Screw tubes carry bars, one whole bar at a time

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

docs/agent-log.md

@@ -4,6 +4,29 @@ 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.
 
+## 2026-10-24: screw tubes carry bars (Claude Code, with Codex)
+
+Note: "how do you transport bars? belts work but tubes do not, should they?" The owner chose
+tubes over a separate bar lift.
+
+- `src/sim/items.js`: a bar whose eight cells are all tube cells is in the tube (derived from
+  its position, so saves need nothing new). On the tube beat it steps along the tube, snaps
+  into the next block's lane at corners, and leaves a mouth with a launch like grains. A bar
+  pushed by a belt into a tube's side or back, falling into a down tube or sitting on an up
+  tube's intake enters when the aligned cells are free. Grains and bars wait for each other.
+  Gas and liquid don't block a bar (Claude added this after review: smoke near furnaces stalled
+  bars in Codex's version).
+- Text: `pieces.js` tube description, `notebook.js`, `docs/DESIGN.md`, `docs/PROJECT_MAP.md`.
+- Tests: `t_conveyors` (55 checks): belt into a lift and out the top, right tube, up-to-right
+  and right-to-down corners, blocked mouth waits without overlap, grains and a bar share a
+  lift with sand conserved, save mid-tube, smoke and steam in the tube, melting in a tube,
+  bars still ride and stop on belts and rest on top of sideways tubes. All 11 headless suites
+  and `play.py` (131) pass; `t_smooth.py`'s half-resolution check failed on the slow fallback
+  (known flaky).
+- Shots: `tools/scenes/bar-lift.js`, `shots/bar-lift-{300,900}.png`: mold, belt, lift, corner,
+  belt; the bars arrive at the top.
+- Open: nothing.
+
 ## 2026-10-23: screw tubes use all their lanes (Claude Code, with Codex)
 
 Note: "maybe the belts can move faster/carry more than the tubes… the tubes only carry one line of