Proof chain health signal

Inline return type instead of named interface: `work.ts:744` — `Promise<{ runs: number; callouts: number }>` is an anonymous object type. If other consumers ever need these counts (e.g., a JSON output mode for `work complete`), this shape would need to be extracted into a named interface. Low priority — the function is internal and has one call site.

A008/A009 tag collision with prior feature: `work.test.ts:423` — Tags `@ana A008, A009` exist from a previous feature's contract (configurable branchPrefix). Pre-check tools that grep for `@ana A008` will find both. No functional impact today, but as tag density grows, disambiguation may be needed (e.g., feature-scoped tag namespaces).

No test exercises nonzero callout counts: Both test paths (single entry and existing chain) produce `0 callouts` because neither fixture includes callouts in the verify report or prior chain entry. A test with a fixture that has actual callouts would exercise the accumulation arithmetic beyond `0 + 0`. The `reduce` logic is correct by inspection (`(e.callouts || []).length` summed), but it's untested with nonzero values.

chalk.gray verified only by absence of failure: The spec requires `chalk.gray()` wrapping (constraint). The tests confirm the text content but not the styling — chalk strips ANSI in non-TTY. This is standard for CLI tests and not a gap per se, but the chalk.gray requirement is verified by code reading (`work.ts:1107`), not by test assertion.

Contract A008/A009 block names imply unit tests: Contract blocks "returns chain health counts" and "returns cumulative callout counts with existing chain" suggest direct unit assertions on the return value (`result.runs equals 1`). The builder used integration tests instead, which is the right call since `writeProofChain` is internal. But the contract's `target: result.runs` / `matcher: equals` framing doesn't match `toContain` on console output. Future contracts for internal functions could use `target: output` to match the actual test approach.