diff --git a/scripts/lib/live-benchmark.mjs b/scripts/lib/live-benchmark.mjs
index a6302c7e8..33a47ad2e 100644
--- a/scripts/lib/live-benchmark.mjs
+++ b/scripts/lib/live-benchmark.mjs
@@ -148,17 +148,22 @@ export function buildInteractionRun(events, { iteration, scenario, goStartedAt,
 export function deriveJournalGenerationMetrics(snapshot = {}) {
   const timings = snapshot.generationTimings || {};
   const at = (phase) => Number(timings[phase]?.at);
-  const delta = (start, end) => (
-    Number.isFinite(at(start)) && Number.isFinite(at(end))
-      ? roundMs(Math.max(0, at(end) - at(start)))
-      : null
-  );
+  const timingErrors = [];
+  const delta = (start, end) => {
+    if (!Number.isFinite(at(start)) || !Number.isFinite(at(end))) return null;
+    if (at(end) < at(start)) {
+      timingErrors.push(`${end}_before_${start}`);
+      return null;
+    }
+    return roundMs(at(end) - at(start));
+  };
   return {
     workerPickupToSourceReadyMs: delta('picked_up', 'source_ready'),
     workerFirstGenerationToReviewableMs: delta('first_variant_generating', 'first_reviewable'),
     workerFirstValidationToReviewableMs: delta('first_variant_validating', 'first_reviewable'),
     workerRemainingGenerationToReadyMs: delta('remaining_variants_generating', 'all_variants_ready'),
     workerRemainingValidationToReadyMs: delta('remaining_variants_validating', 'all_variants_ready'),
+    journalTimingErrors: timingErrors,
     journalGenerationTimings: timings,
   };
 }
diff --git a/skill/scripts/live/codex-worker-supervisor.mjs b/skill/scripts/live/codex-worker-supervisor.mjs
index 4c1fe445e..336dca2d3 100644
--- a/skill/scripts/live/codex-worker-supervisor.mjs
+++ b/skill/scripts/live/codex-worker-supervisor.mjs
@@ -69,6 +69,7 @@ export class CodexLiveWorkerSupervisor {
     this.queue = Promise.resolve();
     this.active = null;
     this.canceled = new Set();
+    this.queuedGenerationIds = new Set();
     this.thread = null;
     this.model = null;
     this.liveSpec = '';
@@ -143,9 +144,12 @@ export class CodexLiveWorkerSupervisor {
         continue;
       }
       if (event.type === 'generate') {
+        if (this.queuedGenerationIds.has(event.id)) continue;
+        this.queuedGenerationIds.add(event.id);
         this.queue = this.queue
           .then(() => this.processGeneration(event))
-          .catch((error) => this.handleGenerationFailure(event, error));
+          .catch((error) => this.handleGenerationFailure(event, error))
+          .finally(() => this.queuedGenerationIds.delete(event.id));
         continue;
       }
       if (event.type === 'prefetch') continue;
diff --git a/tests/live-benchmark.test.mjs b/tests/live-benchmark.test.mjs
index bde33c5c4..116b397ac 100644
--- a/tests/live-benchmark.test.mjs
+++ b/tests/live-benchmark.test.mjs
@@ -30,6 +30,18 @@ describe('live benchmark metrics', () => {
     assert.equal(metrics.workerFirstValidationToReviewableMs, 30);
     assert.equal(metrics.workerRemainingGenerationToReadyMs, 185);
     assert.equal(metrics.workerRemainingValidationToReadyMs, 30);
+    assert.deepEqual(metrics.journalTimingErrors, []);
+  });
+
+  it('surfaces non-monotonic worker phases instead of reporting a false zero', () => {
+    const metrics = deriveJournalGenerationMetrics({
+      generationTimings: {
+        first_variant_generating: { at: 300 },
+        first_reviewable: { at: 200 },
+      },
+    });
+    assert.equal(metrics.workerFirstGenerationToReviewableMs, null);
+    assert.deepEqual(metrics.journalTimingErrors, ['first_reviewable_before_first_variant_generating']);
   });
 
   it('keeps published progressive CSS byte-stable and carries deferred params', () => {
diff --git a/tests/live-codex-worker-supervisor.test.mjs b/tests/live-codex-worker-supervisor.test.mjs
index eff3bff1b..46792a6a5 100644
--- a/tests/live-codex-worker-supervisor.test.mjs
+++ b/tests/live-codex-worker-supervisor.test.mjs
@@ -160,6 +160,31 @@ describe('Codex Live worker supervisor ownership and lifecycle', () => {
     }]);
   });
 
+  it('renews but never queues the same long-running generation twice', async () => {
+    const cwd = mkdtempSync(path.join(tmpdir(), 'codex-supervisor-duplicate-lease-'));
+    const client = fakeClient();
+    const supervisor = createSupervisor({
+      cwd,
+      statePath: path.join(cwd, 'state.json'),
+      client,
+    });
+    supervisor.thread = { id: 'live-worker-thread' };
+    let generations = 0;
+    supervisor.processGeneration = async () => {
+      generations += 1;
+      await new Promise((resolve) => setImmediate(resolve));
+    };
+    const events = [
+      { type: 'generate', id: 'generation-1', count: 3 },
+      { type: 'generate', id: 'generation-1', count: 3 },
+      { type: 'exit' },
+    ];
+    supervisor.fetchEvent = async () => events.shift();
+    await supervisor.run();
+    assert.equal(generations, 1);
+    assert.equal(supervisor.queuedGenerationIds.size, 0);
+  });
+
   it('reconnects and resumes the owned worker once after app-server loss', async () => {
     const cwd = mkdtempSync(path.join(tmpdir(), 'codex-supervisor-reconnect-'));
     const client = fakeClient();