fix: exponential idle backoff for the analysis worker

The analysis worker's flat 1s idle sleep meant an empty queue fired a lease query
per worker per second forever (audit). Add idle_backoff (1s..30s, reset on lease),
mirroring the crawler. Unit-tested.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/Cargo.lock

@@ -1558,7 +1558,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.128.20"
+version = "0.128.21"
 dependencies = [
  "anyhow",
  "argon2",

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.128.20"
+version = "0.128.21"
 edition = "2021"
 default-run = "mangalord"
 

backend/src/analysis/daemon.rs

@@ -37,6 +37,22 @@ const LEASE_HEARTBEAT: Duration = Duration::from_secs(20);
 /// long enough not to hammer `/health` while vision is down.
 const READINESS_POLL: Duration = Duration::from_secs(2);
 
+/// Longest an idle analysis worker waits between lease polls, bounding the
+/// exponential [`idle_backoff`].
+const IDLE_BACKOFF_CAP: Duration = Duration::from_secs(30);
+
+/// Exponential idle backoff (1s, 2s, 4s … capped at [`IDLE_BACKOFF_CAP`]).
+/// `consecutive_empty` is the number of empty lease polls so far (0 on the first
+/// miss); reset to 0 the moment a job is leased. Replaces the old flat 1s sleep
+/// so an idle worker isn't firing a `SELECT … FOR UPDATE SKIP LOCKED` lease
+/// query every second (audit: analysis daemon idle poll). Mirrors the crawler
+/// daemon's backoff.
+fn idle_backoff(consecutive_empty: u32) -> Duration {
+    let cap = IDLE_BACKOFF_CAP.as_secs();
+    let secs = 1u64.checked_shl(consecutive_empty).unwrap_or(cap).min(cap);
+    Duration::from_secs(secs)
+}
+
 /// The unit of work: analyze one page. Implemented by
 /// [`RealAnalyzeDispatcher`] in production and stubbed in tests.
 #[async_trait]
@@ -135,6 +151,9 @@ impl WorkerContext {
         // Last observed readiness, so we log only on transitions (not every
         // poll). `None` until the first probe.
         let mut was_ready: Option<bool> = None;
+        // Empty lease polls seen in a row, driving the idle backoff. Reset to 0
+        // the moment a job is leased.
+        let mut consecutive_empty: u32 = 0;
         loop {
             if self.cancel.is_cancelled() {
                 tracing::info!(worker = self.id, "analysis worker: shutdown");
@@ -178,11 +197,15 @@ impl WorkerContext {
                     }
                 };
             let Some(lease) = leases.into_iter().next() else {
-                if self.sleep_or_cancel(Duration::from_secs(1)).await {
+                let wait = idle_backoff(consecutive_empty);
+                consecutive_empty = consecutive_empty.saturating_add(1);
+                if self.sleep_or_cancel(wait).await {
                     return;
                 }
                 continue;
             };
+            // Leased work — drop back to a tight poll cadence.
+            consecutive_empty = 0;
             self.process_lease(lease).await;
         }
     }
@@ -510,6 +533,17 @@ mod tests {
     use tokio::io::{AsyncReadExt, AsyncWriteExt};
     use tokio::net::TcpListener;
 
+    #[test]
+    fn idle_backoff_grows_exponentially_and_caps() {
+        assert_eq!(idle_backoff(0), Duration::from_secs(1));
+        assert_eq!(idle_backoff(1), Duration::from_secs(2));
+        assert_eq!(idle_backoff(2), Duration::from_secs(4));
+        assert_eq!(idle_backoff(4), Duration::from_secs(16));
+        // Caps at IDLE_BACKOFF_CAP (30s) and never overflows on large counts.
+        assert_eq!(idle_backoff(5), IDLE_BACKOFF_CAP);
+        assert_eq!(idle_backoff(100), IDLE_BACKOFF_CAP);
+    }
+
     /// Bind an ephemeral port that answers every request with `status_line`
     /// (e.g. `"200 OK"`), and return its `/health` URL. The probe under test
     /// only inspects the status code, so a zero-length body is enough.

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.128.20",
+  "version": "0.128.21",
   "private": true,
   "type": "module",
   "scripts": {