booth/persistent-memory.d/2026-09-24-r3-seam-pass-what-only-it-could-see.md

The r3 seam pass: what only it could see

2026-09-24. Contract docs/contracts/r3_compare.contract.md (design-dev); althing thread 01M3952NCDRRJX5XDFSPMSP5HJ.

design-dev's heid contract panel read r3 cold. Our seam pass read it against the real app.py, items.py, base.html and view.html, plus small probes on a scratch booth. It found 12 mismatches, all folded before a line of code. The build then went through heid code-review and bug-hunt, and our own gate, with nothing structural left. design-dev: "S4 and S8 would each have cost a round."

The ones worth remembering, because they recur

• data-region ids must be unique on a page. The in-place client's swap() in base.html keeps only the FIRST fresh node for each id, then replaces EVERY live node that has that id with a copy of it. Two per-side regions sharing an id would make B's flag button a copy of A's after any save, so pressing B flags A, with nothing to show it happened. Also: do not key a region by rel (a pair with a == b duplicates it) and do not prefix it item- (swap reads a missing item-* as a stale tile, not a reload). This is a mechanical rule that belongs in CLAUDE.md; it is not there yet.
• Moving code breaks mutation anchors. 21 of r2c's 24 view.html rows were anchored inside the inline script that r3 moved to _stage_js.html, and mutation_check.py fails a row whose anchor is gone. A contract that moves code must list the re-pointed rows in its "Assertions that change" table, and gate on the table still falsifying, not only on the suite staying green.
• "404 the way view does" was two rules, and neither was view's. A missing f is a 422 from FastAPI (required str), not a 404; declare = "" and 404 by hand. booth_items follows symlinks, so a link pointing outside the booth is IN review_chain, while view 404s it through resolve plus containment. Compare needed the conjunction.
• Route order. /b/{name}/{filepath:path} is a catch-all; a new /b/{name}/<word> route must register before it. A booth file literally named <word> becomes unreachable (accepted, as for view/marks/asks/embed.json).
• A resolve done twice is a race. After the merge, the review route checked f and then resolved the whole ring again, so cring.index(f) could raise (a 500) when a file vanished in between. design-dev's d54bb04 judges each rel once per request.