Multi-core simulation: grain movement and heat across a worker pool (t88 phase 3)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/TESTING.md

@@ -49,7 +49,7 @@ done();                                 // prints ALL PASS or N FAILED, sets the
 - A new suite named `test/t_<topic>.js` is picked up by `run_all.py` automatically.
 
 **Determinism.** The simulation's randomness comes from seeded generators. The same code and the
-same test give the same output every run, apart from lines with timings in ms. To prove a
+same test give outputs identical across thread counts and between runs, apart from lines with timings in ms. To prove a
 refactor changed nothing, save every suite's output before and after, and diff them:
 
 ```sh
@@ -58,6 +58,17 @@ for t in test/t_*.js; do node $t > /tmp/after/$(basename $t).txt; done    # afte
 diff -r /tmp/before /tmp/after
 ```
 
+`test/t_threads.js` runs the real shared-memory scheduler inline and with 1, 2 and 8
+Node workers, including repeats, comparing all mutable cell/chunk bytes and JS side effects.
+The browser creates up to `min(16, hardwareConcurrency - 2, CPU workers setting)` helpers.
+Small passes run inline; larger passes use batches to amortize dispatch. Wakes and heat flags
+merge after each pass; long liquid searches are deferred until that merge. Global machine and
+weather randomness remains separate from the chunk streams. World generation uses the same
+inline schedule while settling. The t88 re-baseline changes worldgen material hashes and the
+seeded sand pile bounds in `t_corner_seal.js`; the heat oracle now supports pass outputs.
+The conveyor fixture uses a wider feed pile, the screen fixture warms longer, and `t_load.js`
+checks waking within eight ticks separately from the probabilistic consumption of fuel.
+
 ## Browser tests
 
 - They need the `.venv` from README.md → Develop; plain `python3` switches to it on its own.
@@ -73,7 +84,8 @@ diff -r /tmp/before /tmp/after
   both looks at zoom 12 and 2. ImageMagick decodes RGB; the per-channel tolerance is 8,
   mean RGB error must stay below 0.5/255 and fewer than 0.3% of pixels may exceed 8
   (smooth AO/edge rounding). These are frozen pre-removal legacy images, not generated
-  from the new renderer. Inspect the matching `shots/golden-*.png` after visible changes.
+  from the new renderer. The compressed `golden-world-640x*.json.gz` fixtures retain the
+  Phase 2 world bytes that produced them, isolating renderer checks from worldgen RNG changes. Inspect the matching `shots/golden-*.png` after visible changes.
 - `test/t_gpu.py` checks default limits (four storage textures per stage), dirty-upload
   readback after 240 busy ticks with scrolling and both looks, exact dirty/full image equality
   with a frozen clock, world replacement, transparent overlays, drill contours, shader compilation timing, successful device recreation and failed recovery with
@@ -98,7 +110,7 @@ diff -r /tmp/before /tmp/after
 - `python3 tools/caps.py` prints isolation, actual WebGPU adapter info and the GL renderer for
   Chromium and installed Firefox. Real mode requires a hardware Chromium adapter.
 - `test/t_caps.py` checks absent, null, rejected and insufficient-limit adapters, notices and
-  the mandatory WebGPU startup gate. Threads remain optional until Phase 3. Firefox smoke
+  the mandatory WebGPU startup gate. Cross-origin isolation is required for threads. Firefox smoke
   checks that a browser without WebGPU shows the notice and cannot start a world.
 - Install Firefox with `.venv/bin/python -m playwright install firefox`.
   `python3 test/firefox_smoke.py` checks isolation and the WebGPU notice, starts a pixel world