fix #130: doorway-slice scissor cut the aperture's top/right pixel row

The user's "thin strip of background color along the TOP outer edge of a
doorway, looking out from inside" is the landscape-slice scissor box, not
the W=0 clip port.

Mechanism (pinned headlessly, Issue130DoorwayStripTests, 147 eye/gaze
combos at the real Holtburg A9B4 0x0170 exit door):
- BeginDoorwayScissor converted the slice NDC AABB to pixels as
  Floor(origin) + Ceiling(size). The far edge floor(min)+ceil(max-min)
  lands up to ONE PIXEL SHORT of the true top/right edge at unlucky
  fractional alignments (captured: top edge y=0.7938 @1080p -> row 968
  cut; right edge column 1296 @1920 cut).
- The scissor brackets the ENTIRE landscape slice (sky, terrain, outdoor
  statics, weather). The exit-portal SEAL stamps the full raw aperture at
  true depth and the shell wall ends at the aperture edge, so the cut row
  never receives any color write -> clear color, flickering with eye
  movement as the fractional alignment shifts.
- This violated AD-17's own invariant (over-inclusion is safe,
  UNDER-inclusion is the bug class). No register change: the fix restores
  the row's documented doctrine.

Lead 1 (987313a W=0 clip port regression) REFUTED by the same harness:
the CPU polygon pipeline (ProjectToClip -> ClipToRegion merges ->
ClipPlaneSet planes) is sub-pixel exact against the raw aperture
projection (worst 0.54 px, 0.00 px aligned). For an all-in-front doorway
polygon the port is bit-identical to the old 1e-4 path by construction.
The EyeInsidePortalOpening rescue stays deleted.

Fix: conservative outer bound floor(min)/ceil(max) extracted to
NdcScissorRect.ToPixels (GL-free; containment property proven in the
header comment); BeginDoorwayScissor delegates.

Pins:
- NdcScissorRectTests: center-inside containment across 251 fractional
  alignments x 2 framebuffer sizes + both captured regression cases.
- Issue130DoorwayStripTests: production flood + assembler at the real
  exit door; asserts the scissor never cuts a plane-admitted fragment
  (worstScissorGap 0.00 px post-fix, was 10.8 px capped) and the CPU
  pipeline stays sub-pixel exact (canary 1.2 px).

Suites: App 252+1skip / Core 1439+2skip / UI 420 / Net 294 green.
Awaiting the user visual gate at a cottage doorway.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/ISSUES.md

@@ -4512,38 +4512,45 @@ math).
 
 ## #130 — Background-color strip along the TOP outer edge of a doorway when looking out from inside
 
-**Status:** OPEN
+**Status:** FIX SHIPPED — awaiting user visual gate
 **Severity:** LOW-MEDIUM (small strip, but on the most-stared-at pixels in the game)
-**Filed:** 2026-06-12 (user report, post-#119-close session; "also NOW" —
-possibly new since the W=0 clip port `987313a`)
-**Component:** render — doorway aperture edge (seal/punch/OutsideView seam)
+**Filed:** 2026-06-12 (user report, post-#119-close session)
+**Component:** render — doorway-slice scissor box math (AD-17 family)
 
 **Symptom (user):** standing inside looking out through a doorway, a
 thin strip of background (clear/world) color runs along the OUTER edge
 of the TOP of the doorway opening.
 
-**Leads (capture first — plausibly a `987313a` regression):**
-1. The W=0 port changed `ProjectToClip` (exact w>=0, no 1e-4 epsilon)
-   and DELETED the `EyeInsidePortalOpening` rescue — the OutsideView
-   region through a near doorway is computed slightly differently now.
-   If the OutsideView's top edge sits ~1 px BELOW the aperture's drawn
-   shell edge, terrain/outdoor geometry isn't drawn in that strip while
-   the interior seal/punch still cleared it → background color.
-   Suspects within the port: `MergeSubPixelVertices` shaving a top
-   vertex; the exact-w boundary vs the old epsilon shifting the
-   projected edge; the deleted rescue no longer substituting the full
-   view for an eye-pressed doorway.
-2. The interior SEAL depth vs the shell top edge (the #118-era
-   machinery) — a 1-px mismatch between the seal polygon and the shell
-   aperture would show the clear color exactly at an edge.
+**Root cause (pinned headlessly 2026-06-12, `Issue130DoorwayStripTests`
+— 147 eye/gaze combos at the real A9B4 0x0170 exit door):** the
+`BeginDoorwayScissor` NDC→pixel conversion (`Floor(origin) +
+Ceiling(size)`) put the box's far edge at `floor(min)+ceil(max−min)` —
+up to ONE PIXEL SHORT of the true top/right edge at unlucky fractional
+alignments. The scissor brackets the ENTIRE landscape slice (sky,
+terrain, statics, weather), the seal stamps the full aperture at true
+depth, and the shell ends at the aperture edge — so the cut pixel row
+never receives color: a background strip along the top edge that comes
+and goes as the eye moves (alignment shifts). Captured live by the
+harness: top edge y=0.7938 at 1080p → row 968 cut; right edge column
+1296 cut at 1920. This violated AD-17's own doctrine (over-inclusion
+safe, under-inclusion is the bug class).
 
-**Next:** screenshot + [viewer]/[pv-dump] capture at a doorway showing
-the strip; diff the OutsideView top edge NDC vs the aperture polygon's
-projected top edge for that frame (the CornerFloodReplay harness
-machinery can replay the frame headlessly once the eye/cell are
-captured). If it reproduces at the same doorway with `987313a` reverted
-locally, it's the port's edge math; fix the math, never re-add the
-rescue.
+**Lead 1 REFUTED:** the W=0 clip port `987313a` is exonerated by the
+same harness — the CPU polygon pipeline (ProjectToClip → ClipToRegion
+merges → ClipPlaneSet planes) is sub-pixel exact against the raw
+aperture projection (worst 0.54 px; 0.00 px in the aligned case). For
+an all-in-front doorway polygon the port is bit-identical to the old
+path by construction (the W clip pass only runs when a vertex has
+w < 0).
+
+**Fix:** conservative outer bound `floor(min)/ceil(max)` extracted to
+`NdcScissorRect.ToPixels` (GL-free, unit-tested); `BeginDoorwayScissor`
+delegates. Pins: `NdcScissorRectTests` (containment property + both
+captured alignments) + `Issue130DoorwayStripTests` (scissor never cuts
+plane-admitted fragments; CPU-pipeline exactness canary ≤1.2 px).
+
+**Gate:** stand inside any cottage, look out the door, sweep the gaze —
+no background strip at the top edge at any alignment.
 
 ---