docs: add T8 (CRT shader fails to compile) + verified headless SwiftShader recipe

TODO.md

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+# TODO — Wings of the 90s
+
+Working notes from the 6 Oct 2026 audit. Everything below was measured by running the
+code, not inferred from the README. Upstream: `mac-ai-playground/retro-flight-sim`
+(read-only for `kevinhermes`); work happens in this fork.
+
+## Status check (verified)
+
+- `npm install` + `npm run build` — clean, 13 modules, 512 kB bundle, 581 ms.
+- `npm test` — passes, but see T4: it only counts braces.
+- Terrain is deterministic across instances (`getHeightAt(317,-812)` identical in two
+  separate `Terrain` objects) — the "persistent world" claim holds.
+- Rendering **verified in software** (SwiftShader, see "How to run it headless" below):
+  WebGL 2 context, 60 fps, 143 distinct colours, 63,792/64,000 non-black pixels, HUD
+  canvas drawing 6,905 lit pixels. No GPU is involved — this LXC has no `/dev/dri` and no
+  `/dev/nvidia*`, so all rendering is CPU-rasterised.
+- **T8 found during that verification**: the CRT post-processing shader does not compile,
+  so the 3D canvas renders pure black on any machine. See T8.
+
+---
+
+## T1 — Takeoff does not work (highest priority)
+
+Simulated 40 s at full throttle against the real `Terrain` heightmap:
+
+| t (s) | knots | alt (ft) | onGround |
+|------:|------:|---------:|:--------:|
+| 0 | 0.3 | 19.7 | false |
+| 1 | 23.2 | 2.8 | false |
+| 2 | 49.3 | 0 | true |
+| 6 | 340.2 | 12.2 | false |
+| 9 | 542.5 | 105.2 | false |
+| 10 | 564.6 | 0 | true |
+| 39 | 2,543.3 | 0 | true |
+
+The aircraft becomes briefly airborne, then never leaves the ground and accelerates to
+Mach 4.1. Causes:
+
+- `js/flight-model.js:77` — ground friction is `-hSpeed * 20`, i.e. 20 N per m/s,
+  against `maxThrust = 50000` N on a 1200 kg airframe. Friction loses every argument.
+- `js/flight-model.js:60-64` — lift is applied while `onGround`, scaled only by
+  `GROUND_LIFT_REDUCTION`, so the plane floats off the runway at arbitrary speed and
+  then the ground-collision clamp at `:95` slams it back down.
+- No weight-on-wheels state: `onGround` is a position test, not a contact state, so
+  there is no normal force and no way to model a proper rotation/tail-up.
+- `PITCH_LIMIT = 85°` and the auto-levelling at `:134-135` (`x *= 0.995`, `z *= 0.985`)
+  fight the player continuously.
+
+**Acceptance criteria:** full throttle from rest → airborne within a plausible
+takeoff roll (order 200–400 m), climb sustained, stall if nose raised too high, and
+speed bounded near a sane VMO instead of 2,500 kt.
+
+## T2 — No WebGL fallback
+
+`js/main.js:36-43` constructs `THREE.WebGLRenderer` with no try/catch. On a machine
+without WebGL the page throws an uncaught `Error creating WebGL context` and the loading
+screen never advances — a blank screen with no message.
+
+**Fix:** wrap renderer init, show a period-appropriate failure card ("GRAPHICS CARD NOT
+DETECTED"), and keep the loading/menu screens usable without 3D.
+
+## T3 — Stall speed is defined but unused
+
+`STALL_SPEED = 25` (`js/flight-model.js:4`) is used only to scale lift. Nothing in
+`hud.js` or `sound.js` references stalling. A period-accurate sim of this era should
+shove a warning in your face.
+
+**Fix:** stall flag on the flight model → HUD warning + stick shaker / audio cue.
+
+## T4 — The test suite is theatre
+
+`scripts/check-syntax.js` checks that each file is >10 chars and that `{` and `}` counts
+match. It cannot catch T1. CI (`.gitea/workflows/*.yml`) runs it on every push, so the
+green tick currently means nothing.
+
+**Fix:** real unit tests on `FlightModel` (takeoff profile, stall, ground contact) and
+`Terrain` (determinism, airport flattening radius). Node has `node:test` built in — no
+new dependency needed. Add a headless smoke test that asserts the game reaches the
+`FLIGHT` state.
+
+## T5 — No LICENSE
+
+README and repo carry no licence. Decide one (MIT matches the sibling `wings88`) and add
+the file.
+
+## T6 — No save/load
+
+The sibling project's brief promised persistent worlds. There is no persistence here —
+no `localStorage`, no world seed stored. Terrain is deterministic per process, which is
+not the same thing.
+
+**Fix:** persist the world seed + aircraft state; add a save/load menu entry.
+
+## T8 — The CRT shader does not compile, so the 3D canvas is black
+
+Found by running the game under software WebGL, not by reading the code. `js/retro.js:29`:
+
+```glsl
+gl_Position = vec4(position, 0.0, 1.0);
+```
+
+In three.js `position` is a **vec3**, so this asks for `vec4(vec3, float, float)` — five
+components into a four-component vector. Invalid GLSL ES on both WebGL 1 and 2:
+
+```
+THREE.WebGLProgram: Shader Error 0 - VALIDATE_STATUS false
+Program Info Log: Vertex shader is not compiled.
+ERROR: 0:71: 'constructor' : too many arguments
+```
+
+The whole post-processing pass therefore fails and the game canvas reads back as **one
+colour, 0/64,000 non-black pixels**. Verified in isolation: `vec4(vec3, float)` compiles,
+`vec4(vec3, float, float)` does not, on both WebGL 1 and WebGL 2.
+
+**Fix (verified):** `gl_Position = vec4(position.xy, 0.0, 1.0);` — compiles clean, and the
+canvas then reports 143 distinct colours, 63,792/64,000 non-black pixels, scanline banding
+visible every 25 rows, and the scene hash changing frame to frame once the aircraft moves.
+Applied locally during the audit to confirm it, then reverted — not committed.
+
+Note this is the kind of bug the current test suite cannot see (see T4): braces balance
+perfectly.
+
+## T7 — Minor / housekeeping
+
+- `index.html` requests `/favicon.ico` → 404 on every load. Add one, or drop the request.
+- Bundle is 512 kB (132 kB gzipped); Vite warns about the 500 kB chunk. Fine for now,
+  worth a `manualChunks` split if it grows.
+- `package-lock.json` is 31 kB for a two-dependency project — expected, just noting it.
+- No FPS cap. The README brags about a retro feel; `wings88`'s design notes suggest a
+  configurable 20 FPS cap, which would be cheap to add and very on-theme.
+
+---
+
+## How to run it headless (no GPU, verified working)
+
+This LXC has no GPU access — `lspci`/`lsmod` inside an LXC report the **Proxmox host's**
+hardware (an RTX 3090 shows up), but the container has no `/dev/dri` and no `/dev/nvidia*`,
+so nothing is usable. Software rendering is the only option and it does work.
+
+The combination that works:
+
+```bash
+CHROME=/root/.cache/ms-playwright/chromium-1234/chrome-linux64/chrome
+$CHROME --headless=new --no-sandbox --disable-gpu-sandbox \
+        --use-angle=swiftshader --enable-unsafe-swiftshader \
+        --remote-debugging-port=9223 --user-data-dir=/tmp/probe --no-first-run
+# then attach with playwright-core: chromium.connectOverCDP('http://127.0.0.1:9223')
+```
+
+Gotchas, all learned the hard way:
+
+- **Playwright's own launcher defeats this.** `chromium.launch()` injects defaults
+  (`--disable-gpu` among them) that silently kill the GPU process; every attempt via
+  `launch()` returned `webgl: NULL` or crashed the page. Launch Chrome directly and attach
+  over CDP instead.
+- `--use-gl=swiftshader` (legacy path) crashes the page. Use `--use-angle=swiftshader`.
+- `--use-angle=vulkan` + Mesa lavapipe (`VK_DRIVER_FILES=/usr/share/vulkan/icd.d/lvp_icd.json`)
+  brings the GPU process up (`GPU.EstablishGpuChannel` records samples) but still yields no
+  WebGL context. SwiftShader is the path that works.
+- Headful under `xvfb-run` crashes the page. `--headless=new` is required.
+- `--dump-dom` races the page script — it captures before the probe writes its result.
+- WebGL clears the drawing buffer after each frame (`preserveDrawingBuffer: false`), so a
+  synchronous `readPixels` returns all-black. Sample inside a `requestAnimationFrame`
+  callback, or the measurement is meaningless.
+- `readPixels` origin is bottom-left; flip rows before reporting them as screen rows.
+- Screenshots via CDP fail here (`Unable to capture screenshot`), so verification is by
+  pixel readback and colour histograms rather than images.
+
+---
+
+## Suggested order
+
+T1 → T4 (tests first would be better, but T1 is the reason the project is worth keeping)
+→ T2 → T3 → T5 → T6 → T7.
+
+## Notes on provenance
+
+Two commits, both authored by `mac-container-dev` on 5 May 2026. Not a fork of `wings88`
+(`fork: false`, no cross-references in code) — an independent take on the same brief.
+`wings88` has 214 source lines and no Three.js usage at all; its useful parts are the
+Jest/Playwright setup and the design guidelines (16–32 colour palette, no anti-aliasing,
+20 FPS cap), which would slot in here.