test(idle): capture the stack behind each flush narration — the line alone cannot name its brain

The self-diagnosis from the last round worked: the box says this brain's own
providers were NOT called, so the flush pairs inside the 90 s window belong to
another brain in the same process. It could not say WHICH, and the advice it
gave — read the 'stdout | <file> > <test>' prefix — cannot work here: vitest
tags a stdout block with the test that is RUNNING, and these lines are captured
by this test's own console hook anyway. Teeing them through would only ever
print this test's name.

The call stack does name the driver, so it is captured beside each line and the
first one is reported: `kickBackgroundFlush('idle')` under `armIdleFlushTimer`
is some brain's cadence timer, the deferred-embed worker's commit path is a
brain still landing vectors, and a bare `flush()` is an explicit caller.

Why that distinction settles it. A flush only narrates PAST the dirty gate, and
`_dirtySinceLastFlush` is set in exactly three places — `noteWriteForPersistence()`
(both commit paths, and the deferred-embed worker lands its vectors through the
single-op one), `clear()`, and `repairIndex()`. So a narrating flush is a flush
whose brain really did commit a write; "0 ms" is the flush being cheap, not the
flush being empty. That reading rules OUT the re-arming-follow-up theory: the
queued follow-up is armed only by a concurrent flush() caller, cleared before
promotion, and a promoted run over a clean brain returns at the dirty gate
without touching a provider or printing a line.

Context the message now carries: the suite runs every file in ONE process, and
a create-versus-close scan puts 67 test files above the line — more brains made
than closed. This assertion is downstream of that, and the next red arrives with
the stack that names which one.

tests/integration/find-connected-order.test.ts

@@ -67,6 +67,13 @@ describe('find({ connected }) is graph-first: neighbours → filter → page', (
   })
 
   afterAll(async () => {
+    // CLOSE IT. Dropping the reference does not close a brain — it only makes
+    // it unreachable from here. The instance stays open and registered, its
+    // unref'd cadence timer keeps running, and because the gate config runs the
+    // whole suite in ONE process (pool: 'forks', singleFork: true) it goes on
+    // narrating its flushes into every test file that runs after this one.
+    // A test that leaks a brain is a defect of the test.
+    await brain?.close()
     brain = null as any
   })
 
@@ -137,13 +144,34 @@ describe('find({ connected }) is graph-first: neighbours → filter → page', (
   })
 
   it('walks the vector leg over the neighbours only', async () => {
+    // The SAME query without the vector leg, first. Both legs draw from the
+    // one neighbour set, so this is the control: it says whether a short answer
+    // came from the adjacency/filter (both legs short) or from the vector walk
+    // alone (only the vector leg short). Cheap, and it turns a bare count
+    // mismatch into a named half — this case has gone red on the gate box
+    // while passing in isolation and beside its own predecessor, so the next
+    // red must arrive already carrying the half it belongs to.
+    const control = await brain.find({
+      connected: { from: anchor, direction: 'out' },
+      where: { kind: 'note' },
+      limit: 5
+    })
+
     const results = await brain.find({
       vector: sharedVector,
       connected: { from: anchor, direction: 'out' },
       where: { kind: 'note' },
       limit: 5
     })
-    expect(results).toHaveLength(5)
+
+    expect(
+      results.length,
+      `the vector leg returned ${results.length} of a requested 5. The same query ` +
+        `WITHOUT the vector returned ${control.length}: if that is also short the ` +
+        `neighbour set or the filter is the cause, and if it is 5 the vector walk is — ` +
+        `note every row in this corpus carries an identical vector, so the walk is ` +
+        `ranking an exact tie.`
+    ).toBe(5)
     for (const r of results) expect(neighbourIds.has(r.entity.id)).toBe(true)
   })
 

tests/integration/idle-costs-nothing.test.ts

@@ -70,8 +70,22 @@ describe('an idle brain costs nothing', () => {
     await brain.flush()
 
     const logged: string[] = []
+    // The STACK behind each narration, kept beside the line it belongs to.
+    // vitest tags a stdout block with the test that is RUNNING, not the brain
+    // that wrote it, so teeing these lines through would only ever name this
+    // test. The call stack does name the driver: `kickBackgroundFlush('idle')`
+    // under `armIdleFlushTimer` is a cadence flush on some brain, the deferred-
+    // embed worker's commit path is a brain still landing vectors, and a bare
+    // `flush()` is an explicit caller. That distinction is the whole question.
+    const stacks: string[] = []
     const origLog = console.log
-    console.log = ((...a: unknown[]) => { logged.push(a.map(String).join(' ')) }) as typeof console.log
+    console.log = ((...a: unknown[]) => {
+      const line = a.map(String).join(' ')
+      logged.push(line)
+      if (/All indexes flushed to disk|Flushing Brainy indexes/.test(line)) {
+        stacks.push(new Error('flush narration').stack ?? '(no stack)')
+      }
+    }) as typeof console.log
 
     // Watch the providers directly: a flush that runs calls all of them.
     const storage = (brain as unknown as { storage: { flushCounts: () => Promise<void> } }).storage
@@ -113,10 +127,12 @@ describe('an idle brain costs nothing', () => {
     )
     expect(
       flushChatter,
-      `a flush narrated during the ${IDLE_WATCH_MS}ms idle window. This brain's own ` +
-        `providers were NOT called (asserted above), so the lines below were printed by ` +
-        `another brain alive in this process — find it by the 'stdout | <file> > <test>' ` +
-        `prefix in the run log:\n${flushChatter.join('\n')}`
+      `${flushChatter.length} flush line(s) narrated during the ${IDLE_WATCH_MS}ms idle ` +
+        `window. This brain's own providers were NOT called (asserted above), so another ` +
+        `brain alive in this process printed them — the suite runs every file in ONE ` +
+        `process and 67 test files create more brains than they close.\n` +
+        `${flushChatter.join('\n')}\n\n` +
+        `The stack behind the first one names the driver:\n${stacks[0] ?? '(none captured)'}`
     ).toEqual([])
   }, 180_000)