chore(agents): add test-audit skill for contributor test-quality gating

.agents/skills/build-from-issue/SKILL.md

@@ -377,7 +377,7 @@ Read the relevant source files before making changes. Implement step by step per
 
 ### Step 9: Write Tests
 
-Write tests as specified in the plan's Test Plan section. Follow the project's existing test conventions.
+Write tests as specified in the plan's Test Plan section. Follow the project's existing test conventions. Before adding or changing a test, apply the `test-audit` skill's authoring gate so new coverage protects an independent contract instead of re-asserting the implementation.
 
 #### Unit tests
 

.agents/skills/review-github-pr/SKILL.md

@@ -137,6 +137,12 @@ Read through the full diff (and the PR description if available). Produce a summ
   - Do not fabricate concerns or claim a behavioral regression without evidence
     for both the prior and proposed behavior.
 - **Agent infrastructure**: When the PR changes behavior, commands, or development workflows, use the `sync-agent-infra` maintenance map to check that related skills were updated. When it adds, removes, or renames skills or crates; changes workflow relationships or skill coverage; modifies issue or PR templates; or changes agent cross-references, apply the full consistency checklist. Report missing companion updates or drift under **Potential Concerns**.
+- **Test quality**: When the PR adds or changes tests, apply the `test-audit`
+  skill's junk-pattern checks to the diff. Report an assertion-free probe,
+  implementation-coupled test, mock-only coverage of a dependency a real
+  integration test could exercise cheaply, or near-duplicate coverage under
+  **Potential Concerns** when it creates a concrete risk, rather than
+  duplicating `test-audit`'s detailed criteria here.
 
 ## Step 5: Output
 

.agents/skills/sync-agent-infra/SKILL.md

@@ -32,6 +32,7 @@ Detect and fix drift across the agent-first infrastructure files. These files re
 - After adding, removing, or renaming a crate in `crates/`
 - After changing workflow chain relationships between skills
 - After changing which product or development areas a skill covers
+- After changing test-authoring or test-audit guidance
 - After modifying issue or PR templates
 - Before opening a PR that touches any of the above
 
@@ -56,6 +57,7 @@ Use this map when product behavior, commands, or development workflows change. I
 | Security review or remediation workflow | `review-security-issue`, `fix-security-issue` |
 | RFC template, numbering, or lifecycle | `create-rfc` |
 | Documentation structure, navigation, or doc-update workflow | `update-docs-from-commits` |
+| Test authoring, test-quality gating, or junk-test patterns | `build-from-issue`, `review-github-pr` |
 | Skills, crates, workflow chains, issue/PR templates, or agent cross-references | `sync-agent-infra` |
 
 ## Prerequisites
@@ -142,6 +144,7 @@ For each file in the table above, check for the following inconsistencies:
 4. **`create-spike`** — Reference to `build-from-issue` as next step must be accurate.
 5. **`review-security-issue`** / **`fix-security-issue`** — Cross-references between the two must be accurate.
 6. **PR creation and review checks** — The `create-github-pr`, `review-github-pr`, `build-from-issue`, and `principal-engineer-reviewer` references to `sync-agent-infra` must exist and use trigger conditions aligned with this skill.
+7. **Test-audit routing** — `build-from-issue` and `review-github-pr` must route test authoring and review to the `test-audit` skill's authoring gate and junk-pattern checks without copying its detailed criteria.
 
 ### Skill Layout, Metadata, and Portability