[systemfsoftware-maker]

Summary

A CompileError reason now points at the line where the error is in that mutant's own code; before, any mutant other than the last in a batched check could report a line computed from a different mutant's text. Each check span also reports how much compiler work the check cost, which the parity lane in the next layer reads to compare this branch's checker with main's.

This is layer 1 of 4 of the TypeScript 7 native checker stack (base main). Layers 2 to 4 add the parity lane, the type-query port and the edit-location shortcut. Plan: docs/plans/2026-10-09-2106-perf-typescript-checker-tsgo-native-plan.md.

What changes

• Docs (U1). The README states the TypeScript floor the checker already enforces (>=7.0.0), and a changeset corrects the 8.1.0 release note that said importers are re-checked "only when the mutant changes what that file exports" (they are re-checked whenever the mutated file has no compile errors of its own).
• Own positions (U2, R14, KTD3, AE10). A CompileError reason now names the line and column in that mutant's own text. Diagnostics are rendered inside checkOne while that mutant's snapshot is current; before, Checker.cell rendered them after the whole call, against the last mutant's text, so an earlier mutant in the same call could report a wrong line (the AE10 fixture reported line 16 instead of 20).
• Counts (U3, R3, KTD6). Each typescript-checker.compiler.check span reports the compiler work it did: snapshot updates, parenthesized re-splices, TCE emit builds and emit time. No new span names.

Checker verdict statuses do not change. Only the (line,col) inside a reason can change, and only for a mutant that was not the last one in its call.

Tests and the mutants they target

Main's mutation report: run 37960922409, artifact mutation-report-416.

• src/__tests__/check-mutants.workflow.property.test.ts, new property ∀diagnostics_FailedReason_≡RenderedLinesJoinedByNewline, kills dogfood mutant 47892392410b616f (check-mutants.workflow.ts, join separator). Checked against the mutant: PropertyRefuted within 100 runs; passes on the real code. The existing OwnRenderedDiagnostics property survives that mutant because it never draws two diagnostics.
• tests/check-mutants.integration.test.ts, scenario "An earlier mutant of one call reports the line its own text put it on", with fixture tests/__fixtures__/per-mutant-position/. It fails on the pre-U2 code (brokenLine 16, expected 20) and passes after. ts-compiler.handle.ts and Checker.cell.ts are outside the dogfood mutate globs (stryker.config.ts:12-19 mutates src/**/*.workflow.ts and src/**/*.schema.ts), so they have no mutant ids.
• U3 has no package test (Test Admission refused it as wiring). Layer 2's parity lane refuses a branch side that checks mutants but reports zero snapshot updates, so a tally that never gets set fails there.

Local verification (targeted, per supervisor ruling S1)

• pnpm --filter @systemfsoftware/stryker-js-typescript-checker typecheck: exit 0.
• pnpm --filter @systemfsoftware/stryker-js-typescript-checker test: 31 files / 193 tests passed. Full suite after U3: two program-digest.integration.test.ts cases timed out under host load average ~140, then passed on a rerun of that file (193/193).
• No local corpus, e2e or mutation run. CI runs those.

How an agent consumes this

• Span typescript-checker.compiler.check (OTLP, OTEL_ENABLED=true), numeric attributes (OTLP JSON: counts arrive as intValue strings; typescript.tce.ms is usually fractional and arrives as doubleValue):
  • typescript.counts.schema_version: 1. Gate on this before reading the others. Main's checker emits the span without any of these attributes.
  • typescript.snapshot_updates.count: updateSnapshot calls in this check call (a parenthesized re-splice counts its own update).
  • typescript.resplices.count: mutants re-spliced as (replacement) because the bare splice changed the parse.
  • typescript.tce_builds.count: tsc emit builds this call ran for TCE (at most one per file that has passing mutants).
  • typescript.tce.ms: wall time of those builds, summed.
  • typescript.importer_shortcut.count: always 0 in this layer; layer 4's edit-location shortcut sets it.
  • The existing typescript.diagnostics.count, typescript.compile_errors.count and typescript.tce.* attributes are unchanged.
• Verdict reason: unchanged format <file>(<line>,<col>): <severity> TS<code>: <text>, one line per diagnostic, joined by \n. (line,col) is 1-based and refers to the text the compiler checked for the mutant the verdict belongs to. When that mutant needed the parenthesized fallback splice, a column on the replacement's line counts the added (.
• No new reason codes or artifacts in this layer. The lane artifacts and reason codes come in layer 2.

Review and overlap

• ce-code-review (focused: correctness plus one local adversarial read; no cross-model CLI on the host) on head 09236eeaa: Ready to merge, two P3 advisory findings, both ruled:
  • P3, the literal importer_shortcut.count 0: Accepted for this layer as documented. Layer 4 (feat(stryker-js-typescript-checker): skip importer re-checks for edits inside function bodies #286) replaces it with the real count and asserts it is above 0 on a shortcut-eligible fixture and 0 under importerCheck: 'always'.
  • P3, the fallback-splice column note above: Accepted as documented, no change. Positions refer to the checked text, and parity already exempts own-file positions.
• CI on 8e7d07378 (main 3cb134232 with fix(e2e): keep day-old releases out of the fixture bake and bound each install #284 merged in): CI run 38069489915 is all green, including check and the five e2e legs (lifecycle, sabotage, rest-1, rest-2, svelte-composite). Nix, Changeset Check and Commitlint are green.
• This branch touches packages/stryker-js-typescript-checker/README.md and tests/check-mutants.integration.test.ts, which Stream A's refactor(repo)!: move every Layer out of service ports into driver modules #261 also changes. Whoever lands second merges the other.

Changesets

• typescript-checker-ts7-only-docs.md (patch): README floor and 8.1.0 note correction.
• typescript-checker-own-positions.md (patch): U2.
• typescript-checker-check-counts.md (patch): U3.

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

[ryanleecode]

Root verified: all checks green on e22a2fa except the bench enterprise-fixture leg (setup-timed-out, an inherited lane defect Stream G owns); 0 threads, up to date with main, no suppressions.