Screw conveyors join across the corner to diagonals (t62)

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

docs/agent-log.md

@@ -4,6 +4,21 @@ 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: t62 screw conveyor joins (Claude Code + Codex)
+
+- Straight screws touching a diagonal's end only at the corner now join, in both looks and in
+  ghosts/previews, and grains and bars cross the joint. Same-row joins were already elbows.
+  Also removed the seam across the top of connected elbows in the smooth look.
+- Files: new `src/render/diagonal-screws.js` (join and casing geometry moved out of
+  `src/render/world.js`), `src/render/smooth-shaders.js`, `src/ui/previews.js`,
+  `src/sim/conveyors.js` (`straightScrewNext`), `src/sim/machine-tick.js`, `src/sim/items.js`,
+  `src/manifest.json`, `docs/PROJECT_MAP.md`, `tools/scenes/t62-joins.js`, tests
+  `test/t_diag_screws.js`, `test/t_smooth.py`.
+- Tests: `python3 test/run_all.py --browser` all passed; determinism diff showed only timing
+  lines and the new checks.
+- Open: the corner join doesn't check that the straight piece ends there, so a straight run
+  passing over the diagonal's corner also draws a jog. Not playtested by hand.
+
 ## 2026-10-27: t66 dev console in every build (Claude Code)
 
 - Owner decision: the console ships in production too, with a warning when it's turned on that