From fe268efde13b2c54d4d91919a7a39c6c72a5064e Mon Sep 17 00:00:00 2001
From: Lily Shen <115414357+lilyshen0722@users.noreply.github.com>
Date: Fri, 30 Oct 2026 13:05:05 -0700
Subject: [PATCH] test(seats): a credential streamed one character per delta
 never reaches the record

Two cases beside the split tests, test-only (the store is unchanged):

- the whole value streamed one character per delta: every delta is held
  while it is still a prefix of the value, the completed value is replaced
  by the marker, and the joined message text is exactly the marker, written
  before run.settled;
- the value cut one character short, streamed one character per delta: the
  held tail is flushed as the marker before run.settled, and the joined text
  is exactly the marker.

Mutation check: with the hold-back disabled in store.js, both new tests fail.
The seats suite passes 247/247.

TASK-604

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Co-authored-by: wren <WyJ3cmVuIiwiZGVmYXVsdCJd@agents.commonly.invalid>
Agent-Model: claude/claude-haiku-5-5/max
---
 .../seats/test/record-redact-stream.test.js   | 28 +++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/packages/seats/test/record-redact-stream.test.js b/packages/seats/test/record-redact-stream.test.js
index 406a862f29..f783f228a0 100644
--- a/packages/seats/test/record-redact-stream.test.js
+++ b/packages/seats/test/record-redact-stream.test.js
@@ -115,6 +115,34 @@ test('two streams interleaved, each splitting the value, are scrubbed apart', ()
   }
 }));
 
+// One character per delta: each delta is a prefix of the value, so it is held
+// until the whole value has arrived (the marker) or the stream ends (the flush).
+test('a credential streamed one character per delta never reaches the record', () => withStore(async (store, root) => {
+  const runId = 'run-chars-full';
+  const run = store.startRun({ runId });
+  run.redact([CANARY]);
+  for (const ch of CANARY) run.emit('agent.message_chunk', { text: ch });
+  run.emit('run.settled', { outcome: 'ok', durationMs: 1, attempts: 1 });
+  assertScrubbed(store, root, runId, [{ kind: 'agent.message_chunk', expected: '[redacted]' }]);
+  const events = store.readRun(runId);
+  const settledAt = events.findIndex((e) => e.kind === 'run.settled');
+  const marker = events.findIndex((e) => e.kind === 'agent.message_chunk' && e.data.text === '[redacted]');
+  assert.ok(marker >= 0 && marker < settledAt, 'the marker landed before run.settled');
+}));
+
+test('a credential cut one character short, streamed one character per delta, flushes as the marker before settle', () => withStore(async (store, root) => {
+  const runId = 'run-chars-short-of-one';
+  const run = store.startRun({ runId });
+  run.redact([CANARY]);
+  for (const ch of CANARY.slice(0, -1)) run.emit('agent.message_chunk', { text: ch });
+  run.emit('run.settled', { outcome: 'failed', failure: { kind: 'exited', detail: 'gone' }, durationMs: 1, attempts: 1 });
+  assertScrubbed(store, root, runId, [{ kind: 'agent.message_chunk', expected: '[redacted]' }]);
+  const events = store.readRun(runId);
+  const settledAt = events.findIndex((e) => e.kind === 'run.settled');
+  const marker = events.findIndex((e) => e.kind === 'agent.message_chunk' && e.data.text === '[redacted]');
+  assert.ok(marker >= 0 && marker < settledAt, 'the held tail flushed before run.settled');
+}));
+
 test('a stream that ends mid-value writes the marker before settle, never the prefix', () => withStore(async (store, root) => {
   const run = store.startRun({ runId: 'run-held-settle' });
   run.redact([CANARY]);