feat(clustering): 1h TTL + skip recompute when tasks unchanged

focus-area now recomputes at most once per hour, and only if the task list
actually changed since the last compute.

- focus-area TTL: 43200s → 3600s; version bumped to 2.1.0
- computeAndStore hashes sorted task contents (MD5) and checks the stored
  _task_hash in the existing snapshot; skips the ml-serving call when the
  hash matches and the output isn't expired
- ml-serving injects _task_hash into the snapshot so the next cycle can compare

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/api/src/routes/agent-outputs.ts

@@ -155,6 +155,31 @@ async function persistInferredPrefs(
   }
 }
 
+function taskListHash(tasks: { content?: string }[]): string {
+  const sorted = tasks
+    .map((t) => t.content?.trim() ?? '')
+    .filter(Boolean)
+    .sort()
+    .join('\n');
+  return crypto.createHash('md5').update(sorted).digest('hex');
+}
+
+async function isUpToDate(userId: string, agentId: string, currentHash: string): Promise<boolean> {
+  const now = new Date().toISOString();
+  const rows = await db
+    .select({ signalsSnapshot: agentOutputs.signalsSnapshot, expiresAt: agentOutputs.expiresAt })
+    .from(agentOutputs)
+    .where(and(eq(agentOutputs.userId, userId), eq(agentOutputs.agentId, agentId)))
+    .limit(1);
+  if (!rows.length) return false;
+  const row = rows[0];
+  if (row.expiresAt <= now) return false;
+  try {
+    const snapshot = JSON.parse(row.signalsSnapshot ?? '{}') as { _task_hash?: string };
+    return snapshot._task_hash === currentHash;
+  } catch { return false; }
+}
+
 export async function computeAndStore(userId: string, agentId: string): Promise<void> {
   let tasks: object[] = [];
   try {
@@ -176,6 +201,9 @@ export async function computeAndStore(userId: string, agentId: string): Promise<
     // No integration or fetch error — agents that need tasks will report "no tasks"
   }
 
+  const currentTaskHash = taskListHash(tasks as { content?: string }[]);
+  if (await isUpToDate(userId, agentId, currentTaskHash)) return;
+
   let profile: Profile = {};
   try {
     profile = await getProfile(userId);
@@ -202,7 +230,7 @@ export async function computeAndStore(userId: string, agentId: string): Promise<
   const mlResp = await fetch(`${config.ML_SERVING_URL}/agents/${agentId}/compute`, {
     method: 'POST',
     headers: { 'Content-Type': 'application/json' },
-    body: JSON.stringify({ user_id: userId, tasks, profile, feedback_history: feedbackHistory, agent_prefs: agentPrefs, enrichment_cache: enrichmentCache }),
+    body: JSON.stringify({ user_id: userId, tasks, profile, feedback_history: feedbackHistory, agent_prefs: agentPrefs, enrichment_cache: enrichmentCache, task_hash: currentTaskHash }),
     signal: AbortSignal.timeout(60_000),
   });