Attribution (dat-evidenced, supersedes the misplaced-cell hypothesis):
the phantom staircase is the Holtburg MEETING HALL (AAB3 building[0],
model 0x010014C3 at AAB3-local (36,84,116)), NOT an A9B3 building - the
user stood at the A9B3/AAB3 boundary (cell-transit trail in
issue112-gate1.log) and clicked through the hall to the NPC behind it.
The hall's interior stair cells (0x100..0x106, ring climbing z 116->124.5
to the deck hatch) have geometry coincident with the shell's west wall
(both at local x=29.0). Our outdoor per-building flood admits them with
CORRECT tight clip regions (4-6 planes, door-aperture NDC boxes -
Issue113MeetingHallFloodTests proves it), but DrawEnvCellShells drew them
WHOLE: mesh_modern.vert writes gl_ClipDistance from the routed CellClip
slot, and gl_ClipDistance is ignored unless GL_CLIP_DISTANCEi is enabled -
which no caller ever did for the shell pass (born inert in 1405dd8).
Interior staircase painted across the exterior wall; unpickable because
it is cell geometry, not an entity.
Retail oracle: cell geometry IS clipped to the accumulated portal view -
Render::set_view (:343750) installs the view polygon edge planes,
DrawEnvCell submits every cell polygon with planeMask=0xffffffff (:427922)
through ACRender::polyClipFinish. Characters/meshes are NOT poly-clipped
(viewconeCheck path) - entity routing stays cleared, comment scoped.
Fix: enable GL_CLIP_DISTANCE0..7 around exactly the shell pass
(self-contained per feedback_render_self_contained_gl_state; no early-outs
between set and restore). Slot-0 fallback slices (>8-plane regions) still
draw pass-all - the assembler's scissor fallback remains unimplemented and
documented; the new flood test pins 0 such slices at the hall.
Refuted along the way (full evidence in Issue113PhantomStairsDumpTests):
- ONE misplaced interior EnvCell unifying #113+#112+collision gaps: all 17
A9B3 cottage cells share an identical dat Position (nothing to misplace);
the #112 gap is a real 20cm doorway micro-gap 0.23m outside threshold
cell 0x104 (straddles its exterior portal plane at foot radius 0.48);
missing object collision remains #99/A6.P4.
- A9B3 dat content near the spot: no stair geometry in shell (balcony at
z119 + turret roof only), cells (flat 116/118.8), statics, or stabs.
Tests: Core 1389 green (+6 dump facts) / App 224 (+1 flood replay) /
UI 420 / Net 294; pre-existing 4 #99-era failures unchanged.
Visual gate pending: user re-check of the hall west face vs retail.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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