* test(#2978): roadmap validate must perform structural validation
Failing-first: roadmap validate returns {"warnings":[]} (exit 0) for every
input — empty file, garbage, missing file, truncated frontmatter — because it
performs no structural validation and its one opt-in check (W021 milestone-
prefix) is off by default. Six cases: empty, garbage, missing, truncated
frontmatter, well-formed (no false positive), BOM-prefixed (not corruption).
* fix(#2978): add structural validation to roadmap validate
roadmap validate returned {"warnings":[]} (exit 0) for every input — empty
file, garbage, missing file, truncated frontmatter — because it performed no
structural validation and its one opt-in check (W021 milestone-prefix) is
off by default. A verb named validate that cannot produce a negative result
provides false assurance.
Add four structural checks, each producing a coded warning {code, message}:
- V001: file missing/unreadable (was silent success)
- V002: empty/whitespace-only
- V003: malformed frontmatter (unterminated --- fence; BOM-tolerant per #3057)
- V004: no recognizable phase entries (no ### Phase N: heading)
Keep the existing W021 milestone-prefix check as-is. Exit non-zero via
ExitError(1) when warnings are non-empty, per the documented contract
('exits non-zero on any error or warning'). Well-formed roadmaps (incl.
BOM-prefixed, CRLF) still validate cleanly with warnings: [] and exit 0.
* test(#2978): update W021 tests for non-zero exit on warnings
Two existing W021 tests asserted roadmap validate exits 0 even with warnings
('roadmap validate should exit 0 even with warnings') — that was the bug.
#2978 made validate exit non-zero on any warning (per its documented
contract). Updated both mismatch-case tests to expect success===false and
parse the JSON output from the failure path (stdout is written before the
ExitError throw).
* chore(#2978): add changeset fragment
* chore(#2978): backfill changeset PR number 3092
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Co-authored-by: sim <sim@local>
