Router: harden route_patterns.py against malformed data + close CLI/symlink/name-invariant test gaps

[wz-gsa]

QA/security/vestigial review of scripts/route_patterns.py (+ generate_index, validate_frontmatter, tests). Security path-traversal guard is solid (verified: absolute, .., and subdir-symlink escapes all rejected; yaml.safe_load everywhere; no eval/format/shell injection; trusted --request-file vs untrusted INDEX-path asymmetry correctly enforced). Scoring/tie-breaker/determinism are correct. The gaps are robustness + test coverage.

SHOULD-FIX

1. _extract_frontmatter has no try/except (route_patterns.py:132-138). Sibling copies in generate_index/validate_frontmatter catch yaml.YAMLError; this one doesn't. One malformed on-disk SKILL.md referenced by INDEX raises ParserError out of load_candidates and DoSes routing for every request. Wrap in try/except yaml.YAMLError: return {}.

2. build_route crashes on priority: null (route_patterns.py:388-389). .get("priority", 50) returns None when the key is present-but-null → -None TypeError. Use .get("priority") or 50.

3. Malformed INDEX shapes raise AttributeError/ValueError (load_candidates :152-159, route_request). Bare-string entry, string routing, list-shaped frontmatter, or list-shaped top-level all crash. Guard with isinstance checks.

4. --json always exits 0 (:509-511), even on {"error":...} / primary: null. Non-JSON path correctly returns 1. Makes --json unusable as a CI gate. Return 1 if error or no primary.

5. apply_delegation demotes the delegator even when the delegate target is non-viable (:356-375). If A delegates to B and B is deprecated/zero-match, A is still demoted → route returns primary: null, discarding the correct answer. Only demote when the target is itself included and score > 0.

Test gaps (confirmed absent)

6. main() / CLI / --json / --request-file entirely untested (the trusted-vs-untrusted path distinction has zero coverage).
7. Path guard not tested with a real symlink inside a subdirectory (only a top-level link is tested).
8. name == id == dirname invariant not tested (ties to Skills: align SKILL.md frontmatter with the Agent Skills standard (require name + description; enforce name==dirname) #277).

NITs

• 5 near-duplicate extract_frontmatter copies (already drifted — that drift IS Epic: Repository Bootstrap #1). Consolidate.
• assumptions key always empty (dead scaffolding) — populate or remove.
• --explain advertised in the module docstring but not implemented (argparse errors on it). Add or delete the doc example.
• validate_request doesn't validate collection (request-side typo silently ignored).

Reachability, determinism, engine primitives, delegation happy-path, phrase-hit guard are all well covered (73 tests pass) — no action there.

AI-assisted (OpenCode); subagent-reviewed. Requires human review.