feat: requirements coverage gate in plan-phase pipeline (#984) (#1121)

Add step 13 (Requirements Coverage Gate) to plan-phase workflow.
After plans pass the checker, verifies all phase requirements are
covered by at least one plan before declaring planning complete.

- Extracts REQ-IDs from plan frontmatter and compares against
  phase_req_ids from ROADMAP
- Cross-checks CONTEXT.md features against plan objectives to
  detect silently dropped scope
- Reports gaps with options: re-plan, defer, or proceed
- Skips when phase_req_ids is null/TBD (no requirements mapped)

Fixes #984

Co-authored-by: TÂCHES <afromanguy@me.com>

CHANGELOG.md

@@ -12,6 +12,7 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
   - Pre-wave dependency check in `execute-phase`: verifies key-links from prior wave artifacts before spawning next wave
   - Cross-Plan Data Contracts (Dimension 9) in plan-checker: detects incompatible transformations between plans sharing data pipelines
   - Export-level spot check in `verify-phase`: catches dead stores that exist in wired files but are never called
+- **Requirements coverage gate in plan-phase** — New step 13 verifies all phase requirements are covered by at least one plan before planning completes. Cross-checks REQ-IDs from ROADMAP against plan frontmatter and CONTEXT.md features against plan objectives (#984)
 - **`/gsd:ship` command** — Native PR creation workflow that bridges local completion → merged PR. Auto-generates rich PR body from planning artifacts (SUMMARY.md, VERIFICATION.md, REQUIREMENTS.md), pushes branch, creates PR via `gh`, optionally requests review, and updates STATE.md with shipping status (#829)
 
 ### Fixed

docs/FEATURES.md

@@ -171,6 +171,7 @@
 - REQ-PLAN-06: System MUST support `--skip-research` flag to bypass research phase
 - REQ-PLAN-07: System MUST prompt user to run `/gsd:ui-phase` if frontend phase detected and no UI-SPEC.md exists (UI safety gate)
 - REQ-PLAN-08: System MUST include Nyquist validation mapping when `workflow.nyquist_validation` is enabled
+- REQ-PLAN-09: System MUST verify all phase requirements are covered by at least one plan before planning completes (requirements coverage gate)
 
 **Produces:**
 | Artifact | Description |

get-shit-done/workflows/plan-phase.md

@@ -587,11 +587,62 @@ Display: `Max iterations reached. {N} issues remain:` + issue list
 
 Offer: 1) Force proceed, 2) Provide guidance and retry, 3) Abandon
 
-## 13. Present Final Status
+## 13. Requirements Coverage Gate
+
+After plans pass the checker (or checker is skipped), verify that all phase requirements are covered by at least one plan.
+
+**Skip if:** `phase_req_ids` is null or TBD (no requirements mapped to this phase).
+
+**Step 1: Extract requirement IDs claimed by plans**
+```bash
+# Collect all requirement IDs from plan frontmatter
+PLAN_REQS=$(grep -h "requirements_addressed\|requirements:" ${PHASE_DIR}/*-PLAN.md 2>/dev/null | tr -d '[]' | tr ',' '\n' | sed 's/^[[:space:]]*//' | sort -u)
+```
+
+**Step 2: Compare against phase requirements from ROADMAP**
+
+For each REQ-ID in `phase_req_ids`:
+- If REQ-ID appears in `PLAN_REQS` → covered ✓
+- If REQ-ID does NOT appear in any plan → uncovered ✗
+
+**Step 3: Check CONTEXT.md features against plan objectives**
+
+Read CONTEXT.md `<decisions>` section. Extract feature/capability names. Check each against plan `<objective>` blocks. Features not mentioned in any plan objective → potentially dropped.
+
+**Step 4: Report**
+
+If all requirements covered and no dropped features:
+```
+✓ Requirements coverage: {N}/{N} REQ-IDs covered by plans
+```
+→ Proceed to step 14.
+
+If gaps found:
+```
+## ⚠ Requirements Coverage Gap
+
+{M} of {N} phase requirements are not assigned to any plan:
+
+| REQ-ID | Description | Plans |
+|--------|-------------|-------|
+| {id} | {from REQUIREMENTS.md} | None |
+
+{K} CONTEXT.md features not found in plan objectives:
+- {feature_name} — described in CONTEXT.md but no plan covers it
+
+Options:
+1. Re-plan to include missing requirements (recommended)
+2. Move uncovered requirements to next phase
+3. Proceed anyway — accept coverage gaps
+```
+
+Use AskUserQuestion to present the options.
+
+## 14. Present Final Status
 
 Route to `<offer_next>` OR `auto_advance` depending on flags/config.
 
-## 14. Auto-Advance Check
+## 15. Auto-Advance Check
 
 Check for auto-advance trigger: