refactor: ship uses shared test coverage audit

Replace 135 lines of inline Step 3.4 methodology with
{{TEST_COVERAGE_AUDIT_SHIP}}. Functionally identical output plus:
- E2E test decision matrix (marks paths needing E2E vs unit)
- Eval recommendations for LLM prompt changes
- Regression detection iron rule
- Test framework detection via CLAUDE.md first
- Test plan artifact for /qa consumption

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.agents/skills/gstack-ship/SKILL.md

@@ -574,6 +574,27 @@ If multiple suites need to run, run them sequentially (each needs a test lane).
 
 100% coverage is the goal — every untested path is a path where bugs hide and vibe coding becomes yolo coding. Evaluate what was ACTUALLY coded (from the diff), not what was planned.
 
+### Test Framework Detection
+
+Before analyzing coverage, detect the project's test framework:
+
+1. **Read CLAUDE.md** — look for a `## Testing` section with test command and framework name. If found, use that as the authoritative source.
+2. **If CLAUDE.md has no testing section, auto-detect:**
+
+```bash
+# Detect project runtime
+[ -f Gemfile ] && echo "RUNTIME:ruby"
+[ -f package.json ] && echo "RUNTIME:node"
+[ -f requirements.txt ] || [ -f pyproject.toml ] && echo "RUNTIME:python"
+[ -f go.mod ] && echo "RUNTIME:go"
+[ -f Cargo.toml ] && echo "RUNTIME:rust"
+# Check for existing test infrastructure
+ls jest.config.* vitest.config.* playwright.config.* cypress.config.* .rspec pytest.ini phpunit.xml 2>/dev/null
+ls -d test/ tests/ spec/ __tests__/ cypress/ e2e/ 2>/dev/null
+```
+
+3. **If no framework detected:** falls through to the Test Framework Bootstrap step (Step 2.5) which handles full setup.
+
 **0. Before/after test count:**
 
 ```bash
@@ -636,9 +657,41 @@ Quality scoring rubric:
 - ★★   Tests correct behavior, happy path only
 - ★    Smoke test / existence check / trivial assertion (e.g., "it renders", "it doesn't throw")
 
+### E2E Test Decision Matrix
+
+When checking each branch, also determine whether a unit test or E2E/integration test is the right tool:
+
+**RECOMMEND E2E (mark as [→E2E] in the diagram):**
+- Common user flow spanning 3+ components/services (e.g., signup → verify email → first login)
+- Integration point where mocking hides real failures (e.g., API → queue → worker → DB)
+- Auth/payment/data-destruction flows — too important to trust unit tests alone
+
+**RECOMMEND EVAL (mark as [→EVAL] in the diagram):**
+- Critical LLM call that needs a quality eval (e.g., prompt change → test output still meets quality bar)
+- Changes to prompt templates, system instructions, or tool definitions
+
+**STICK WITH UNIT TESTS:**
+- Pure function with clear inputs/outputs
+- Internal helper with no side effects
+- Edge case of a single function (null input, empty array)
+- Obscure/rare flow that isn't customer-facing
+
+### REGRESSION RULE (mandatory)
+
+**IRON RULE:** When the coverage audit identifies a REGRESSION — code that previously worked but the diff broke — a regression test is written immediately. No AskUserQuestion. No skipping. Regressions are the highest-priority test because they prove something broke.
+
+A regression is when:
+- The diff modifies existing behavior (not new code)
+- The existing test suite (if any) doesn't cover the changed path
+- The change introduces a new failure mode for existing callers
+
+When uncertain whether a change is a regression, err on the side of writing the test.
+
+Format: commit as `test: regression test for {what broke}`
+
 **4. Output ASCII coverage diagram:**
 
-Include BOTH code paths and user flows in the same diagram:
+Include BOTH code paths and user flows in the same diagram. Mark E2E-worthy and eval-worthy paths:
 
 ```
 CODE PATH COVERAGE
@@ -659,9 +712,9 @@ USER FLOW COVERAGE
 [+] Payment checkout flow
     │
     ├── [★★★ TESTED] Complete purchase — checkout.e2e.ts:15
-    ├── [GAP]         Double-click submit — NO TEST
-    ├── [GAP]         Navigate away during payment — NO TEST
-    └── [★   TESTED] Form validation errors (checks render only) — checkout.test.ts:40
+    ├── [GAP] [→E2E] Double-click submit — needs E2E, not just unit
+    ├── [GAP]         Navigate away during payment — unit test sufficient
+    └── [★   TESTED]  Form validation errors (checks render only) — checkout.test.ts:40
 
 [+] Error states
     │
@@ -669,12 +722,16 @@ USER FLOW COVERAGE
     ├── [GAP]         Network timeout UX (what does user see?) — NO TEST
     └── [GAP]         Empty cart submission — NO TEST
 
+[+] LLM integration
+    │
+    └── [GAP] [→EVAL] Prompt template change — needs eval test
+
 ─────────────────────────────────
-COVERAGE: 5/12 paths tested (42%)
+COVERAGE: 5/13 paths tested (38%)
   Code paths: 3/5 (60%)
-  User flows: 2/7 (29%)
+  User flows: 2/8 (25%)
 QUALITY:  ★★★: 2  ★★: 2  ★: 1
-GAPS: 7 paths need tests
+GAPS: 8 paths need tests (2 need E2E, 1 needs eval)
 ─────────────────────────────────
 ```
 
@@ -686,6 +743,8 @@ If test framework detected (or bootstrapped in Step 2.5):
 - Prioritize error handlers and edge cases first (happy paths are more likely already tested)
 - Read 2-3 existing test files to match conventions exactly
 - Generate unit tests. Mock all external dependencies (DB, API, Redis).
+- For paths marked [→E2E]: generate integration/E2E tests using the project's E2E framework (Playwright, Cypress, Capybara, etc.)
+- For paths marked [→EVAL]: generate eval tests using the project's eval framework, or flag for manual eval if none exists
 - Write tests that exercise the specific uncovered path with real assertions
 - Run each test. Passes → commit as `test: coverage for {feature}`
 - Fails → fix once. Still fails → revert, note gap in diagram.
@@ -706,6 +765,37 @@ find . -name '*.test.*' -o -name '*.spec.*' -o -name '*_test.*' -o -name '*_spec
 For PR body: `Tests: {before} → {after} (+{delta} new)`
 Coverage line: `Test Coverage Audit: N new code paths. M covered (X%). K tests generated, J committed.`
 
+### Test Plan Artifact
+
+After producing the coverage diagram, write a test plan artifact so `/qa` and `/qa-only` can consume it:
+
+```bash
+source <(~/.codex/skills/gstack/bin/gstack-slug 2>/dev/null) && mkdir -p ~/.gstack/projects/$SLUG
+USER=$(whoami)
+DATETIME=$(date +%Y%m%d-%H%M%S)
+```
+
+Write to `~/.gstack/projects/{slug}/{user}-{branch}-ship-test-plan-{datetime}.md`:
+
+```markdown
+# Test Plan
+Generated by /ship on {date}
+Branch: {branch}
+Repo: {owner/repo}
+
+## Affected Pages/Routes
+- {URL path} — {what to test and why}
+
+## Key Interactions to Verify
+- {interaction description} on {page}
+
+## Edge Cases
+- {edge case} on {page}
+
+## Critical Paths
+- {end-to-end flow that must work}
+```
+
 ---
 
 ## Step 3.5: Pre-Landing Review