feat(B-0170.4): seed convention-drift fixture + regression test

[AceHack]

Summary

5th eval-set fixture for the substrate-claim-checker. Covers the convention sub-class of the 7-class verify-then-claim taxonomy via a self-contained fixture pair (current ADR + sibling predecessor ADR support file). Synthetic exemplar; anchor PR #2512 (the PR that shipped check-convention.ts).

Continues the B-0170.4 eval-set thread:

• PR feat(B-0170.4): seed eval-set fixture for count-drift regression coverage #3611 — count-drift fixture
• PR feat(B-0170.4): seed existence-drift fixture + regression test #3624 — existence-drift fixture
• PR feat(B-0170.4): seed path-form-drift fixture + regression test #3696 — path-form-drift fixture
• PR feat(B-0170.4): seed cross-surface-drift fixture + regression test #3749 — cross-surface-drift fixture
• this PR — convention-drift fixture

Remaining check-types for B-0170.4 thread completion: semantic-equivalence-drift, empirical-output-drift, self-recursive-drift (none yet shipped as checkers).

Files

• tools/substrate-claim-checker/fixtures/convention-drift-no-reciprocal-marker.md (new) — current ADR claiming supersession
• tools/substrate-claim-checker/fixtures/_convention-drift-target-adr.md (new) — predecessor ADR support file (leading-underscore marks "fixture support, not a top-level fixture")
• tools/substrate-claim-checker/fixtures/README.md — fixture-index row added
• tools/substrate-claim-checker/fixtures.test.ts — regression test added; pins exact finding count (1), claim line (36), target path, and reason substring ("not reciprocated", "Superseded by")

The fixture pair is self-contained: check-convention.ts's 3-root resolution (fileDir / parentDir / repoRoot) finds the support file via fileDir without dragging in any real repo ADR pair.

Per PR #3611 review-thread discipline, the fixture's HTML-comment provenance intentionally avoids restating the literal Supersedes ADR ... claim so a regression in body-claim detection cannot be masked by a comment-side match.

Focused checks

• bun test tools/substrate-claim-checker/fixtures.test.ts → 5 pass / 0 fail / 30 expects
• bun test tools/substrate-claim-checker/ (full suite) → 117 pass / 0 fail / 274 expects (6 files)
• Direct CLI run: bun tools/substrate-claim-checker/check-convention.ts tools/substrate-claim-checker/fixtures/convention-drift-no-reciprocal-marker.md → exits 1 with 1 convention-drift finding(s) on line 36 with reciprocal-marker reason string
• Tree-count canary: git ls-tree HEAD = 53 entries (matches origin/main)

Test plan

• Focused fixture test passes
• Full substrate-claim-checker suite passes
• Direct CLI invocation reports expected finding shape
• No commit-tree corruption (53 root entries vs 53 on main)

Composes with

• B-0170 (parent backlog row)
• PR feat(B-0170): add ADR supersession convention checker #2512 (anchor — check-convention.ts shipped)
• PRs feat(B-0170.4): seed eval-set fixture for count-drift regression coverage #3611 / feat(B-0170.4): seed existence-drift fixture + regression test #3624 / feat(B-0170.4): seed path-form-drift fixture + regression test #3696 / feat(B-0170.4): seed cross-surface-drift fixture + regression test #3749 (sibling B-0170.4 eval-set fixtures)

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds the fifth empirical eval-set fixture to tools/substrate-claim-checker, covering the convention drift checker (ADR supersession reciprocity) and wiring a regression test to ensure the checker continues to flag the missing reciprocal “Superseded by” marker pattern.

Changes:

• Added a self-contained convention-drift fixture pair (current ADR + predecessor support ADR) under tools/substrate-claim-checker/fixtures/.
• Extended fixtures.test.ts with a regression test that pins exact finding shape (count, claim line, target path, reason substrings).
• Updated the fixtures index README to include the new convention-drift fixture row.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tools/substrate-claim-checker/fixtures/README.md	Adds the convention-drift fixture row to the eval-set index.
tools/substrate-claim-checker/fixtures/convention-drift-no-reciprocal-marker.md	New “current ADR” fixture containing a Supersedes ADR \...`` body claim.
tools/substrate-claim-checker/fixtures/_convention-drift-target-adr.md	New predecessor ADR support file intentionally missing the reciprocal “Superseded by” marker.
tools/substrate-claim-checker/fixtures.test.ts	Adds a convention-drift regression test that asserts exact finding count/line/target/reason substrings.