src/brainy.ts

@@ -767,34 +767,6 @@ export class Brainy<T = any> implements BrainyInterface<T> {
   private _persistIdleTimer: ReturnType<typeof setTimeout> | null = null
   private _persistBackgroundFlight: Promise<void> | null = null
 
-  /**
-   * FLUSH IS SINGLE-FLIGHT, AND THE QUEUE IS ONE DEEP. `_flushInFlight` is the
-   * flush body actually running; `_flushFollowUp` is the AT MOST ONE flush
-   * queued behind it. Every caller — the write cadence, the cross-process
-   * flush-request watcher, an application calling `flush()` directly — either
-   * runs (nothing in flight), or joins the single queued follow-up.
-   *
-   * WHY A FOLLOW-UP RATHER THAN JOINING THE RUNNING FLUSH: a caller flushes to
-   * make ITS writes durable, and those writes may have landed after the
-   * running flush read its state. Joining would return "flushed" over data
-   * that was never persisted. Chaining one follow-up costs nothing when there
-   * is nothing new (a clean brain's flush returns immediately — see
-   * `_dirtySinceLastFlush`) and is correct when there is.
-   *
-   * MEASURED, in the production shutdown this was written for: two
-   * "Flushing Brainy indexes and caches to disk..." runs overlapping 3s
-   * apart on one brain, their walls growing 295ms → 4.9s as they contended
-   * for the same providers.
-   */
-  private _flushInFlight: Promise<void> | null = null
-  private _flushFollowUp: Promise<void> | null = null
-  /** Flush bodies that got past the single-flight gate (pinned by tests). */
-  private _flushBodyRuns = 0
-  /** Flush bodies running right now, and the high-water mark — which the
-   *  single-flight law requires to stay at 1 (pinned by tests). */
-  private _flushBodiesActive = 0
-  private _flushConcurrencyPeak = 0
-
   // DEFERRED EMBEDDING (MT5): pending markers are LOG RECORDS — an
   // embed.pending record rides the deferred write's own commit fact and
   // embed.landed rides the landing commit; this set is the in-memory
@@ -917,24 +889,6 @@ export class Brainy<T = any> implements BrainyInterface<T> {
   // applies only to instances that were never closed.
   private closed = false
 
-  /**
-   * THE ONE CLOSE. Set SYNCHRONOUSLY by the first `close()` call, before that
-   * call yields, and never cleared — close is terminal. Every later or
-   * concurrent caller receives this same promise, so a shutdown with two
-   * callers (a host's pool close and the engine's own signal handler) runs
-   * ONE teardown, not two.
-   *
-   * MEASURED, the day this was added: a host that owns shutdown called
-   * `close()` on every pooled store at SIGTERM while the engine's signal
-   * handler flushed the same instances in parallel and released their writer
-   * locks in its own `finally`. One store took 149s to close (148s of it
-   * silent) against 24s for its idle siblings, and the same race in a local
-   * reproduction printed `Writer fence lost … the lock file is gone` — the
-   * handler observing a lock the close it was racing had already released.
-   * Two owners of one shutdown; now there is one, whoever calls first.
-   */
-  private _closeInFlight: Promise<void> | null = null
-
   // Index-build-at-open state. `lazyRebuildCompleted` predates the health-gate
   // law (it named a first-QUERY lazy rebuild) and stays for `getIndexStatus()`
   // API compatibility, but its truth changed: a needed rebuild now runs
@@ -2122,88 +2076,105 @@ export class Brainy<T = any> implements BrainyInterface<T> {
    */
   private registerShutdownHooks(): void {
     /**
-     * The signal-path shutdown. ONE OWNER PER BRAIN, AND THE PATH IS `close()`.
+     * The signal-path shutdown. THREE LAWS, each written by a production
+     * shutdown that looked clean and wasn't:
      *
-     * WHAT THIS REPLACED, and why. The handler used to run its own shutdown —
-     * a parallel per-component flush, the generation store's close, a second
-     * parallel round of component closes, and a `finally` that stopped the
-     * flush-request watcher and released the writer lock. That is a SECOND
-     * teardown of the same brain, and a host application with its own SIGTERM
-     * handler (the shape every pooled deployment has) ran the FIRST one at the
-     * same moment. MEASURED in production the day this changed: a host closing
-     * seven pooled stores at SIGTERM printed "Shutdown signal received -
-     * flushing pending data...", went silent for 148s, printed "Flushed
-     * successfully (1 instance)", and the host's own close of that same store
-     * returned 1s later — 149s, against 24s for the six stores with no engine
-     * work in flight. The same race reproduced locally as
-     * `Failed to flush one Brainy instance on shutdown: Writer fence lost …
-     * the lock file is gone`: this handler observing a lock that the close it
-     * was racing had already released.
-     *
-     * SO: defer one macrotask, then per instance either STEP ASIDE (a close
-     * has begun or finished — its owner owns the flush, the markers and the
-     * lock) or `await instance.close()` — the one durable path, identical to
-     * what any caller gets. The three laws the old block carried are all
-     * satisfied by `close()`, each verified against its code:
-     *
-     * 1. PER-INSTANCE ISOLATION — kept HERE, in the per-instance try/catch
-     *    below: one brain's failed close never aborts the loop over the rest.
-     *    (`close()` itself is per-instance by construction.)
-     * 2. THE MARKER IS PART OF SHUTDOWN — `close()` → `closeDurableSteps()`
-     *    Phase 1 awaits `this.generationStore.close()`, which persists the
-     *    counter, advances the fold checkpoint and stamps the clean-shutdown
-     *    marker LAST. That is the step that decides adopt-vs-fold at the next
-     *    open, and it is the same call the old block made.
-     * 3. THE LOCK IS ALWAYS GIVEN UP — `close()`'s terminal releases run
-     *    whether the durable steps threw or not (its contract: "TWO PARTS, AND
-     *    THE SECOND IS UNCONDITIONAL"): `stopFlushRequestWatcher()` then
-     *    `releaseWriterLock()`, then the VFS shutdown and the terminal
-     *    `closed` flag, and only then is the original failure rethrown.
-     *    `close()` releases the lock in MORE cases than the old block did — it
-     *    also drains the metadata write buffer first, so no pending write can
-     *    land after a successor writer claims the lock.
+     * 1. PER-INSTANCE ISOLATION. This used to be one `try` around a loop over
+     *    every open brain: the first instance whose flush rejected aborted the
+     *    loop, so every remaining brain kept its writer lock and its unwritten
+     *    markers — and the process still exited 0. A pool of brains failed in
+     *    a batch, not one at a time.
+     * 2. THE MARKER IS PART OF SHUTDOWN. Flushing the indexes without closing
+     *    the generation store leaves the clean-shutdown marker unwritten, so
+     *    the NEXT open reads the store as crashed and folds the whole
+     *    generation log — measured in tens of seconds on a real store, paid on
+     *    every restart, after a shutdown the operator saw exit 0.
+     * 3. THE LOCK IS ALWAYS GIVEN UP. In a `finally`, per instance: a process
+     *    on its way out holds nothing.
      */
-    const closeOnShutdown = async () => {
+    const flushOnShutdown = async () => {
       console.log('Shutdown signal received - flushing pending data...')
-      // DEFER ONE MACROTASK. A host application registers its own listener on
-      // the same signal, and Node runs listeners in registration order — ours
-      // is usually first, because the brain was opened before the host wired
-      // its shutdown. Yielding once lets every other listener for this signal
-      // run its synchronous prologue, so a host that calls close() gets to be
-      // the owner. It is only a courtesy, never the safety: close()'s own
-      // single-flight gate is what makes a lost race harmless.
-      await new Promise<void>((resolve) => setImmediate(resolve))
-
-      let closedCount = 0
-      let deferredCount = 0
+      let flushedCount = 0
       let failedCount = 0
       // Snapshot: close() splices Brainy.instances while we iterate.
       for (const instance of [...Brainy.instances]) {
         if (!instance.initialized) continue
-        // SOMEONE ELSE OWNS THIS ONE. Not a flush, not a lock release, not a
-        // component close — nothing. Touching a brain whose close is running
-        // is the whole defect this handler was rewritten for.
-        if (instance.closed || instance._closeInFlight !== null) {
-          deferredCount++
-          continue
-        }
         try {
-          // Law 1: this try/catch is the isolation — the loop continues.
-          await instance.close()
-          closedCount++
+          // Flush all buffered data (parallel across components, this brain only).
+          await Promise.all([
+            (async () => {
+              if (instance.storage && typeof instance.storage.flushCounts === 'function') {
+                await instance.storage.flushCounts()
+              }
+            })(),
+            (async () => {
+              if (instance.metadataIndex && typeof instance.metadataIndex.flush === 'function') {
+                await instance.metadataIndex.flush()
+              }
+            })(),
+            (async () => {
+              if (instance.graphIndex && typeof instance.graphIndex.flush === 'function') {
+                await instance.graphIndex.flush()
+              }
+            })(),
+            (async () => {
+              if (instance.index && typeof instance.index.flush === 'function') {
+                await instance.index.flush()
+              }
+            })()
+          ])
+
+          // Close the generation store: persists the counter, advances the
+          // fold checkpoint, and stamps the clean-shutdown marker LAST — the
+          // one step that decides whether the next open adopts or folds. Law 2.
+          if (instance.generationStore && !instance.isReadOnly) {
+            await instance.generationStore.close()
+          }
+
+          // Close components to stop timers that would prevent clean process exit
+          await Promise.all([
+            (async () => {
+              if (instance.graphIndex && typeof instance.graphIndex.close === 'function') {
+                await instance.graphIndex.close()
+              }
+            })(),
+            (async () => {
+              const index = instance.index as JsHnswVectorIndex & VectorIndexOptionalHooks
+              if (index && typeof index.close === 'function') {
+                await index.close()
+              }
+            })(),
+            (async () => {
+              const metadataIndex = instance.metadataIndex as MetadataIndexManager & MetadataIndexOptionalHooks
+              if (metadataIndex && typeof metadataIndex.close === 'function') {
+                await metadataIndex.close()
+              }
+            })()
+          ])
+          flushedCount++
         } catch (error) {
           failedCount++
-          console.error('Failed to close one Brainy instance on shutdown:', error)
+          console.error('Failed to flush one Brainy instance on shutdown:', error)
+        } finally {
+          // Law 3 — the lock and the watcher go regardless.
+          try {
+            if (instance.storage && typeof instance.storage.stopFlushRequestWatcher === 'function') {
+              instance.storage.stopFlushRequestWatcher()
+            }
+          } catch (error) {
+            console.error('Failed to stop the flush-request watcher on shutdown:', error)
+          }
+          try {
+            if (instance.storage && typeof instance.storage.releaseWriterLock === 'function') {
+              await instance.storage.releaseWriterLock()
+            }
+          } catch (error) {
+            console.error('Failed to release the writer lock on shutdown:', error)
+          }
         }
       }
-      if (closedCount > 0) {
-        console.log(`Flushed successfully (${closedCount} instance${closedCount > 1 ? 's' : ''})`)
-      }
-      if (deferredCount > 0) {
-        console.log(
-          `${deferredCount} Brainy instance${deferredCount > 1 ? 's are' : ' is'} already ` +
-            `closing — left to the caller that owns that close.`
-        )
+      if (flushedCount > 0) {
+        console.log(`Flushed successfully (${flushedCount} instance${flushedCount > 1 ? 's' : ''})`)
       }
       if (failedCount > 0) {
         console.error(
@@ -2230,29 +2201,19 @@ export class Brainy<T = any> implements BrainyInterface<T> {
      * markers unwritten. When the host has its own handler (listener count
      * above our own), the host owns the exit; Brainy only makes its data
      * durable and steps aside.
-     *
-     * THE COUNT IS TAKEN WHEN THE SIGNAL ARRIVES, not after the shutdown ran.
-     * "Is anyone else handling this signal?" is a question about the moment
-     * the signal landed. Asking afterwards reads a process that has already
-     * torn itself down: the handler now CLOSES its instances, and closing the
-     * last brain deregisters Brainy's own listeners — so a host application's
-     * single remaining listener would look like `<= 1` and get force-exited
-     * out of its own graceful shutdown, precisely the failure above.
      */
-    const exitIfSoleShutdownOwner = (ownersWhenSignalled: number): void => {
-      if (ownersWhenSignalled <= 1) {
+    const exitIfSoleShutdownOwner = (signal: 'SIGTERM' | 'SIGINT'): void => {
+      if (process.listenerCount(signal) <= 1) {
         process.exit(0)
       }
     }
     Brainy.sigtermListener = async () => {
-      const owners = process.listenerCount('SIGTERM')
-      await closeOnShutdown()
-      exitIfSoleShutdownOwner(owners)
+      await flushOnShutdown()
+      exitIfSoleShutdownOwner('SIGTERM')
     }
     Brainy.sigintListener = async () => {
-      const owners = process.listenerCount('SIGINT')
-      await closeOnShutdown()
-      exitIfSoleShutdownOwner(owners)
+      await flushOnShutdown()
+      exitIfSoleShutdownOwner('SIGINT')
     }
     Brainy.beforeExitListener = async () => {
       // Self-deregister FIRST: Node re-emits 'beforeExit' after every event-
@@ -2264,7 +2225,7 @@ export class Brainy<T = any> implements BrainyInterface<T> {
         process.off('beforeExit', Brainy.beforeExitListener)
         Brainy.beforeExitListener = undefined
       }
-      await closeOnShutdown()
+      await flushOnShutdown()
     }
     process.on('SIGTERM', Brainy.sigtermListener)
     process.on('SIGINT', Brainy.sigintListener)
@@ -2337,33 +2298,6 @@ export class Brainy<T = any> implements BrainyInterface<T> {
     return this.initialized
   }
 
-  /**
-   * @description Whether `close()` has BEGUN on this instance — in flight or
-   * already finished. The question a shutdown owner asks: this brain's
-   * teardown belongs to whoever started it, and a second party must not flush
-   * its components or release its writer lock underneath it.
-   *
-   * True from the synchronous moment `close()` is entered, so a listener that
-   * yields a tick and comes back reads the truth, not a stale "not yet".
-   * @returns `true` once a close has started.
-   */
-  get isClosing(): boolean {
-    return this._closeInFlight !== null
-  }
-
-  /**
-   * @description Whether `close()` has FINISHED tearing this instance down —
-   * durable steps attempted, writer lock released, instance terminal. A
-   * closed brain never re-initializes; every operation on it throws.
-   *
-   * True after a close that FAILED partway, too: such a brain still holds no
-   * writer lock and still serves nothing (see {@link close}).
-   * @returns `true` once the teardown has completed.
-   */
-  get isClosed(): boolean {
-    return this.closed
-  }
-
   /**
    * Promise that resolves when Brainy is fully initialized and ready to use
    *
@@ -3337,18 +3271,9 @@ export class Brainy<T = any> implements BrainyInterface<T> {
    * toward the next trigger. A failure is LOUD and leaves the writes counted
    * again — silence is not an option, and neither is a retry storm (the next
    * trigger re-attempts).
-   *
-   * COALESCING LIVES IN {@link flush}, NOT HERE. A kick that arrives while a
-   * flush is running used to return without doing anything — the writes it
-   * counted waited for some LATER trigger, and this method's guard also could
-   * not coalesce the flushes it does not start (the cross-process
-   * flush-request watcher and application `flush()` calls both go straight to
-   * `flush()`; two of those overlapping is exactly what production showed).
-   * The gate in `flush()` covers every caller: this kick now either runs the
-   * flush or joins the single queued follow-up, so the writes it counted are
-   * always someone's work, and there is still never a second concurrent run.
    */
   private kickBackgroundFlush(reason: 'threshold' | 'idle'): void {
+    if (this._persistBackgroundFlight) return
     const counted = this._persistDirtyWrites
     this._persistDirtyWrites = 0
     this._persistLastFlushAt = Date.now()
@@ -12978,58 +12903,7 @@ export class Brainy<T = any> implements BrainyInterface<T> {
    *   process.exit(0)
    * })
    */
-  flush(): Promise<void> {
-    // ---- THE SINGLE-FLIGHT GATE ----
-    // One flush body runs at a time, with at most ONE queued behind it. See
-    // `_flushInFlight` / `_flushFollowUp` for the measurement that required
-    // this. NOT `async`: the gate hands back the very promise the work is on,
-    // so joining callers share identity, not just an outcome. The gate is
-    // crossed BEFORE any await, so two callers in the same tick cannot both
-    // find the field empty.
-    if (this._flushInFlight) {
-      if (!this._flushFollowUp) {
-        // The running flush's failure is not this follow-up's failure: it is
-        // reported to ITS caller, and the queued work still gets its turn.
-        this._flushFollowUp = this._flushInFlight
-          .catch(() => {})
-          .then(() => {
-            this._flushFollowUp = null
-            return this.flush()
-          })
-      }
-      return this._flushFollowUp
-    }
-    const run = this._runFlush()
-    // `finally` and not `then`: a failed flush must still open the gate, or
-    // one rejection would wedge every later flush behind a promise nobody
-    // will ever settle.
-    const gated = run.finally(() => {
-      if (this._flushInFlight === gated) this._flushInFlight = null
-    })
-    this._flushInFlight = gated
-    return gated
-  }
-
-  /**
-   * @description The flush body — everything {@link flush} promises, run
-   * exactly once at a time by that method's single-flight gate. Private
-   * because non-overlap is part of the contract: there is no supported way to
-   * run two of these at once, and the counters here witness that.
-   * @returns Nothing.
-   */
-  private async _runFlush(): Promise<void> {
-    this._flushBodyRuns++
-    this._flushBodiesActive++
-    this._flushConcurrencyPeak = Math.max(this._flushConcurrencyPeak, this._flushBodiesActive)
-    try {
-      await this._flushSteps()
-    } finally {
-      this._flushBodiesActive--
-    }
-  }
-
-  /** @description The flush steps themselves. See {@link flush}. */
-  private async _flushSteps(): Promise<void> {
+  async flush(): Promise<void> {
     await this.ensureInitialized()
 
     // Read-only instances have no buffered writes to flush. close() may call
@@ -20276,42 +20150,11 @@ export class Brainy<T = any> implements BrainyInterface<T> {
    *
    * The original failure is never swallowed: it is narrated with what it costs
    * the next open, then rethrown to the caller.
-   *
-   * IDEMPOTENT AND RE-ENTRANT. The teardown below runs ONCE. Concurrent
-   * callers share the one in-flight promise and settle together; a caller
-   * arriving after it finished gets that same settled promise (close is
-   * terminal — there is nothing left to redo, and a failed close has already
-   * released the lock and set `closed`). This is what makes the shutdown
-   * ownership question answerable at all: whoever calls first owns the close,
-   * everyone else — including the engine's own signal handler — joins it or
-   * steps aside. See `_closeInFlight`.
    * @returns Nothing.
    * @throws The first failure from the durable close steps, after the
    *   terminal releases have run.
    */
-  close(): Promise<void> {
-    // NOT `async`: an async wrapper allocates a FRESH promise per call, so
-    // callers would hold different handles to the same work. Returning the
-    // stored promise itself makes "one close" observable identity, not just
-    // observable behaviour. The gate is crossed with NO await before it, so
-    // two callers in the same tick — and a signal handler resuming mid-close
-    // — always see the same answer; `isClosing` is true from this assignment
-    // onward. (`_closeOnce()` is async, so a failure is always a rejection,
-    // never a synchronous throw out of this method.)
-    if (this._closeInFlight) return this._closeInFlight
-    const run = this._closeOnce()
-    this._closeInFlight = run
-    return run
-  }
-
-  /**
-   * @description The close body — everything {@link close} promises, run
-   * exactly once by that method's gate.
-   * @returns Nothing.
-   * @throws The first failure from the durable close steps, after the
-   *   terminal releases have run.
-   */
-  private async _closeOnce(): Promise<void> {
+  async close(): Promise<void> {
     if (this._pendingEmbedIds.size === 0) await this.writeEmbedLowWater()
     let closeFailure: unknown = null
     try {
@@ -20400,19 +20243,6 @@ export class Brainy<T = any> implements BrainyInterface<T> {
     if (this._persistBackgroundFlight) {
       await this._persistBackgroundFlight.catch(() => {})
     }
-    // Drain the flush chain itself: the running flush AND the single follow-up
-    // queued behind it. The cadence's own handle above covers only the flushes
-    // the cadence started — a flush-request from another process, or an
-    // application's own flush() racing this close, is on the chain and nowhere
-    // else, and a flush landing mid-close writes behind the close's work.
-    // Bounded by construction: at most one follow-up exists, and awaiting it
-    // awaits its leader too, so the second pass is a no-op unless a writer
-    // raced this close.
-    for (let pass = 0; pass < 2; pass++) {
-      const chain = this._flushFollowUp ?? this._flushInFlight
-      if (!chain) break
-      await chain.catch(() => {})
-    }
 
     // Cancel any pending post-import background deduplication FIRST — it is a
     // writer (merge-deletes), and no delete pass may start mid- or post-close.

tests/integration/shutdown-single-owner.test.ts

@@ -1,405 +0,0 @@
-/**
- * @module tests/integration/shutdown-single-owner
- * @description ONE SHUTDOWN, ONE OWNER.
- *
- * MEASURED IN PRODUCTION. A host that owns its own shutdown — one SIGTERM
- * listener calling `close()` on every pooled store — ran head-on into the
- * engine's own signal handler, which iterated every live instance, flushed its
- * components in parallel, and released its writer lock in a `finally`. Two
- * teardowns of the same brain at the same moment. The log shape:
- *
- *   "Shutdown signal received - flushing pending data..."   (SIGTERM)
- *   ...148 seconds of silence...
- *   "Flushed successfully (1 instance)"
- *   ...the host's pool close of that same store returns 1s later
- *
- * 149s for the one store with engine work in flight, against 24s for its six
- * idle siblings. The same race in a local reproduction printed
- * `Failed to flush one Brainy instance on shutdown: Writer fence lost … the
- * lock file is gone` — the handler observing a lock the close it was racing
- * had already released.
- *
- * The contract pinned here:
- *   (a) A host owner and the engine's hooks both live: EXACTLY ONE close runs
- *       per brain, no fence is lost, both durability markers are written, the
- *       process exits 0, and the reopen adopts rather than folding.
- *   (b) No host owner: the engine's handler closes every instance by the same
- *       `close()` path — markers written, clean exit.
- *   (c) `close()` is idempotent and re-entrant: concurrent callers share ONE
- *       execution and all of them settle.
- *   (d) Flush is single-flight: N kicks during a running flush arm exactly one
- *       follow-up, and two flush bodies never overlap.
- */
-
-import { describe, it, expect, beforeEach, afterEach } from 'vitest'
-import { mkdtempSync, rmSync, existsSync, readFileSync, writeFileSync } from 'node:fs'
-import { spawn } from 'node:child_process'
-import { tmpdir } from 'node:os'
-import { join } from 'node:path'
-import { Brainy } from '../../src/brainy.js'
-import { NounType } from '../../src/types/graphTypes.js'
-
-const REPO_ROOT = process.cwd()
-const TSX = join(REPO_ROOT, 'node_modules', '.bin', 'tsx')
-const BRAINY_SRC = join(REPO_ROOT, 'src', 'brainy.ts')
-
-function makeTempDir(prefix: string): string {
-  return mkdtempSync(join(tmpdir(), prefix))
-}
-
-/** The writer lock's clean-close record — written by `releaseWriterLock()`. */
-const closeRecordPath = (dir: string) => join(dir, 'locks', '_writer.close')
-/**
- * The generation store's clean-shutdown marker — the adopt-vs-fold gate.
- * (`FileSystemStorage` gzips raw objects, so the file on disk carries `.gz`;
- * both spellings are accepted so the pin survives a compression change.)
- */
-const cleanShutdownWritten = (dir: string) =>
-  existsSync(join(dir, '_system', 'clean-shutdown.json.gz')) ||
-  existsSync(join(dir, '_system', 'clean-shutdown.json'))
-
-/**
- * Write a child script and start it under tsx, in its OWN process group so a
- * group-wide signal reaches the grandchild that actually holds the writer
- * lock. (A file, not `tsx -e`: the eval form compiles to CommonJS, which has
- * no top-level await.)
- */
-function startChild(scriptDir: string, body: string): ReturnType<typeof spawn> {
-  const scriptPath = join(scriptDir, 'child-process.mts')
-  writeFileSync(scriptPath, body)
-  return spawn(TSX, [scriptPath], {
-    cwd: REPO_ROOT,
-    stdio: ['ignore', 'pipe', 'pipe'],
-    detached: true
-  })
-}
-
-/** Start a child and resolve once it prints READY, collecting all its output. */
-function startAndAwaitReady(
-  scriptDir: string,
-  body: string
-): Promise<{ child: ReturnType<typeof spawn>; output: () => string }> {
-  const child = startChild(scriptDir, body)
-  let out = ''
-  child.stdout?.on('data', (d) => { out += String(d) })
-  child.stderr?.on('data', (d) => { out += String(d) })
-  return new Promise((resolvePromise, rejectPromise) => {
-    const timer = setTimeout(
-      () => rejectPromise(new Error(`child never became READY:\n${out}`)),
-      120_000
-    )
-    child.stdout?.on('data', () => {
-      if (out.includes('READY')) {
-        clearTimeout(timer)
-        resolvePromise({ child, output: () => out })
-      }
-    })
-    child.on('exit', (code) => {
-      clearTimeout(timer)
-      if (!out.includes('READY')) rejectPromise(new Error(`child exited ${code} before READY:\n${out}`))
-    })
-  })
-}
-
-/** Capture console.warn/error/log lines emitted while `fn` runs. */
-async function captureConsole<T>(fn: () => Promise<T>): Promise<{ result: T; lines: string[] }> {
-  const lines: string[] = []
-  const orig = { log: console.log, warn: console.warn, error: console.error }
-  const sink = (...args: unknown[]) => { lines.push(args.map((a) => String(a)).join(' ')) }
-  console.log = sink as typeof console.log
-  console.warn = sink as typeof console.warn
-  console.error = sink as typeof console.error
-  try {
-    return { result: await fn(), lines }
-  } finally {
-    console.log = orig.log
-    console.warn = orig.warn
-    console.error = orig.error
-  }
-}
-
-/**
- * Reopen a store and assert the open ADOPTED: no crash-recovery fold, no
- * stale-lock verdict. This is the whole point of a close having run exactly
- * once — a fold is measured in tens of seconds on a real store.
- */
-async function expectCleanReopen(dir: string): Promise<void> {
-  const { result, lines } = await captureConsole(async () => {
-    const next = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
-    await next.init()
-    return next
-  })
-  try {
-    expect(lines.filter((l) => /log-authority recovery|unclean shutdown detected/i.test(l))).toEqual([])
-    expect(lines.filter((l) => /Overwriting stale writer lock|appears dead/i.test(l))).toEqual([])
-  } finally {
-    await result.close()
-  }
-}
-
-/** The child's counts of closes entered and close bodies run, per brain. */
-function readResult(
-  resultPath: string,
-  out: string
-): { entries: Record<string, number>; bodies: Record<string, number>; releases: Record<string, number> } {
-  if (!existsSync(resultPath)) throw new Error(`child wrote no result file:\n${out}`)
-  return JSON.parse(readFileSync(resultPath, 'utf-8'))
-}
-
-/**
- * The child-side instrumentation, shared by (a) and (b): count how many times
- * `close()` is ENTERED per brain and how many times its body actually RUNS.
- * The counting wrapper is an OWN property, so it shadows the prototype for
- * every caller — including the engine's own signal handler, which calls
- * `instance.close()`.
- *
- * `report()` writes SYNCHRONOUSLY to a file: it runs on the way out of the
- * process (the engine's handler calls `process.exit(0)` when it is the sole
- * shutdown owner), and a `console.log` to a pipe is asynchronous and can be
- * dropped by that exit.
- */
-function childCounters(resultPath: string): string {
-  return `
-  const entries = {}
-  const bodies = {}
-  const releases = {}
-  function instrument(name, brain) {
-    entries[name] = 0
-    bodies[name] = 0
-    releases[name] = 0
-    const enter = brain.close.bind(brain)
-    brain.close = () => { entries[name]++; return enter() }
-    const durable = brain.closeDurableSteps.bind(brain)
-    brain.closeDurableSteps = () => { bodies[name]++; return durable() }
-    // The writer lock is the ownership witness: the old handler released it
-    // in its own finally, on top of the owner's close doing the same.
-    const storage = brain.storage
-    const release = storage.releaseWriterLock.bind(storage)
-    storage.releaseWriterLock = () => { releases[name]++; return release() }
-  }
-  const report = () => {
-    __writeFileSync(${JSON.stringify(resultPath)}, JSON.stringify({ entries, bodies, releases }))
-  }
-`
-}
-
-describe('shutdown has exactly one owner', () => {
-  let dirA: string
-  let dirB: string
-  let scriptDir: string
-  let resultPath: string
-
-  beforeEach(() => {
-    dirA = makeTempDir('brainy-shutdown-owner-a-')
-    dirB = makeTempDir('brainy-shutdown-owner-b-')
-    scriptDir = makeTempDir('brainy-shutdown-owner-script-')
-    resultPath = join(scriptDir, 'result.json')
-  })
-
-  afterEach(() => {
-    for (const d of [dirA, dirB, scriptDir]) {
-      try { rmSync(d, { recursive: true, force: true }) } catch { /* ignore */ }
-    }
-  })
-
-  it('(a) a host owner closes both brains and the engine handler steps aside', async () => {
-    const script = `
-      import { writeFileSync as __writeFileSync } from 'node:fs'
-      import { Brainy } from ${JSON.stringify(BRAINY_SRC)}
-      const a = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: ${JSON.stringify(dirA)} } })
-      const b = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: ${JSON.stringify(dirB)} } })
-      await a.init()
-      await b.init()
-      await a.add({ data: 'row in brain a', type: 'concept' })
-      await b.add({ data: 'row in brain b', type: 'concept' })
-      ${childCounters(resultPath)}
-      instrument('a', a)
-      instrument('b', b)
-      // THE HOST'S OWN SHUTDOWN OWNER, registered after the engine's hooks —
-      // the ordinary shape: the pool was built before the signal wiring.
-      process.on('SIGTERM', async () => {
-        await Promise.all([a.close(), b.close()])
-        // Stay alive a beat so the engine's deferred handler gets its turn and
-        // has to decide what to do about two already-closed brains.
-        await new Promise((r) => setTimeout(r, 1500))
-        report()
-        process.exit(0)
-      })
-      console.log('READY')
-      setInterval(() => {}, 1000)
-    `
-    const { child, output } = await startAndAwaitReady(scriptDir, script)
-
-    process.kill(-(child.pid as number), 'SIGTERM')
-    const code = await new Promise<number | null>((r) => child.on('exit', (c) => r(c)))
-    // The tsx wrapper's exit event and the grandchild that actually held the
-    // locks are asynchronous with each other — let its last writes land.
-    await new Promise<void>((r) => setTimeout(r, 750))
-    const out = output()
-
-    // The process shut down cleanly.
-    expect(code, `child output:\n${out}`).toBe(0)
-
-    // EXACTLY ONE close per brain — entered once, body run once. A second
-    // entry would mean the engine's handler closed a brain its owner was
-    // already closing; a second body would mean close() is not single-flight.
-    const { entries, bodies, releases } = readResult(resultPath, out)
-    expect(entries).toEqual({ a: 1, b: 1 })
-    expect(bodies).toEqual({ a: 1, b: 1 })
-    // ...and the writer lock was given up exactly once per brain. This is the
-    // assertion that fails on the old handler, which released the lock in its
-    // own `finally` on top of the owner's close doing the same — two owners.
-    expect(releases).toEqual({ a: 1, b: 1 })
-
-    // The engine's handler ran (it announced the signal) and stepped aside for
-    // both brains rather than touching them. setImmediate lands in the check
-    // phase of the same loop turn, so a close that has begun cannot have
-    // finished — it is still in flight when the handler looks.
-    expect(out).toContain('Shutdown signal received')
-    expect(out).toMatch(/2 Brainy instances are already closing/)
-
-    // Nothing was taken out from under the owner, and nothing failed.
-    expect(out).not.toMatch(/Writer fence lost/i)
-    expect(out).not.toMatch(/Failed to (flush|close) one Brainy instance/i)
-
-    // Both durability markers, both brains: the writer lock's clean-close
-    // record and the generation store's clean-shutdown marker.
-    for (const dir of [dirA, dirB]) {
-      expect(existsSync(closeRecordPath(dir)), `clean-close record missing in ${dir}`).toBe(true)
-      expect(cleanShutdownWritten(dir), `clean-shutdown marker missing in ${dir}`).toBe(true)
-    }
-
-    // And the next open adopts instead of folding.
-    await expectCleanReopen(dirA)
-    await expectCleanReopen(dirB)
-  }, 240_000)
-
-  it('(b) with no host owner the engine closes every instance the same way', async () => {
-    const script = `
-      import { writeFileSync as __writeFileSync } from 'node:fs'
-      import { Brainy } from ${JSON.stringify(BRAINY_SRC)}
-      const a = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: ${JSON.stringify(dirA)} } })
-      const b = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: ${JSON.stringify(dirB)} } })
-      await a.init()
-      await b.init()
-      await a.add({ data: 'row in brain a', type: 'concept' })
-      await b.add({ data: 'row in brain b', type: 'concept' })
-      ${childCounters(resultPath)}
-      instrument('a', a)
-      instrument('b', b)
-      process.on('exit', report)
-      console.log('READY')
-      setInterval(() => {}, 1000)
-    `
-    const { child, output } = await startAndAwaitReady(scriptDir, script)
-
-    process.kill(-(child.pid as number), 'SIGTERM')
-    const code = await new Promise<number | null>((r) => child.on('exit', (c) => r(c)))
-    // The tsx wrapper's exit event and the grandchild that actually held the
-    // locks are asynchronous with each other — let its last writes land.
-    await new Promise<void>((r) => setTimeout(r, 750))
-    const out = output()
-
-    expect(code, `child output:\n${out}`).toBe(0)
-
-    // The engine owned this shutdown: one close per brain, through close().
-    const { entries, bodies, releases } = readResult(resultPath, out)
-    expect(entries).toEqual({ a: 1, b: 1 })
-    expect(bodies).toEqual({ a: 1, b: 1 })
-    expect(releases).toEqual({ a: 1, b: 1 })
-    expect(out).toContain('Shutdown signal received')
-    expect(out).toMatch(/Flushed successfully \(2 instances\)/)
-    expect(out).not.toMatch(/Writer fence lost/i)
-    expect(out).not.toMatch(/Failed to (flush|close) one Brainy instance/i)
-
-    for (const dir of [dirA, dirB]) {
-      expect(existsSync(closeRecordPath(dir)), `clean-close record missing in ${dir}`).toBe(true)
-      expect(cleanShutdownWritten(dir), `clean-shutdown marker missing in ${dir}`).toBe(true)
-    }
-
-    await expectCleanReopen(dirA)
-    await expectCleanReopen(dirB)
-  }, 240_000)
-
-  it('(c) two concurrent close() callers share ONE execution, and both settle', async () => {
-    const brain = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dirA } })
-    await brain.init()
-    await brain.add({ data: 'one row', type: NounType.Concept })
-
-    const inner = brain as unknown as { closeDurableSteps: () => Promise<void> }
-    const durable = inner.closeDurableSteps.bind(inner)
-    let bodies = 0
-    inner.closeDurableSteps = () => { bodies++; return durable() }
-
-    expect(brain.isClosing).toBe(false)
-    expect(brain.isClosed).toBe(false)
-
-    const first = brain.close()
-    // The state is observable IMMEDIATELY — a signal handler that yields a
-    // tick and comes back must not read a stale "not yet".
-    expect(brain.isClosing).toBe(true)
-    const second = brain.close()
-    expect(first === second, 'concurrent callers must share the one promise').toBe(true)
-
-    await Promise.all([first, second])
-    expect(bodies).toBe(1)
-    expect(brain.isClosed).toBe(true)
-
-    // A caller arriving after the close finished gets the same settled answer,
-    // and nothing runs again.
-    await brain.close()
-    expect(bodies).toBe(1)
-
-    expect(existsSync(closeRecordPath(dirA))).toBe(true)
-    expect(cleanShutdownWritten(dirA)).toBe(true)
-  }, 120_000)
-
-  it('(d) N kicks during a running flush arm exactly one follow-up, never a second flush', async () => {
-    const brain = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dirA } })
-    await brain.init()
-
-    const inner = brain as unknown as {
-      _flushBodyRuns: number
-      _flushConcurrencyPeak: number
-      _flushInFlight: Promise<void> | null
-      _flushFollowUp: Promise<void> | null
-      _persistBackgroundFlight: Promise<void> | null
-      metadataIndex: { flush: () => Promise<void> }
-      kickBackgroundFlush: (reason: 'threshold' | 'idle') => void
-    }
-
-    // Widen the flush body's window so the kicks land INSIDE it — the
-    // production shape, where two flushes overlapped 3s apart.
-    const metaFlush = inner.metadataIndex.flush.bind(inner.metadataIndex)
-    inner.metadataIndex.flush = async () => {
-      await new Promise((r) => setTimeout(r, 400))
-      return metaFlush()
-    }
-
-    await brain.add({ data: 'a write to flush', type: NounType.Concept })
-    const runsBefore = inner._flushBodyRuns
-
-    const leader = brain.flush()
-    await new Promise((r) => setTimeout(r, 50)) // the leader is inside its body
-    expect(inner._flushInFlight, 'a flush is running').not.toBeNull()
-
-    // The cadence kicks — the door named in the defect — plus direct callers
-    // (an application flush, the cross-process flush-request watcher).
-    for (let i = 0; i < 5; i++) inner.kickBackgroundFlush('threshold')
-    const direct = [brain.flush(), brain.flush(), brain.flush()]
-
-    // EXACTLY ONE follow-up is armed, however many callers arrived.
-    expect(inner._flushFollowUp, 'the eight kicks armed one follow-up').not.toBeNull()
-
-    await Promise.all([leader, ...direct, inner._persistBackgroundFlight ?? Promise.resolve()])
-
-    // One leader + one follow-up. Not nine, and never two at once.
-    expect(inner._flushBodyRuns - runsBefore).toBe(2)
-    expect(inner._flushConcurrencyPeak).toBe(1)
-    expect(inner._flushInFlight).toBeNull()
-    expect(inner._flushFollowUp).toBeNull()
-
-    inner.metadataIndex.flush = metaFlush
-    await brain.close()
-  }, 120_000)
-})