D236 pass 10: refute "nondeterministic instantiation", it's room occlusion

Per the rule-2-clarification pass-10 brief in findings.md, applied the new
three-bucket taxonomy to D280's leading theory that the 0x0c184b50
discrete-tree-card render-mode class instantiates inconsistently across
runs of the deterministic -level_36 boot (~4 tris vs ~720).

Added a small env-gated diagnostic (GE_D236RM, port/fast3d/gfx_pc.cpp
gfx_sp_tri1) counting that class's per-frame triangle count, heartbeat-
logged every 300 frames even at zero. Three independent -level_36
launches (one with sustained GE_INPUTSCRIPT camera rotation) produced
byte-identical per-frame counts, falsifying the "run-to-run dependent"
premise outright. Cross-referencing with the existing GE_D104 room-census
probe in the same run shows the count drops to zero at the exact frame
the player's curRoom transitions from 12 (17-20 rooms drawn, an outdoor
vista) to 18 (1-5 rooms, an enclosed indoor space) via the boot's own
scripted intro camera — ordinary portal/room occlusion, not a bug. None
of buckets (a)/(b)/(c) apply; no src/game or port/ fix made or warranted.

The original "wall not discrete sprites" symptom is untouched by this
pass — narrowed the real next step to getting a camera into room 12
facing the tree line directly, in docs/dev/findings.md.

Added the generalisable "deterministic boot flag != deterministic camera
path" quirk to porting-notes.md §E. findings-index.csv regenerated.

docs/dev/GE-ENV-PROBES.md

@@ -56,6 +56,7 @@ Two classes:
 | `GE_TEXDUMP` | `port/fast3d/gfx_pc.cpp:1020`, `port/fast3d/gfx_opengl.cpp:700` | PPM dump of every uploaded texture + a `fmt/siz/palfmt/palidx/pal[0..3]` line. Root-caused D161 (Depot ceiling). Kept as an inert diagnostic. | **live** (RC3 not finished) |
 | `GE_D116` | `port/fast3d/gfx_pc.cpp:1710,2362`, `src/game/textrelated.c:265,541` (cached `ge_d116`) | HUD/text "X-mirror" (D114/D116) vbo/uv trace. **D114/D116 CLOSED — NOT A BUG (M-33/D168): the captures were upside-down, not mirrored.** Probe is now dead scaffolding — strip on the next cleanup pass. | dead (D114/D116 closed) |
 | `GE_D288` | `port/fast3d/gfx_pc.cpp` (`gfx_sp_tri1`, right after the D233 trivial-reject guard; cached `ge_d288`) | M-152 diag for the Silo intro stray triangle: logs any triangle whose clip-space NDC bbox covers >15% of the screen or goes non-finite, with each vertex's `w` and `any_behind_camera`. **Investigation in progress** — narrowed to two candidates (an unguarded `w`-division NaN leak in the backface-cull test just below, or the D106/D271 portal-BFS family), not yet root-caused; needs a live/headless `-level_20` run to disambiguate. | **live** (D288) |
+| `GE_D236RM` | `port/fast3d/gfx_pc.cpp` (`gfx_sp_tri1`, unconditional getenv, no state kept when unset) | M-155/pass-10 diag for D236: per-frame (`num_dls`) triangle count of the `0x0c184b50` render-mode class (`other_mode_l` exact match), heartbeat-logged every 300 frames even at zero. **REFRAMED D280's "run-to-run dependent instantiation" as ordinary room-based occlusion**, not a CPU-side gating bug — see `## D236` pass-10 writeup. | **live** (D236 OPEN, kept for future passes) |
 
 ## Dxx diagnostic probes — finding closed unless noted