fix(auto): clear parse cache in dispatch + verify completion in handleAgentEnd

Kills two independent failure paths causing the recurring dispatch loop bug:

Path B: dispatchNextUnit() called clearPathCache() but not clearParseCache(),
allowing stale parsed roadmap data (with [ ] instead of [x]) to persist
through the doctor→dispatch transition.

Path A: handleAgentEnd() never verified whether the just-completed unit
produced its expected artifact before re-entering the dispatch loop.
Now persists completion key after verification, so the idempotency
check in dispatchNextUnit() skips already-completed units.

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

src/resources/extensions/gsd/auto.ts

@@ -836,6 +836,24 @@ export async function handleAgentEnd(
     } catch {
       // Non-fatal
     }
+
+    // ── Path A fix: verify artifact and persist completion before re-entering dispatch ──
+    // After doctor + rebuildState, check whether the just-completed unit actually
+    // produced its expected artifact. If so, persist the completion key now so the
+    // idempotency check at the top of dispatchNextUnit() skips it — even if
+    // deriveState() still returns this unit as active (e.g. branch mismatch).
+    try {
+      if (verifyExpectedArtifact(currentUnit.type, currentUnit.id, basePath)) {
+        const completionKey = `${currentUnit.type}/${currentUnit.id}`;
+        if (!completedKeySet.has(completionKey)) {
+          persistCompletedKey(basePath, completionKey);
+          completedKeySet.add(completionKey);
+        }
+        invalidateStateCache();
+      }
+    } catch {
+      // Non-fatal — worst case we fall through to normal dispatch which has its own checks
+    }
   }
 
   // ── Post-unit hooks: check if a configured hook should run before normal dispatch ──
@@ -1391,6 +1409,9 @@ async function dispatchNextUnit(
 
   // Clear stale directory listing cache so deriveState sees fresh disk state (#431)
   clearPathCache();
+  // Clear parsed roadmap/plan cache — doctor may have re-populated it with
+  // stale data between handleAgentEnd and this dispatch call (Path B fix).
+  clearParseCache();
 
   let state = await deriveState(basePath);
   let mid = state.activeMilestone?.id;