This is a small code-hardening change in src/domain/spend.ts: the lossy sanitizing of run ids into file names is replaced by a fail-closed validation regex, so two distinct run ids can no longer collide into one spend file. No content/ records, citations, assessments, or provenance labels are touched, and no citation identifiers appear. AGENTS.md is untouched, so §3.15's reservation is not engaged. Rather than weakening a check, the change strengthens accounting integrity and path-traversal safety (rejecting '../escape'), consistent with §8's 'no silent data repair'. Tests are added covering the verbatim-name case, rejection of a slash and a path escape, and that recordSpend throws without creating directories, satisfying §8/§10. Nothing in the PR body asks me to do anything beyond reviewing; the session link and attribution are ordinary provenance noise.

The change strengthens fail-closed spend accounting by rejecting run IDs that are not already safe file names instead of lossily mapping distinct IDs to the same path. The tests cover verbatim naming, slash and traversal rejection, and refusal before any spend directory or row is created. It neither edits AGENTS.md nor changes content, citations, assessments, or publication provenance, and it does not weaken or evade the constitutional checks.

The change replaces a lossy sanitization regex in spendRunFile with strict, fail-closed regex validation (/^[A-Za-z0-9][A-Za-z0-9._-]{0,199}$/), preventing collisions or path traversal in spend ledger filenames as requested in review note #316. The implementation adheres to code rules (§8) and fail-closed operational principles (§3.15) without altering content or AGENTS.md.

The diff only tightens spend ledger file naming: run ids must already match a safe file-name regex or are refused before any row is written, replacing the prior lossy underscore mapping that could collide distinct ids. No AGENTS.md edit, no content/citations, no confidence material, and no weakening of §3.15 checks—the change strengthens fail-closed accounting. Tests cover a real id, slash/path-escape refusal, and that recordSpend creates nothing on a bad id. Complete diff with no runs or omitted files; ordinary code hygiene under §8.

This is a small, fail-closed hardening of the spend-ledger check: instead of lossily sanitizing unsafe run ids into file names (which let two distinct ids collide on one ledger file), it now refuses any id that is not already a file name, and no AGENTS.md or §3.15 check is touched. If anything it strengthens a check rather than weakening one — path escapes like '../escape' and ids with slashes now throw before any row is written, and the tests cover refusal, verbatim naming, and that recordSpend creates nothing on refusal. The change is confined to src/domain/spend.ts and its test file, with no citations, content, or provenance claims involved, so the epistemic rules are not engaged.