diff --git a/src/resources/extensions/gsd/state.ts b/src/resources/extensions/gsd/state.ts
index f14f83ad5..dc09a9003 100644
--- a/src/resources/extensions/gsd/state.ts
+++ b/src/resources/extensions/gsd/state.ts
@@ -79,7 +79,12 @@ export async function getActiveMilestoneId(basePath: string): Promise<string | n
   for (const mid of milestoneIds) {
     const roadmapFile = resolveMilestoneFile(basePath, mid, "ROADMAP");
     const content = roadmapFile ? await loadFile(roadmapFile) : null;
-    if (!content) return mid; // No roadmap yet — milestone is incomplete
+    if (!content) {
+      // No roadmap — but if a summary exists, the milestone is already complete
+      const summaryFile = resolveMilestoneFile(basePath, mid, "SUMMARY");
+      if (summaryFile) continue; // completed milestone, skip
+      return mid; // No roadmap and no summary — milestone is incomplete
+    }
     const roadmap = parseRoadmap(content);
     if (!isMilestoneComplete(roadmap)) return mid;
   }
@@ -117,7 +122,12 @@ export async function deriveState(basePath: string): Promise<GSDState> {
   for (const mid of milestoneIds) {
     const rf = resolveMilestoneFile(basePath, mid, "ROADMAP");
     const rc = rf ? await loadFile(rf) : null;
-    if (!rc) continue;
+    if (!rc) {
+      // No roadmap — milestone is complete if it has a summary
+      const sf = resolveMilestoneFile(basePath, mid, "SUMMARY");
+      if (sf) completeMilestoneIds.add(mid);
+      continue;
+    }
     const rmap = parseRoadmap(rc);
     if (!isMilestoneComplete(rmap)) continue;
     const sf = resolveMilestoneFile(basePath, mid, "SUMMARY");
@@ -134,7 +144,18 @@ export async function deriveState(basePath: string): Promise<GSDState> {
     const roadmapFile = resolveMilestoneFile(basePath, mid, "ROADMAP");
     const content = roadmapFile ? await loadFile(roadmapFile) : null;
     if (!content) {
-      // No roadmap yet — treat as incomplete/active
+      // No roadmap — check if a summary exists (completed milestone without roadmap)
+      const summaryFile = resolveMilestoneFile(basePath, mid, "SUMMARY");
+      if (summaryFile) {
+        const summaryContent = await loadFile(summaryFile);
+        const summaryTitle = summaryContent
+          ? (parseSummary(summaryContent).title || mid)
+          : mid;
+        registry.push({ id: mid, title: summaryTitle, status: 'complete' });
+        completeMilestoneIds.add(mid);
+        continue;
+      }
+      // No roadmap and no summary — treat as incomplete/active
       if (!activeMilestoneFound) {
         activeMilestone = { id: mid, title: mid };
         activeMilestoneFound = true;
diff --git a/src/resources/extensions/gsd/tests/derive-state.test.ts b/src/resources/extensions/gsd/tests/derive-state.test.ts
index 4f485a718..210afbe78 100644
--- a/src/resources/extensions/gsd/tests/derive-state.test.ts
+++ b/src/resources/extensions/gsd/tests/derive-state.test.ts
@@ -618,6 +618,58 @@ Continue from step 2.
     }
   }
 
+  // ═══ Milestone with summary but no roadmap → complete ═══════════════════
+  {
+    console.log('\n=== milestone with summary and no roadmap → complete ===');
+    const base = createFixtureBase();
+    try {
+      // M001, M002: completed milestones with summaries but no roadmaps
+      const m1dir = join(base, '.gsd', 'milestones', 'M001');
+      mkdirSync(m1dir, { recursive: true });
+      writeFileSync(join(m1dir, 'M001-SUMMARY.md'), '---\nid: M001\n---\n# Bootstrap\nDone.');
+
+      const m2dir = join(base, '.gsd', 'milestones', 'M002');
+      mkdirSync(m2dir, { recursive: true });
+      writeFileSync(join(m2dir, 'M002-SUMMARY.md'), '---\nid: M002\n---\n# Core Features\nDone.');
+
+      // M003: active milestone with a roadmap
+      writeRoadmap(base, 'M003', '# M003: Polish\n## Slices\n- [ ] **S01: Cleanup**');
+
+      const state = await deriveState(base);
+
+      assertEq(state.phase, 'planning', 'summary-no-roadmap: phase is planning (active is M003)');
+      assertEq(state.activeMilestone?.id, 'M003', 'summary-no-roadmap: active milestone is M003');
+      assertEq(state.activeMilestone?.title, 'Polish', 'summary-no-roadmap: active title is Polish');
+      assertEq(state.registry.length, 3, 'summary-no-roadmap: registry has 3 entries');
+      assertEq(state.registry[0]?.status, 'complete', 'summary-no-roadmap: M001 is complete');
+      assertEq(state.registry[0]?.title, 'Bootstrap', 'summary-no-roadmap: M001 title from summary');
+      assertEq(state.registry[1]?.status, 'complete', 'summary-no-roadmap: M002 is complete');
+      assertEq(state.registry[1]?.title, 'Core Features', 'summary-no-roadmap: M002 title from summary');
+      assertEq(state.registry[2]?.status, 'active', 'summary-no-roadmap: M003 is active');
+      assertEq(state.progress?.milestones?.done, 2, 'summary-no-roadmap: milestones done = 2');
+      assertEq(state.progress?.milestones?.total, 3, 'summary-no-roadmap: milestones total = 3');
+    } finally {
+      cleanup(base);
+    }
+  }
+
+  // ═══ All milestones have summary but no roadmap → complete ═════════════
+  {
+    console.log('\n=== all milestones summary-only → complete ===');
+    const base = createFixtureBase();
+    try {
+      const m1dir = join(base, '.gsd', 'milestones', 'M001');
+      mkdirSync(m1dir, { recursive: true });
+      writeFileSync(join(m1dir, 'M001-SUMMARY.md'), '---\ntitle: Done\n---\nAll done.');
+
+      const state = await deriveState(base);
+      assertEq(state.phase, 'complete', 'all-summary-only: phase is complete');
+      assertEq(state.registry[0]?.status, 'complete', 'all-summary-only: M001 is complete');
+    } finally {
+      cleanup(base);
+    }
+  }
+
   // ═════════════════════════════════════════════════════════════════════════
   // Results
   // ═════════════════════════════════════════════════════════════════════════