Tianyi Cui
605587e79c
Add a second axis to every RFC — its class (feature, bug-fix,
simplification, architecture, process, testing) — encoded in the path
as docs/rfc/{lifecycle}/{class}/file.md. The folder is the label, so
the closed set is enforced by structure rather than a parsed field.
Two new doc-sync gates back it:
- verify-rfc-classification: every RFC sits in a valid class folder and
the README index lists it under the matching lifecycle→class heading.
- verify-doc-refs: every docs/*.md path cited in a packages|examples TS
comment resolves — closes a drift class verify-md-links can't see, and
catches the four comment refs this reorg moved.
The README gains a Classification section explaining the taxonomy and
per-class index sub-sections. A self-referential process RFC records why
the scheme is path-encoded and gated.
29 lines
1.7 KiB
Markdown
29 lines
1.7 KiB
Markdown
# RFC: Mutation testing as the coverage counterweight
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Status: proposed
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<!-- XXX: legacy ADR/RFC body format, not yet normalized to a unified RFC template. -->
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## Problem
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The per-file 100% coverage gate ([the quality-gates decision](../../implemented/process/2026-06-11-quality-gates.md)) proves every line *executes* under test — not that any assertion would notice if the line were wrong. Under agent-written tests, coverage pressure can produce execution-without-assertion. Mutation testing measures what coverage cannot: whether the suite *kills* deliberately injected bugs.
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## Proposal
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Stryker (`@stryker-mutator/vitest-runner`) over `packages/*/src`:
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- **PR-scoped incremental runs** (changed files only) as a CI job — fast enough to gate merges once tuned.
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- **Nightly full runs** with a tracked mutation score; start by recording, then set the threshold at the observed baseline and ratchet upward (same policy as coverage: thresholds only ever tighten).
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- Surviving mutants are work items: an agent picks a survivor, writes the killing test, repeats — a well-shaped autonomous loop.
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- Equivalent mutants (provably behavior-preserving) get annotated exclusions with reasons, mirroring the `/* v8 ignore */` policy.
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## Plan
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1. Add Stryker config scoped to one package (llm — smallest, most algorithmic) and measure runtime.
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2. Expand to all packages; record baseline scores in the config.
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3. Wire the nightly job; add the incremental PR job once runtime is acceptable.
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## Risks
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Runtime: mutation testing is expensive; per-file 100% coverage helps (every mutant is at least reached). If PR-scoped runs stay too slow, keep them nightly-only and rely on the score ratchet.
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