fix(pr-daemon): defer session creation when maestro is unreachable

When maestro goes down, the daemon only sees aoe sessions. If a PR's
session lives in maestro, route() finds no match and creates a
duplicate on aoe. Track maestro health with exponential backoff and
suppress session creation until it answers again.

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

bin/reviewer-poll.ts

@@ -482,14 +482,26 @@ const MAESTRO_STATE: Record<string, string> = {
 // working -- so it degrades to an empty list. Logged once per outage, because
 // silently routing to half the sessions is exactly the failure this fixes.
 let maestroWarned = false;
+let maestroHealthy = true;
+let maestroBackoff = 10_000;
+let maestroNextRetry = 0;
+const MAESTRO_BACKOFF_MAX = 300_000;
+
 async function maestroRows(): Promise<any[]> {
+  if (Date.now() < maestroNextRetry) return [];
   try {
     const rows = JSON.parse(await maestro(["list", "--json"])).sessions ?? [];
     maestroWarned = false;
+    maestroHealthy = true;
+    maestroBackoff = 10_000;
+    maestroNextRetry = 0;
     return rows;
   } catch (e) {
     if (!maestroWarned) log(`maestro list failed, its sessions are invisible until it answers: ${e}`);
     maestroWarned = true;
+    maestroHealthy = false;
+    maestroNextRetry = Date.now() + maestroBackoff;
+    maestroBackoff = Math.min(maestroBackoff * 2, MAESTRO_BACKOFF_MAX);
     return [];
   }
 }
@@ -927,6 +939,12 @@ async function evaluate(prs: Pr[], mentioned: Set<string>, budget: { sessions: n
       const skill = role === "land" ? "land" : "review-pr";
 
       if (!session) {
+        // Maestro is unreachable: the session we cannot see may be the one
+        // that owns this branch. Defer creation until maestro answers again.
+        if (!maestroHealthy) {
+          log(`maestro unreachable, deferring ${full.key} (${role}) to avoid duplicates`);
+          continue;
+        }
         // Epoch gates session creation, not hint delivery: an old PR you want
         // covered gets covered by starting a session on its branch by hand.
         if (preEpoch && !mentioned.has(full.key)) continue;