# Indoor Walkable-Plane Synthesis Removal 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:** Delete the per-frame `Transition.TryFindIndoorWalkablePlane` synthesis + outdoor-terrain fallthrough from the indoor branch of `FindEnvCollisions`, restoring retail's "ContactPlane retained on OK" behavior.

**Architecture:** Pure deletion. Replace the ~50-line synthesis block in `FindEnvCollisions` with `return TransitionState.OK;`. Delete the now-orphan helper method + constant + 2 test files (9 tests total). Net delta about -480 lines.

**Tech Stack:** C# .NET 10, xUnit, existing `BSPQuery` / `Transition` / `CellPhysics` types.

**Spec:** [`docs/superpowers/specs/2026-05-20-indoor-walkable-synthesis-removal-design.md`](../specs/2026-05-20-indoor-walkable-synthesis-removal-design.md)

**Predecessor:** [`docs/superpowers/specs/2026-05-20-indoor-bsp-worldorigin-fix-design.md`](../specs/2026-05-20-indoor-bsp-worldorigin-fix-design.md) (Bug B, shipped `de8ffde`).

---

## File Structure

**Files modified:**

- `src/AcDream.Core/Physics/TransitionTypes.cs` — three deletions in this one file:
  1. The synthesis block in `FindEnvCollisions` (about lines 1506-1558), replaced with `return TransitionState.OK;`.
  2. The `TryFindIndoorWalkablePlane` method itself (about lines 1269-1372, including doc-comment).
  3. The `INDOOR_WALKABLE_PROBE_DISTANCE` constant (about lines 1374-1381).

**Files deleted:**

- `tests/AcDream.Core.Tests/Physics/IndoorWalkablePlaneTests.cs` (291 lines, 8 tests).
- `tests/AcDream.Core.Tests/Physics/TransitionTypesTests.cs` (111 lines, 1 test).

**Files intentionally preserved:**

- `src/AcDream.Core/Physics/BSPQuery.cs` — `FindWalkableSphere` + `FindWalkableInternal`'s `hitPolyId` ref param stay.
- `tests/AcDream.Core.Tests/Physics/BSPQueryTests.cs` — all 5 `FindWalkableSphere_*` tests + the Bug B regression test stay.
- `src/AcDream.Core/Physics/PhysicsDiagnostics.cs` — `[cp-write]` probe stays.

---

## Task 1: Replace per-frame synthesis call site with `return OK`

The synthesis block sits inside the indoor branch of `FindEnvCollisions`, immediately after the `cellState != TransitionState.OK` early-return.

**Files:**
- Modify: `src/AcDream.Core/Physics/TransitionTypes.cs` (about lines 1506-1558).

- [ ] **Step 1: Read the lines to confirm exact whitespace**

Run Read on `src/AcDream.Core/Physics/TransitionTypes.cs` with offset=1498 and limit=65. Confirm the block from the `if (cellState != TransitionState.OK)` early-return through the trailing `}` closing the indoor BSP branch matches what the Edit will operate on.

- [ ] **Step 2: Apply the Edit to TransitionTypes.cs**

Use the Edit tool with the following parameters. The `old_string` is the existing synthesis block; the `new_string` is the bare `return TransitionState.OK;`.

OLD_STRING (paste into Edit's `old_string` exactly, including leading whitespace):

```
                if (cellState != TransitionState.OK)
                {
                    if (!ObjectInfo.State.HasFlag(ObjectInfoState.Contact))
                        ci.CollidedWithEnvironment = true;
                    return cellState;
                }

                // ── Synthesize indoor walkable contact plane ──────────────
                // Indoor walking Phase 2 follow-up (2026-05-19). When the BSP
                // returns OK (no wall collision), the player is standing on a
                // floor poly inside the cell. We must NOT fall through to
                // outdoor terrain (SampleTerrainWalkable) — the outdoor terrain
                // Z is below the indoor floor due to the +0.02f Z-bump applied
                // for render z-fight prevention. ValidateWalkable would then see
                // the player 0.5m above the outdoor plane → marks them as
                // airborne → walkable=False → falling animation, never recovers.
                //
                // Retail: CEnvCell::find_env_collisions returns from the cell
                // branch with the cell's walkable plane set — no fall-through
                // to terrain.
                bool walkableHit = TryFindIndoorWalkablePlane(
                    cellPhysics, localCenter, sphereRadius,
                    out var indoorPlane,
                    out var indoorVertices,
                    out uint hitPolyId);

                if (PhysicsDiagnostics.ProbeIndoorBspEnabled)
                {
                    if (walkableHit)
                    {
                        // dz = signed gap between foot and synthesized plane.
                        // Plane: N·p + D = 0  ⇒  pZ_on_plane = -D/N.z (for upward-facing planes)
                        // gap   = foot.Z - pZ_on_plane = foot.Z - (-D/N.z) = foot.Z + D/N.z
                        float dz = footCenter.Z + indoorPlane.D / indoorPlane.Normal.Z;
                        Console.WriteLine(System.FormattableString.Invariant(
                            $"[indoor-walkable] cell=0x{sp.CheckCellId:X8} wpos=({footCenter.X:F3},{footCenter.Y:F3},{footCenter.Z:F3}) probe={INDOOR_WALKABLE_PROBE_DISTANCE:F2} result=HIT poly=0x{hitPolyId:X4} wn=({indoorPlane.Normal.X:F3},{indoorPlane.Normal.Y:F3},{indoorPlane.Normal.Z:F3}) wD={indoorPlane.D:F3} dz={dz:+0.00;-0.00;+0.00}"));
                    }
                    else
                    {
                        Console.WriteLine(System.FormattableString.Invariant(
                            $"[indoor-walkable] cell=0x{sp.CheckCellId:X8} wpos=({footCenter.X:F3},{footCenter.Y:F3},{footCenter.Z:F3}) probe={INDOOR_WALKABLE_PROBE_DISTANCE:F2} result=MISS"));
                    }
                }

                if (walkableHit)
                {
                    return ValidateWalkable(
                        footCenter,
                        sphereRadius,
                        indoorPlane,
                        isWater: false,
                        waterDepth: 0f,
                        cellId: sp.CheckCellId,
                        walkableVertices: indoorVertices);
                }
                // If no walkable floor was found under the player indoors
                // (rare — cell with only walls/ceiling), fall through to
                // outdoor terrain as a defensive backstop. Indoor walking
                // will report walkable=False until the player moves over a
                // cell with a proper floor poly.
            }
        }
```

NEW_STRING (paste into Edit's `new_string`):

```
                if (cellState != TransitionState.OK)
                {
                    if (!ObjectInfo.State.HasFlag(ObjectInfoState.Contact))
                        ci.CollidedWithEnvironment = true;
                    return cellState;
                }

                // Indoor BSP returned OK — no wall collision. ContactPlane
                // is RETAINED from the prior tick's seed
                // (PhysicsEngine.ResolveWithTransition:583, the
                // init_contact_plane equivalent) OR refreshed by Path 3
                // step-down / Path 4 land if those fired this tick. Either
                // way, no synthesis is needed here — matches retail's
                // BSPTREE::find_collisions OK path
                // (acclient_2013_pseudo_c.txt:323938).
                //
                // Do NOT fall through to outdoor terrain backstop: the
                // player is in an indoor cell, and the outdoor terrain
                // Z is below the indoor floor by ~0.02m (the render Z-bump),
                // which would mark the player as airborne and trigger the
                // falling-animation stuck symptom (the original Bug A).
                // 2026-05-20 slice 2 of indoor ContactPlane retention.
                return TransitionState.OK;
            }
        }
```

- [ ] **Step 3: Build to verify the source still compiles**

Run:
```
dotnet build -c Debug 2>&1 | tail -5
```

Expected: `Build succeeded.` with 0 errors. (The `TryFindIndoorWalkablePlane` method is still defined; we haven't removed it yet. It just has no callers now, which is a warning at most.)

---

## Task 2: Delete the orphan `TryFindIndoorWalkablePlane` method + constant

After Task 1, `TryFindIndoorWalkablePlane` has no production callers. Tests in `IndoorWalkablePlaneTests.cs` and `TransitionTypesTests.cs` still reference it — they will be deleted in Task 3. For now, the build will go RED after this task and recover in Task 3.

**Files:**
- Modify: `src/AcDream.Core/Physics/TransitionTypes.cs` (about lines 1269-1381).

- [ ] **Step 1: Read the method + constant block**

Run Read on `src/AcDream.Core/Physics/TransitionTypes.cs` with offset=1268 and limit=115. Confirm the block from the `/// <summary>` doc-comment opening `TryFindIndoorWalkablePlane`, through the method body, through the `INDOOR_WALKABLE_PROBE_DISTANCE` constant + its doc-comment, ends at the blank line before the `/// <summary>` doc-comment for `FindEnvCollisions`.

- [ ] **Step 2: Apply the Edit**

Use the Edit tool. The `old_string` is the entire method + constant block (lines about 1269-1381). The `new_string` is empty (just a single blank line to keep the file structure clean between the `Fmt` helper above and the `Environment collision` section header).

OLD_STRING starts with this line:
```
    /// <summary>
    /// Synthesize the indoor walkable contact plane for the player's current
```

and ends with this line:
```
    private const float INDOOR_WALKABLE_PROBE_DISTANCE = 0.5f;
```

Read the file FIRST (Step 1 above) to capture the exact bytes between those two markers, then paste them as `old_string`.

NEW_STRING:
```
```

(empty — just delete the block entirely. The `// Environment collision — outdoor terrain` section header at about line 1265 sits directly above the deleted region; after deletion it will sit directly above the `FindEnvCollisions` doc-comment, which is the correct placement.)

- [ ] **Step 3: Build to confirm source-only orphaned helper is gone**

Run:
```
dotnet build -c Debug src/AcDream.Core/AcDream.Core.csproj 2>&1 | tail -5
```

Expected: `Build succeeded.` with 0 errors in `AcDream.Core.csproj`. (`AcDream.Core.Tests.csproj` will fail to build at this point — the test files still reference `TryFindIndoorWalkablePlane`. That's intentional; Task 3 fixes it.)

---

## Task 3: Delete the obsolete test files

The two test files in `tests/AcDream.Core.Tests/Physics/` exist solely to cover `Transition.TryFindIndoorWalkablePlane`. With the method deleted, the tests are dead code. Delete both files outright.

**Files:**
- Delete: `tests/AcDream.Core.Tests/Physics/IndoorWalkablePlaneTests.cs`
- Delete: `tests/AcDream.Core.Tests/Physics/TransitionTypesTests.cs`

- [ ] **Step 1: Confirm the file contents are TryFindIndoorWalkablePlane-only**

Run:
```
grep -c 'TryFindIndoorWalkablePlane' tests/AcDream.Core.Tests/Physics/IndoorWalkablePlaneTests.cs tests/AcDream.Core.Tests/Physics/TransitionTypesTests.cs
```

Expected: both files have non-zero matches (confirming they touch the deleted method). If either has 0 matches, STOP and investigate — that file is not what the spec assumed.

- [ ] **Step 2: Delete the files**

Run:
```
git rm tests/AcDream.Core.Tests/Physics/IndoorWalkablePlaneTests.cs tests/AcDream.Core.Tests/Physics/TransitionTypesTests.cs
```

Expected:
```
rm 'tests/AcDream.Core.Tests/Physics/IndoorWalkablePlaneTests.cs'
rm 'tests/AcDream.Core.Tests/Physics/TransitionTypesTests.cs'
```

- [ ] **Step 3: Build to confirm both projects compile**

Run:
```
dotnet build -c Debug 2>&1 | tail -5
```

Expected: `Build succeeded.` with 0 errors across all projects. If there's still a build failure pointing at `TryFindIndoorWalkablePlane`, search the codebase for any other reference:
```
grep -rn 'TryFindIndoorWalkablePlane' src tests
```

(should return 0 results after Tasks 1-3 are complete).

---

## Task 4: Run the physics test suite, confirm baseline holds

After deletion, the test count drops by 9 (the 9 deleted tests). The 6 pre-existing physics failures (3 MotionInterpreter + 2 BSPStepUp + 1 PositionManager) should still be the only failures.

- [ ] **Step 1: Run physics tests**

Run:
```
dotnet test tests/AcDream.Core.Tests/AcDream.Core.Tests.csproj -c Debug --no-build --nologo --filter "FullyQualifiedName~Physics"
```

Expected (the failing count should match the pre-existing baseline of 6):
```
Failed!  - Failed:     6, Passed:   ...(around 398-402), Skipped:     0, Total:   ...
```

If you see 7+ failures or any failure name NOT in this set, STOP and investigate:
```
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.BSPStepUpTests.C3_Path6_AirborneMoverHitsSteepSlope_SetsCollide
AcDream.Core.Tests.Physics.BSPStepUpTests.D4_AirborneMover_TallWall_PersistsSlidingNormalAcrossFrames
AcDream.Core.Tests.Physics.PositionManagerTests.ComputeOffset_BothActive_Combined
```

- [ ] **Step 2: Run the full Core test suite for good measure**

Run:
```
dotnet test tests/AcDream.Core.Tests/AcDream.Core.Tests.csproj -c Debug --no-build --nologo
```

Expected: 8 failed total (the 6 physics above + the 2 non-physics ones from the broader 1126-test suite). If the broader suite shows new failures, investigate.

---

## Task 5: Commit the change (single commit per spec)

The spec calls for a single commit covering the synthesis removal + method deletion + test deletion.

- [ ] **Step 1: Stage all changes**

Run:
```
git add src/AcDream.Core/Physics/TransitionTypes.cs
git add -u tests/AcDream.Core.Tests/Physics/IndoorWalkablePlaneTests.cs tests/AcDream.Core.Tests/Physics/TransitionTypesTests.cs
git status
```

Expected `git status`:
```
Changes to be committed:
  modified:   src/AcDream.Core/Physics/TransitionTypes.cs
  deleted:    tests/AcDream.Core.Tests/Physics/IndoorWalkablePlaneTests.cs
  deleted:    tests/AcDream.Core.Tests/Physics/TransitionTypesTests.cs
```

If the test files were removed via `git rm` in Task 3 they should already be staged; `git add -u` just ensures any straggler is captured.

- [ ] **Step 2: Commit with the spec's commit message**

Run:
```
git commit -m "fix(physics): remove per-frame indoor walkable-plane synthesis

The indoor branch of FindEnvCollisions called Transition.TryFindIndoorWalkablePlane
every frame to re-synthesize the ContactPlane after BSP returned OK.
The synthesis routed through BSPQuery.FindWalkableSphere -> walkable_hits_sphere,
which correctly rejects tangent contact via |dist| > radius - epsilon. For a
grounded player standing on or brushing a floor, the foot sphere is
tangent: 99.87% MISS rate per the 2026-05-20 [cp-write] probe.
Each MISS fell through to outdoor terrain backstop, writing a
ContactPlane that's below the indoor floor by ~0.02m, marking the
player airborne and triggering the falling-animation stuck symptom.

Fix: delete the synthesis + outdoor-fallthrough from the indoor OK
path. ContactPlane is retained from the prior tick's seed
(PhysicsEngine.ResolveWithTransition:583, init_contact_plane equivalent)
or refreshed by BSP Path 3 / Path 4 during the same tick. Matches
retail's BSPTREE::find_collisions OK path
(acclient_2013_pseudo_c.txt:323938).

Also deletes:
- Transition.TryFindIndoorWalkablePlane (~80 lines)
- INDOOR_WALKABLE_PROBE_DISTANCE constant
- [indoor-walkable] probe log line
- IndoorWalkablePlaneTests.cs (8 tests, the helper's coverage)
- TransitionTypesTests.cs (1 test, also tested the helper)

Net: ~-480 lines. BSPQuery.FindWalkableSphere + its 5 tests retained
as the underlying retail-faithful walkable-finder API.

Closes Bug A in the indoor ContactPlane retention phase.
Spec: docs/superpowers/specs/2026-05-20-indoor-walkable-synthesis-removal-design.md.
Predecessor: de8ffde (Bug B, BSP world-origin fix).

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

- [ ] **Step 3: Verify commit landed**

Run:
```
git log --oneline -7
```

Expected: top of log shows the new fix commit, followed by `3bec18f` (Bug A spec), `de8ffde` (Bug B fix), `39d4e65` (Bug B regression test), `56816fc` (Bug B plan), `865634f` (Bug B spec), `66de00d` ([cp-write] probe).

---

## Task 6: Hand off to user for visual verification

The fix's primary acceptance test is visual: the user walks the 5 scenarios with the probes enabled and reports whether the stuck-falling symptom is gone.

- [ ] **Step 1: Close any stale acdream client process**

Run:
```
$proc = Get-Process -Name AcDream.App -ErrorAction SilentlyContinue
if ($proc) {
    $proc.CloseMainWindow() | Out-Null
    $proc.WaitForExit(5000) | Out-Null
}
Start-Sleep -Seconds 3
```

- [ ] **Step 2: Launch the probed build in the background**

Run as a PowerShell command with `run_in_background: true`:

```
$env:ACDREAM_DAT_DIR   = "$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 *>&1 | Tee-Object -FilePath "launch-buga-postfix.log"
```

- [ ] **Step 3: Tell the user to walk the 5 scenarios + close**

Tell the user:

> Bug A fix landed. Launch is in the background. Please walk these 5 scenarios (about 30 seconds each):
>
> 1. **Cottage entry** (outdoor to indoor).
> 2. **Indoor standstill** about 10 seconds. Acceptance: stable, no flicker.
> 3. **2nd-floor walking** (the one that was broken). Acceptance: no stuck-falling when brushing upper floor edges.
> 4. **Cellar descent**.
> 5. **Single-floor cottage walk** (M1 regression check).
>
> Close the window when done.

- [ ] **Step 4: Read + analyze the post-fix log**

When the user reports the window is closed (or the background command notification arrives), convert and grep the log:

```
Get-Content launch-buga-postfix.log -Encoding Unicode | Out-File launch-buga-postfix.utf8.log -Encoding utf8
```

Then in Bash:
```
echo "=== [cp-write] caller distribution (post-Bug-A) ==="
grep -oE 'caller=[A-Za-z_.:0-9]+' launch-buga-postfix.utf8.log | sort | uniq -c | sort -rn | head -15
echo ""
echo "=== [indoor-walkable] lines (expect ZERO) ==="
grep -c '\[indoor-walkable\]' launch-buga-postfix.utf8.log
echo ""
echo "=== Transition.ValidateWalkable cp-writes (expect dramatic drop) ==="
grep -c 'caller=Transition\.ValidateWalkable' launch-buga-postfix.utf8.log
echo ""
echo "=== indoor-bsp result distribution ==="
grep -oE '\[indoor-bsp\].*result=[A-Z]+' launch-buga-postfix.utf8.log | grep -oE 'result=[A-Z]+' | sort | uniq -c
```

Expected:
- `[indoor-walkable]` count: **0** (the probe line was deleted).
- `Transition.ValidateWalkable` cp-write count: dramatic drop from the pre-fix 370 (pre-Bug-B saw 224+146 from indoor synthesis HIT path + outdoor fallthrough). Post-Bug-A should see only the outdoor terrain calls that legitimately fire when the player IS outdoors, perhaps tens of calls.
- BSP `FindCollisions:1615` + `StepSphereDown:1123` (Path 3 + 4 BSP-internal writes): unchanged or similar to post-Bug-B counts. These are the legitimate retail-path CP writers.
- `PhysicsEngine.ResolveWithTransition:583`: unchanged (per-tick seed still fires).

- [ ] **Step 5: Deliver the assessment to the user**

Tell the user one of the following based on their visual report:

**Success path:**
> Visual verification clean. `[indoor-walkable]` probe gone (expected — deleted). `Transition.ValidateWalkable` cp-write count dropped from 370 to N. Stuck-falling symptom resolved per user report. Bug A closed. Indoor ContactPlane retention phase complete (2 slices: Bug B [world-origin], Bug A [synthesis removal]).

**Partial success (Bug A resolves stuck-falling, but a new "one-frame flicker" appears on outdoor->indoor transitions or after teleport):**
> Visual verification mostly clean, but a one-frame flicker on outdoor->indoor transitions. This is R2 (spec section) — acceptable for now. File as follow-up issue if it becomes annoying.

**Failure path (stuck-falling persists):**
> Visual verification shows stuck-falling unchanged. Hypothesis was wrong — the per-frame synthesis was not the dominant cause, or there's a deeper issue with the OK-path retention. Investigate by adding a `[ci-cp-final]` probe at the bottom of `FindTransitionalPosition` to capture what `ci.CP` actually IS when the resolver finishes the OK case. Hand off as a separate session.

---

## Self-Review

Run after writing this plan:

**1. Spec coverage:**
- Spec section "Fix > Code changes" → Tasks 1 (synthesis call) + 2 (method + constant deletion). Covered.
- Spec section "Fix > Test changes" → Task 3. Covered.
- Spec section "Acceptance criteria > Probe-equivalence" → Task 6 step 4. Covered.
- Spec section "Acceptance criteria > Visual verification" → Task 6 steps 2-3. Covered.
- Spec section "Acceptance criteria > M1-baseline regression check" → Task 6 step 3 scenario 5. Covered.
- Spec section "Risks" → R1/R2/R3 mitigations live as falsification language in Task 6 step 5. R4 is "decision noted in spec, no action needed."
- Spec section "Out of scope" → not implemented. Acceptable.

**2. Placeholder scan:** No TBD/TODO. Every step has concrete commands + expected output.

**3. Type consistency:** No new types introduced; everything is a deletion. Existing names (`TryFindIndoorWalkablePlane`, `INDOOR_WALKABLE_PROBE_DISTANCE`, `FindEnvCollisions`, `BSPQuery.FindWalkableSphere`) are spelled consistently.

**4. Build-order discipline:** Task 1 leaves source-only code compiling (helper has no callers but still defined). Task 2 deletes the helper, breaking the test build. Task 3 deletes the tests, restoring build green. Task 4 confirms baseline. The temporary RED state between Tasks 2 and 3 is intentional and noted in Task 2 Step 3.