diff --git a/src/resources/extensions/gsd/state.ts b/src/resources/extensions/gsd/state.ts
index 5a3046c1b..58451ca1a 100644
--- a/src/resources/extensions/gsd/state.ts
+++ b/src/resources/extensions/gsd/state.ts
@@ -126,7 +126,12 @@ export async function getActiveMilestoneId(basePath: string): Promise<string | n
       // A draft milestone is still "active" — this function only determines which milestone is current.
     }
     const roadmap = parseRoadmap(content);
-    if (!isMilestoneComplete(roadmap)) return mid;
+    if (!isMilestoneComplete(roadmap)) {
+      // Summary is the terminal artifact — if it exists, the milestone is
+      // complete even when roadmap checkboxes weren't ticked (#864).
+      const summaryFile = resolveMilestoneFile(basePath, mid, "SUMMARY");
+      if (!summaryFile) return mid;
+    }
   }
   return null;
 }
@@ -258,7 +263,13 @@ async function _deriveStateImpl(basePath: string): Promise<GSDState> {
     }
     const rmap = parseRoadmap(rc);
     roadmapCache.set(mid, rmap);
-    if (!isMilestoneComplete(rmap)) continue;
+    if (!isMilestoneComplete(rmap)) {
+      // Summary is the terminal artifact — if it exists, the milestone is
+      // complete even when roadmap checkboxes weren't ticked (#864).
+      const sf = resolveMilestoneFile(basePath, mid, "SUMMARY");
+      if (sf) completeMilestoneIds.add(mid);
+      continue;
+    }
     const sf = resolveMilestoneFile(basePath, mid, "SUMMARY");
     if (sf) completeMilestoneIds.add(mid);
   }
@@ -357,26 +368,33 @@ async function _deriveStateImpl(basePath: string): Promise<GSDState> {
       } else {
         registry.push({ id: mid, title, status: 'complete' });
       }
-    } else if (!activeMilestoneFound) {
-      // Check milestone-level dependencies before promoting to active
-      const contextFile = resolveMilestoneFile(basePath, mid, "CONTEXT");
-      const contextContent = contextFile ? await cachedLoadFile(contextFile) : null;
-      const deps = parseContextDependsOn(contextContent);
-      const depsUnmet = deps.some(dep => !completeMilestoneIds.has(dep));
-      if (depsUnmet) {
-        registry.push({ id: mid, title, status: 'pending', dependsOn: deps });
-        // Do NOT set activeMilestoneFound — let the loop continue to the next milestone
-      } else {
-        activeMilestone = { id: mid, title };
-        activeRoadmap = roadmap;
-        activeMilestoneFound = true;
-        registry.push({ id: mid, title, status: 'active', ...(deps.length > 0 ? { dependsOn: deps } : {}) });
-      }
     } else {
-      const contextFile2 = resolveMilestoneFile(basePath, mid, "CONTEXT");
-      const contextContent2 = contextFile2 ? await cachedLoadFile(contextFile2) : null;
-      const deps2 = parseContextDependsOn(contextContent2);
-      registry.push({ id: mid, title, status: 'pending', ...(deps2.length > 0 ? { dependsOn: deps2 } : {}) });
+      // Roadmap slices not all checked — but if a summary exists, the milestone
+      // is still complete. The summary is the terminal artifact (#864).
+      const summaryFile = resolveMilestoneFile(basePath, mid, "SUMMARY");
+      if (summaryFile) {
+        registry.push({ id: mid, title, status: 'complete' });
+      } else if (!activeMilestoneFound) {
+        // Check milestone-level dependencies before promoting to active
+        const contextFile = resolveMilestoneFile(basePath, mid, "CONTEXT");
+        const contextContent = contextFile ? await cachedLoadFile(contextFile) : null;
+        const deps = parseContextDependsOn(contextContent);
+        const depsUnmet = deps.some(dep => !completeMilestoneIds.has(dep));
+        if (depsUnmet) {
+          registry.push({ id: mid, title, status: 'pending', dependsOn: deps });
+          // Do NOT set activeMilestoneFound — let the loop continue to the next milestone
+        } else {
+          activeMilestone = { id: mid, title };
+          activeRoadmap = roadmap;
+          activeMilestoneFound = true;
+          registry.push({ id: mid, title, status: 'active', ...(deps.length > 0 ? { dependsOn: deps } : {}) });
+        }
+      } else {
+        const contextFile2 = resolveMilestoneFile(basePath, mid, "CONTEXT");
+        const contextContent2 = contextFile2 ? await cachedLoadFile(contextFile2) : null;
+        const deps2 = parseContextDependsOn(contextContent2);
+        registry.push({ id: mid, title, status: 'pending', ...(deps2.length > 0 ? { dependsOn: deps2 } : {}) });
+      }
     }
   }
 
diff --git a/src/resources/extensions/gsd/tests/derive-state.test.ts b/src/resources/extensions/gsd/tests/derive-state.test.ts
index 08fc0f347..53fbe61c9 100644
--- a/src/resources/extensions/gsd/tests/derive-state.test.ts
+++ b/src/resources/extensions/gsd/tests/derive-state.test.ts
@@ -779,6 +779,49 @@ slice: S01
     }
   }
 
+  // ─── Test: unchecked roadmap slices + summary → complete (summary is terminal) ────
+  console.log('\n=== unchecked roadmap slices + summary → complete (summary is terminal) ===');
+  {
+    const base = createFixtureBase();
+    try {
+      // M001: roadmap has unchecked slices but a summary exists — should be complete
+      writeRoadmap(base, 'M001', `# M001: First Milestone\n\n**Vision:** Already done.\n\n## Slices\n\n- [ ] **S01: Unchecked slice** \`risk:low\` \`depends:[]\`\n  > Work was done but checkbox never ticked.\n- [ ] **S02: Another unchecked** \`risk:low\` \`depends:[]\`\n  > Same.\n`);
+      writeMilestoneSummary(base, 'M001', '---\nid: M001\n---\n\n# M001: First Milestone\n\n**Completed despite unchecked roadmap.**');
+      // M002: genuinely incomplete — should be the active milestone
+      writeRoadmap(base, 'M002', `# M002: Active Milestone\n\n**Vision:** Do stuff.\n\n## Slices\n\n- [ ] **S01: Work slice** \`risk:low\` \`depends:[]\`\n  > Needs work.\n`);
+
+      const state = await deriveState(base);
+      const m001Entry = state.registry.find(e => e.id === 'M001');
+      assertEq(m001Entry?.status, 'complete', 'M001 with unchecked roadmap + summary is complete');
+      assertEq(state.activeMilestone?.id, 'M002', 'active milestone is M002, not M001');
+    } finally {
+      cleanup(base);
+    }
+  }
+
+  // ─── Test: unchecked roadmap + summary counts toward completeMilestoneIds (deps) ────
+  console.log('\n=== unchecked roadmap + summary satisfies dependency ===');
+  {
+    const base = createFixtureBase();
+    try {
+      // M001: unchecked roadmap + summary → complete
+      writeRoadmap(base, 'M001', `# M001: Foundation\n\n**Vision:** Done.\n\n## Slices\n\n- [ ] **S01: Setup** \`risk:low\` \`depends:[]\`\n  > Done.\n`);
+      writeMilestoneSummary(base, 'M001', '---\nid: M001\n---\n\n# M001: Foundation\n\n**Done.**');
+      // M002: depends on M001 — should be active since M001 is complete
+      writeRoadmap(base, 'M002', `# M002: Dependent\n\n**Vision:** Depends on M001.\n\n## Slices\n\n- [ ] **S01: Work** \`risk:low\` \`depends:[]\`\n  > Work.\n`);
+      const contextDir = join(base, '.gsd', 'milestones', 'M002');
+      mkdirSync(contextDir, { recursive: true });
+      writeFileSync(join(contextDir, 'M002-CONTEXT.md'), '---\ndepends_on:\n  - M001\n---\n\n# M002 Context\n\nDepends on M001.');
+
+      const state = await deriveState(base);
+      assertEq(state.activeMilestone?.id, 'M002', 'M002 is active — M001 dependency satisfied via summary');
+      const m002Entry = state.registry.find(e => e.id === 'M002');
+      assertEq(m002Entry?.status, 'active', 'M002 status is active, not pending');
+    } finally {
+      cleanup(base);
+    }
+  }
+
   report();
 }