[mkarlesky]

This PR applies approved decisions D1 (compiler strictness) and D3 (lint triage) from the findings report.

Stacked on #21.

Results:

• Lint: 121 findings down to 9. All 9 are the engine's synchronous I/O and sequential discovery, which PR C converts to async (D2).
• Tests: 254 unit (+3) and 4 integration, all passing.
• Coverage: unchanged at 68.5% of statements. This PR adds no coverage work; that's PR C.

D1: noUncheckedIndexedAccess for src/

The flag is on in tsconfig.json; tests keep their own config. All 34 compile errors are resolved:

• Mandatory regex groups go through a captured() helper, with a comment on why each is guaranteed.
• Fixed-length values become tuples.
• Real guards remain where an index can be missing.

The flag also removes the seven false alarms in which the linter called real runtime guards impossible.

It found a real bug. matchToProblem() checked group indexes against the array length, but a custom pattern's optional file group that didn't participate is undefined at an in-range index. That value reached path.normalize(), which threw, and the whole pattern's results were dropped. Two failing tests came first.

D3: lint triage

Fixes:

• SingleFlight dropped a rejection whose reason was undefined. It now records outcomes as a flag. A failing test came first.
• reparse() could reject unhandled. It runs from watchers and editor events without being awaited; it now catches and logs its own failures. The deliberate fire-and-forget refresh() calls are marked void.
• runPlan's untyped new Map() made the whole selection any. It's now typed.
• Untyped input is typed honestly. normalizePatterns() and readCppUnitReport() take unknown and narrow it, instead of trusting types that user JSON and parsed XML don't guarantee. Their shape checks are now meaningful to the compiler.
• Type escapes removed.
  • CeedlingRunner keeps the state it shares with its exit callback in one object, and its non-null assertions are gone.
  • The controller passes the TestController to its item builders instead of using this.controller!.
  • resolveLaunchConfig() returns a typed DebugConfiguration.
  • dispose() callbacks use block bodies.
• Smaller fixes: util.format for interpolated errors, import type, removal of redundant assertions and of the async on activate(), removal of the dead ProblemMatchingPattern re-export, and binary-search line lookup in discovery.

Marked inline with reasons:

• sequential awaits that are deliberate (the run plan, clean and clobber, SingleFlight);
• the synchronous /proc snapshot taken on cancellation;
• Unity's verbatim regex escape;
• split()'s undefined pieces, which the library typing hides;
• one TypeScript control-flow false positive.

Tuning: require-await is off for test doubles.

🤖 Generated with Claude Code