Step 19 of v4.1 — extend-in-place per brief Preferences. Three new test
blocks asserting forward-compat:
1. Legacy fixtures (plan-run-A.md, plan-run-B.md) — without profile_used
in frontmatter — still parse cleanly after manifest-yaml.mjs added
OPTIONAL_STRING_KEYS.
2. New fixtures (profile-plan-run-{economy,premium}-*.md) — with
profile_used in frontmatter — parse cleanly with correct profile
value extracted.
3. Real v4.1 plan (.claude/projects/2026-05-08-voyage-v4.1-modellprofiler/plan.md)
validates strict, emits no PLAN_VERSION_MISMATCH warning.
Tests: 475 pass + 2 skipped (Docker not installed).
Adds 6 files in tests/synthetic/ exercising the determinism pipeline at the
SC7 brief floor (Jaccard >= 0.833). Plan fixture pair: 40 step titles each
with 38 shared (Jaccard 0.905). Review fixture pair: 30 finding-IDs each
with 28 shared (Jaccard 0.875). Reuses lib/parsers/jaccard.mjs +
lib/parsers/finding-id.mjs.
The new pair coexists with tests/lib/review-determinism.test.mjs which
holds the older SC4 (0.70) floor against tests/fixtures/ultrareview/.
The lower floor protects pipeline regressions; the higher floor anchors
the speedup brief's determinism aspiration.
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