From 6972d4c182237b9c6fd93cfc15bc52d4e606b53d Mon Sep 17 00:00:00 2001
From: Jinwoo-H <jinwoo0825@gmail.com>
Date: Sat, 12 Sep 2026 00:43:33 -0400
Subject: [PATCH] fix(relay): reuse canary across completed rollout batches

---
 ...cloud-deploy-relay-production-same-cap.yml |  2 +-
 .../relay-production-same-cap-wave.mjs        |  9 +++--
 .../relay-production-same-cap-wave.test.mjs   | 37 ++++++++++++++++++-
 3 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/.github/workflows/cloud-deploy-relay-production-same-cap.yml b/.github/workflows/cloud-deploy-relay-production-same-cap.yml
index 50d609b30d3..31fe9bfb203 100644
--- a/.github/workflows/cloud-deploy-relay-production-same-cap.yml
+++ b/.github/workflows/cloud-deploy-relay-production-same-cap.yml
@@ -62,7 +62,7 @@ on:
         required: false
         type: string
       canary-run-id:
-        description: Successful same-commit canary run required for batch-apply
+        description: Successful same-code canary in this rehome control generation; reusable across batches
         required: false
         type: string
       confirmation:
diff --git a/cloud/dev/scripts/relay-production-same-cap-wave.mjs b/cloud/dev/scripts/relay-production-same-cap-wave.mjs
index 6e84c1c9104..8caa68e7ff2 100644
--- a/cloud/dev/scripts/relay-production-same-cap-wave.mjs
+++ b/cloud/dev/scripts/relay-production-same-cap-wave.mjs
@@ -87,18 +87,21 @@ export function canaryAuthority(input) {
 }
 
 export function verifyCanaryAuthority(authority, expected, repositoryRoot) {
+  const selectorGeneration = Number(expected.selectorGeneration)
   if (
     authority?.v !== 1 ||
     !/^[0-9a-f]{40}$/.test(authority.commitSha ?? '') ||
     authority.runId !== expected.runId ||
     authority.targetDigest !== expected.targetDigest ||
     authority.rollbackDigest !== expected.rollbackDigest ||
-    authority.selectorGeneration !== Number(expected.selectorGeneration) ||
+    !Number.isSafeInteger(authority.selectorGeneration) ||
+    authority.selectorGeneration < 0 ||
+    !Number.isSafeInteger(selectorGeneration) ||
+    selectorGeneration < authority.selectorGeneration ||
     authority.rehomeGeneration !== Number(expected.rehomeGeneration) ||
     !SAME_CAP_CELLS.includes(authority.cellId)
   ) throw new Error('canary authority does not match this batch')
-  // The batch dispatch resolves main after the canary sealed, so bind to the same code, not the
-  // same SHA; every field above still pins this batch to that exact canary.
+  // Each cell checks exact live selector state; later batches may reuse this control epoch's canary.
   requireSameEvidenceCode({
     sealedSha: authority.commitSha,
     currentSha: expected.commitSha,
diff --git a/cloud/dev/scripts/relay-production-same-cap-wave.test.mjs b/cloud/dev/scripts/relay-production-same-cap-wave.test.mjs
index d636c324b33..7377f7a7af3 100644
--- a/cloud/dev/scripts/relay-production-same-cap-wave.test.mjs
+++ b/cloud/dev/scripts/relay-production-same-cap-wave.test.mjs
@@ -109,6 +109,41 @@ test('seals and verifies canary authority for later batches', () => {
   }), /does not match/)
 })
 
+test('reuses a canary across selector advances only within the same control epoch', () => {
+  const authority = canaryAuthority({
+    cellIds: 'production-gce-c7', targetDigest, rollbackDigest,
+    confirmation: `ROLL_RELAY_SAME_CAP ${targetDigest} production-gce-c7`,
+    commitSha: 'c'.repeat(40), runId: '42', selectorGeneration: '11', rehomeGeneration: '4'
+  })
+  const expected = {
+    commitSha: 'c'.repeat(40), runId: '42', targetDigest, rollbackDigest,
+    selectorGeneration: '21', rehomeGeneration: '4'
+  }
+  for (const generation of ['13', '14', '21', '29']) {
+    assert.equal(verifyCanaryAuthority(authority, {
+      ...expected, selectorGeneration: generation
+    }), authority)
+  }
+  for (const generation of ['12', '-1', 'NaN', 'Infinity', '13.5', '9007199254740992']) {
+    assert.throws(() => verifyCanaryAuthority(authority, {
+      ...expected, selectorGeneration: generation
+    }), /does not match/)
+  }
+  for (const generation of [-1, NaN, Infinity, 13.5, '13', Number.MAX_SAFE_INTEGER + 1]) {
+    assert.throws(() => verifyCanaryAuthority({
+      ...authority, selectorGeneration: generation
+    }, expected), /does not match/)
+  }
+  for (const mismatch of [
+    { rehomeGeneration: '3' }, { rehomeGeneration: '5' },
+    { targetDigest: rollbackDigest }, { rollbackDigest: targetDigest }, { runId: '43' }
+  ]) {
+    assert.throws(() => verifyCanaryAuthority(authority, {
+      ...expected, ...mismatch
+    }), /does not match/)
+  }
+})
+
 function gitIn(root, ...args) {
   return execFileSync('git', ['-C', root, ...args], { encoding: 'utf8' }).trim()
 }
@@ -158,7 +193,7 @@ test('a batch trusts a canary sealed by identical code at an ancestor commit', a
       runId: '42',
       targetDigest,
       rollbackDigest,
-      selectorGeneration: '13',
+      selectorGeneration: '21',
       rehomeGeneration: '4'
     }, repositoryRoot)
     assert.equal(verifyAt(repository.sameCode, repository.root).cellId, 'production-gce-c7')