Belts carry 4 grains deep; stalled belts warn and stop animating (t45)

docs/agent-log.md

@@ -4,6 +4,23 @@ What agents have done, newest first. Add an entry for every piece of work: the d
 note or request it was for, what changed, the files touched, the tests run, and anything left
 open or not verified. Keep each entry short; the git history has the details.
 
+## 2026-10-29: t45 belt depth and visible transport stalls (Codex)
+
+- Four-grain belt bed; local half-second jam warnings, hover advice and frozen/resuming
+  animation in both looks, including screws, screens, bars and whole cleated runs.
+- Files: sim/{conveyors,machine-tick,slope-conveyors,transport-status,items,tick,world},
+  render/{cell,slope-belts,overlays,gpu/{draw,smooth,smooth-shader,smooth-slope}},
+  ui/{info,loop}, manifest; test/{t_stalls.js,t_stalls.py,t_conveyors,t_threads,fixtures/t45-loop},
+  tools/experiments/belt-depth.js, docs/{DESIGN,TESTING,PROJECT_MAP}, task and this log.
+- New checks fail on original code; all 42 headless suites pass. Browser t_stalls.py,
+  play.py, t_smooth.py and t_gpu.py pass with host GPU; sandbox startup timed out.
+  Fixed GPU pan/zoom clock-buffer recreation caught by t_gpu.py. Worker counts 0/1/2/8
+  match cells and jam/clocks. Inspected shots/t45-stalled{,-smooth}.png. Map regenerated.
+- Normal feed 30.0 -> 30.0, heavy 360.0 -> 90.0 grains/s; uphill 78.8. Preserved the
+  separate 96-cell cleat push bound. Updated lift fixture to the chosen four-grain bed;
+  retained its 90% comparison, conservation and all-lane checks. Worldgen untouched.
+  No open blockers; full browser suite not run. Ready for owner review; no commit.
+
 ## 2026-10-29: t89 custom game cursors (Codex)
 
 - Finished interrupted work: hollow build arrow at the exact mouse, open coloured crosses for