From db89ced0f502c282ad70e7d6e63659bf8eac1b36 Mon Sep 17 00:00:00 2001
From: Jinwoo Hong <73622457+Jinwoo-H@users.noreply.github.com>
Date: Mon, 19 Oct 2026 22:36:42 -0400
Subject: [PATCH] fix(relay-ops): stop the reserve watch cleanly when the cell
 leaves reserve (#30972)

evaluateWatchSample's two early returns (waiting for reserve to apply, and
a cell flipped back to db by hand) carried no pages, so watchSegment threw
'result.pages is not iterable' and the run ended as failed instead of
stopped (c29, 10-20 02:25Z, run 39354895994).
---
 .../dev/scripts/relay-reserve-watch-rules.mjs |  4 +--
 .../scripts/watch-relay-reserve-cell.test.mjs | 27 +++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/cloud/dev/scripts/relay-reserve-watch-rules.mjs b/cloud/dev/scripts/relay-reserve-watch-rules.mjs
index 5ade25766ad..9da9d1ce40b 100644
--- a/cloud/dev/scripts/relay-reserve-watch-rules.mjs
+++ b/cloud/dev/scripts/relay-reserve-watch-rules.mjs
@@ -360,14 +360,14 @@ export function evaluateWatchSample(state, sample, { unverifiableLimit }) {
     if (!seen && at < state.startedAt + RESERVE_WATCH_RULES.reserveApplyWaitMs) {
       // Not judged, and the streak holds: the reserve write may not have applied yet.
       const rules = { reserve: pending(`switch file says ${cell.admitModeConfigured}; waiting for reserve to apply`) }
-      return { state: next, rules, line: sampleLine(next, sample, rules) }
+      return { state: next, rules, line: sampleLine(next, sample, rules), pages: [] }
     }
     // Someone else flipped it back (or it never became reserve): nothing left to watch.
     next.state = seen ? 'stopped' : 'refused'
     next.verdict = seen
       ? `${state.cellId} is not in reserve mode (switch file says ${cell.admitModeConfigured})`
       : `${state.cellId} did not report reserve mode within ${RESERVE_WATCH_RULES.reserveApplyWaitMs / MINUTE_MS} min (switch file says ${cell.admitModeConfigured})`
-    return { state: next, rules: {}, line: sampleLine(next, sample, {}) }
+    return { state: next, rules: {}, line: sampleLine(next, sample, {}), pages: [] }
   }
   if (cell.ok) {
     next.reserveSeenAt = state.reserveSeenAt ?? at
diff --git a/cloud/dev/scripts/watch-relay-reserve-cell.test.mjs b/cloud/dev/scripts/watch-relay-reserve-cell.test.mjs
index 98c9829f8fa..0f5b1467c0c 100644
--- a/cloud/dev/scripts/watch-relay-reserve-cell.test.mjs
+++ b/cloud/dev/scripts/watch-relay-reserve-cell.test.mjs
@@ -788,6 +788,33 @@ test('a quiet fleet with zero director 503s watches on and never trips', async (
   }
 })
 
+// 10-20 c29: a hand flip back to db mid-watch crashed the segment ("result.pages is not iterable").
+test('a segment that waits for reserve, then sees a hand flip back to db, stops without crashing', async () => {
+  const directory = await mkdtemp(join(tmpdir(), 'relay-reserve-watch-'))
+  try {
+    let clock = START
+    const config = parseAt(
+      watchValues({ 'state-file': join(directory, 'state.json'), 'segment-minutes': '10', 'flipped-at': new Date(START - 2 * MINUTE).toISOString() })
+    )
+    const db = { flagsApplied: { generation: 5, flags: { admitMode: 'db', readinessLocal: true } }, admitModeEffective: 'db' }
+    const lines = []
+    const state = await watchSegment(config, {
+      ...fakeSources({ cell: (sample) => (sample === 1 || sample >= 4 ? db : {}) }),
+      idToken: 'id',
+      retryDelayMs: 0,
+      now: () => clock,
+      sleep: async (ms) => { clock += ms },
+      log: (line) => lines.push(JSON.parse(line))
+    })
+    assert.equal(lines[0].rules.reserve.status, 'pending')
+    assert.equal(state.state, 'stopped')
+    assert.match(state.verdict, /is not in reserve mode \(switch file says db\)/)
+    assert.equal(lines.length, 4)
+  } finally {
+    await rm(directory, { recursive: true, force: true })
+  }
+})
+
 // 2026-10-18's false trips: 503s tripled with traffic, nearly all a host re-dialling early.
 const rateLimited = (perLine) => ({ placementRejectionsByReasonDelta: { 'host-rate-limited': perLine }, assign503sByCauseDelta: { 'placement-lane': perLine } })