**: spec components 1+2 (the bool + the gate clause) both implemented in Task 1 steps 1+2.
- [x] **No placeholders**: every step has the exact line numbers and code blocks.
- [x] **Type consistency**: `_isLandblockStab` is `bool`, referenced in the gate as `!_isLandblockStab`. Consistent.
- [x] **Atomic commit**: one commit, ~3 lines added, single file.
- [x] **Acceptance**: visual verification (no thin-air collision) + grep verification (no 0xC0 fallback registrations).
- [x] **No new tests**: justified — the fix is in `GameWindow.cs` (app layer), which doesn't have natural unit tests, and the behavior is verified by live capture per the spec.