Build range follows the screen; out-of-range replace ghosts replace (t64)

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

docs/agent-log.md

@@ -4,6 +4,19 @@ 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: t64 build range about the screen; out-of-range replace ghosts (Claude Code)
+
+- `setBuildRange`/`inBuildRange` in `src/sim/tools.js`: the UI sets the view box each frame
+  (`src/ui/loop.js`); half-sizes clamped to REACH..BUILD_MAX (64..200 grains); with no view (tests)
+  a REACH box around the bot. Used by `blockInReach`, machine/mold placement and previews,
+  right-click take-back, hover reach, and ghost building for blocks, machines and molds.
+- A replace (G) placed beyond range stores a replace flag on the ghost (`[code, v, extra, 1]`);
+  `ghostTick0` removes the old piece (refunded) and places the new one (charged), or re-sets a
+  filter's settings, when the bot comes in range.
+- Files: `src/sim/tools.js`, `src/sim/blocks.js`, `src/sim/undo.js`, `src/ui/actions.js`,
+  `src/ui/previews.js`, `src/ui/info.js`, `src/ui/loop.js`, `test/t_build.js`, `docs/DESIGN.md`,
+  `docs/PROJECT_MAP.md`. Tests: `python3 test/run_all.py --browser` all passed. Not played by hand.
+
 ## 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