Corrección: fix(qa): report failing field and reason on evidence validation (Fixes #375) (#376) #377

Source PR: #376
Branch: fix/375-qa-evidence-schema-discovery
Head reviewed: e006021

Push the fixes to the branch above; do not open a new pull request. Comment on the PR and on this issue when done.

Blocking findings

• file_not_found diagnostic is unreachable; a missing evidence file reports file_unavailable (internal/cli/doctor.go:345): readQAFile collapses every os.Stat failure into fmt.Errorf("request is not a bounded regular file") (internal/cli/doctor.go:476). That error is a plain errors.New value with no Unwrap and no *PathError, so both os.IsNotExist(err) and errors.Is(err, os.ErrNotExist) evaluated at line 345 are always false: the branch is dead code. Control falls through the two statErr == nil checks (which also fail for a missing path) and reaches the final else, printing evidence_field=path evidence_reason=file_unavailable. The PR body's Runtime Harness item 6 states as verified that a nonexistent file emits evidence_field=path evidence_reason=file_not_found, and the new CLI test TestQARunEvidenceDiagnosticAttribution (internal/cli/qa_test.go:396) covers none of the four read-phase reasons, so nothing catches the mismatch. The whole point of qa run --evidence record schema is undiscoverable: bare invalid_request and no schema docs #375 is accurate attribution of the failing input; a typo in a path is the most common way to hit this path and it is the one case that reports the wrong reason.
  • Failure scenario: cortex qa run --role requirements-analyst --request request.txt --catalog ./catalog --evidence ./missing.json (path does not exist) -> stderr ends with evidence_field=path evidence_reason=file_unavailable. The claimed and documented file_not_found reason is never emitted for any input, because readQAFile's stat error is unwrapped and both not-exist predicates are false.

Acceptance criteria

• Fixed: file_not_found diagnostic is unreachable; a missing evidence file reports file_unavailable (internal/cli/doctor.go:345). The scenario below no longer reproduces: cortex qa run --role requirements-analyst --request request.txt --catalog ./catalog --evidence ./missing.json (path does not exist) -> stderr ends with evidence_field=path evidence_reason=file_unavailable. The claimed and documented file_not_found reason is never emitted for any input, because readQAFile's stat error is unwrapped and both not-exist predicates are false.