Mutation Gate Spike Verdict

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Mutation gate works; Task 12 per-test attribution is GO

Supersedes an earlier draft of this file that wrongly reported a "Stryker 9.6.1 OptionsValidator regression". There is no regression — the mutation gate runs fine. The earlier failure was operator error (see the gotcha below). This note corrects the record and captures the real spike verdict.

Task 12 spike verdict — GO (Plan A, killedBy)

Ran a scoped Stryker mutation on open-sse/utils/error.ts (2 covering test files) on the v3.8.29 toolchain (Stryker 9.6.1 + ajv 8.18.0, coverageAnalysis: perTest, tap-runner):

• 422 mutants — 86 Killed, 64 Survived, 272 NoCoverage.
• All 86 killed mutants carry a populated killedBy (86/86), and the report's testFiles section resolves each killedBy id to a covering test file.
• So per-test (Plan A) attribution works: Onda 2 radiography can read killedBy directly. Granularity is per test FILE (the tap-runner spawns one node process per test file) — exactly the unit the redundancy heuristic needs ("a test file that kills no mutant another file does not already kill").

The full config also instruments cleanly: npx stryker run --dryRunOnly reports "Found 8 of 5632 file(s) to be mutated. Instrumented 8 source file(s) with 15488 mutant(s)" — the 8-module nightly is healthy. This matches (and refreshes, on the current deps) the GO recorded back in v3.8.27.

⚠️ Gotcha that caused the false alarm: stryker -c is --concurrency, NOT --config-file

npx stryker run -c stryker.conf.json sets concurrency = "stryker.conf.json" (a string), which fails schema validation with a mis-attributed error: Config option "concurrency" must match pattern "^(100|[1-9]?[0-9])%$". Stryker still loads the real config via auto-discovery, so the run looks like the config is broken when it is not. jsPropertySyntax (an ajv-6 option, a no-op under ajv 8) makes the validator's error path unhelpful, but the data is the giveaway: options.concurrency === "stryker.conf.json".

Correct invocations:

• Default config (stryker.conf.json in cwd): npx stryker run (no flag).
• Explicit config file: pass it as the positional arg — npx stryker run my.conf.json.
• -c / --concurrency takes a number or percentage (-c 4, -c 50%).

Standing Onda-2 blocker (unchanged): budget, not tooling

The real blocker for a complete nightly remains runtime budget — the 8-module run is 15488 mutants and the god-files (chatCore, combo) dominate ~⅔; the conc=4 nightly timed out at 180min (run 27705123780). Levers: exclude god-files until the Onda-3 splits, seed the incremental file, batch per night, or accept partial. The per-test spike does not change that — it only confirms the attribution mechanism Onda 2 will rely on.