Throughput in the info overlay: grains per second and backing-up glow (t49)

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

docs/agent-log.md

@@ -4,6 +4,20 @@ 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.
 
+## 2026-10-27: t49 throughput overlay (Claude Code)
+
+- The I overlay also shows grains per second at each line's open outlet, an orange glow on
+  transport blocks that are loaded but not moving, and the rate in the hover. `src/sim/flow.js`
+  counts block-edge crossings per carrier block while `flowOn` (set by the I toggle) and folds
+  them into a smoothed per-second rate once a second. Hooks: `carryColumn`, `machinesTick` screws,
+  `screenNudge`, uphill cleat runs (only runs that commit), and the uphill face drag.
+- Not counted: bars. Not built: money per minute.
+- Files: `src/sim/flow.js`, `src/manifest.json`, `src/sim/conveyors.js`, `src/sim/machine-tick.js`,
+  `src/sim/slope-conveyors.js`, `src/sim/tick.js`, `src/render/overlays.js`, `src/ui/loop.js`,
+  `src/ui/input.js`, `src/ui/info.js`, `src/ui/notebook.js`, `test/t_flow.js`, `docs/PROJECT_MAP.md`.
+- Tests: `test/t_flow.js` (including a check that counting changes nothing in the simulation);
+  `python3 test/run_all.py --browser` all passed.
+
 ## 2026-10-27: cooled magma visible and drillable (Claude Code)
 
 - Owner report: bag magma in a brick box left invisible basalt that couldn't be picked up,