fix(miner): compare-and-set the orphan reclaim so a stale probe cannot free a live re-acquired slot

packages/loopover-miner/lib/worktree-allocator.ts

@@ -239,17 +239,26 @@ function isSlotOrphaned(row: OrphanProbeRow, nowMs: number, maxLeaseMs: number,
   return false;
 }
 
-function reclaimOrphanedAllocations(db: DatabaseSync, nowMs: number, maxLeaseMs: number, hostId: string): void {
-  const orphans = db
-    .prepare("SELECT slot_index, owner_pid, owner_host, allocated_at FROM worktree_slots WHERE status = 'active'")
-    .all() as OrphanProbeRow[];
+/** Exported for the CAS regression test only — production callers go through the allocator handle. */
+export function reclaimOrphanedAllocations(db: DatabaseSync, nowMs: number, maxLeaseMs: number, hostId: string, probedRows?: OrphanProbeRow[]): void {
+  const orphans =
+    probedRows ??
+    (db
+      .prepare("SELECT slot_index, owner_pid, owner_host, allocated_at FROM worktree_slots WHERE status = 'active'")
+      .all() as OrphanProbeRow[]);
+  // COMPARE-AND-SET on the exact lease evidence the probe saw: between the SELECT above and this UPDATE, a
+  // peer process can legitimately free-and-re-acquire the same slot (the sweep runs on EVERY acquire since
+  // #8859, so the window is hit under real concurrency — CI reproduced duplicate paths). A re-acquired slot
+  // carries a fresh allocated_at (and usually a new owner), so guarding on the probed values makes a stale
+  // reclaim a no-op instead of force-freeing a live peer's allocation and double-booking the worktree.
   const reclaim = db.prepare(`
     UPDATE worktree_slots
     SET status = 'free', attempt_id = NULL, repo_full_name = NULL, owner_pid = NULL, owner_host = NULL, allocated_at = NULL
-    WHERE slot_index = ?
+    WHERE slot_index = ? AND status = 'active'
+      AND allocated_at IS ? AND owner_pid IS ? AND owner_host IS ?
   `);
   for (const row of orphans) {
-    if (isSlotOrphaned(row, nowMs, maxLeaseMs, hostId)) reclaim.run(row.slot_index);
+    if (isSlotOrphaned(row, nowMs, maxLeaseMs, hostId)) reclaim.run(row.slot_index, row.allocated_at, row.owner_pid, row.owner_host);
   }
 }
 

test/fixtures/miner-worktree-allocator/acquire-child.mjs

@@ -2,6 +2,13 @@
 // Cross-process helper for worktree-allocator collision tests (#4298).
 // Opens the shared store, waits for a stdin "go" signal, then calls acquire() so
 // multiple Node processes contend on BEGIN IMMEDIATE against the same dbPath.
+//
+// LEASE LIFECYCLE (#8992): a child that acquires successfully HOLDS its lease (process alive, allocator
+// open) until the test sends "done". Exiting right after acquire — the previous behavior — violated the
+// lease contract the allocator is built around: the same-host dead-pid fast path in every LATER child's
+// on-acquire sweep (#8859) then correctly reclaimed the dead child's slot and re-issued the same path,
+// which is exactly what the distinct-paths and capacity tests flaked on under CI load (4-of-5, then
+// 2-of-5 distinct). Production owners stay alive for the whole worktree lifetime; the fixture now does too.
 import { openWorktreeAllocator } from "../../../packages/loopover-miner/dist/lib/worktree-allocator.js";
 
 const [dbPath, worktreeBaseDir, maxConcurrencyStr, attemptId, repoFullName] = process.argv.slice(2);
@@ -17,23 +24,36 @@ const allocator = openWorktreeAllocator({
 });
 
 let started = false;
+let holdingLease = false;
 
 function runAcquire() {
   if (started) return;
   started = true;
   try {
     const allocation = allocator.acquire(attemptId, repoFullName);
+    holdingLease = true;
     process.stdout.write(`${JSON.stringify({ ok: true, allocation })}\n`);
-    process.exit(0);
+    // Stay alive: the lease is held until the test says "done".
   } catch (error) {
     const message = error instanceof Error ? error.message : String(error);
     process.stdout.write(`${JSON.stringify({ ok: false, message })}\n`);
-    process.exit(1);
-  } finally {
     allocator.close();
+    process.exit(1);
   }
 }
 
+function finish() {
+  if (!holdingLease) return;
+  holdingLease = false;
+  allocator.close();
+  process.exit(0);
+}
+
 process.stdin.setEncoding("utf8");
-process.stdin.on("data", () => runAcquire());
+let stdinBuffer = "";
+process.stdin.on("data", (chunk) => {
+  stdinBuffer += chunk;
+  if (stdinBuffer.includes("go\n")) runAcquire();
+  if (stdinBuffer.includes("done\n")) finish();
+});
 process.stdout.write("READY\n");

test/unit/miner-worktree-allocator-collisions.test.ts

@@ -62,7 +62,7 @@ function spawnAcquireChild(
   attemptId: string,
   maxConcurrency: number,
 ): ChildProcessWithoutNullStreams {
-  return spawn(
+  const child = spawn(
     process.execPath,
     [
       acquireChildScript,
@@ -74,6 +74,10 @@ function spawnAcquireChild(
     ],
     { stdio: ["pipe", "pipe", "pipe"] },
   );
+  // The done-broadcast can race a child that already exited (a rejected acquire exits immediately) — an
+  // unhandled EPIPE on its stdin must not crash the test run.
+  child.stdin.on("error", () => {});
+  return child;
 }
 
 async function waitForReady(child: ChildProcessWithoutNullStreams): Promise<void> {
@@ -102,29 +106,49 @@ async function runBarrieredAcquires(
   const children = attemptIds.map((attemptId) => spawnAcquireChild(paths, attemptId, maxConcurrency));
   await Promise.all(children.map((child) => waitForReady(child)));
   for (const child of children) child.stdin.write("go\n");
-  return Promise.all(
+  // #8992: results resolve from STDOUT, not exit — a successful child HOLDS its lease (process alive) until
+  // every result is observed. The previous exit-after-acquire lifecycle let later children's on-acquire
+  // sweeps legitimately reclaim the dead winners' slots and re-issue the same paths (the CI 4-of-5 /
+  // 2-of-5-distinct flake), and could hand the capacity test a third success at a 2-slot cap.
+  const results = await Promise.all(
     children.map(
       (child) =>
         new Promise<AcquireChildResult>((resolve, reject) => {
           let stdout = "";
-          child.stdout.on("data", (chunk) => {
+          const onData = (chunk: Buffer | string) => {
             stdout += chunk.toString();
-          });
-          child.once("error", reject);
-          child.once("exit", () => {
             const line = stdout
               .split("\n")
               .map((entry) => entry.trim())
               .find((entry) => entry.startsWith("{"));
-            if (!line) {
-              reject(new Error(`child produced no JSON result: ${stdout}`));
-              return;
+            if (line) {
+              child.stdout.off("data", onData);
+              resolve(JSON.parse(line) as AcquireChildResult);
             }
-            resolve(JSON.parse(line) as AcquireChildResult);
+          };
+          child.stdout.on("data", onData);
+          child.once("error", reject);
+          child.once("exit", () => {
+            if (!stdout.includes("{")) reject(new Error(`child exited with no JSON result: ${stdout}`));
           });
         }),
     ),
   );
+  // Every lease observed — release the survivors and wait for them to exit cleanly.
+  await Promise.all(
+    children.map(
+      (child) =>
+        new Promise<void>((resolve) => {
+          if (child.exitCode !== null) {
+            resolve();
+            return;
+          }
+          child.once("exit", () => resolve());
+          child.stdin.write("done\n");
+        }),
+    ),
+  );
+  return results;
 }
 
 afterEach(() => {

test/unit/miner-worktree-allocator.test.ts

@@ -5,6 +5,7 @@ import { afterEach, describe, expect, it, vi } from "vitest";
 import { DatabaseSync } from "node:sqlite";
 import {
   acquireWorktree,
+  reclaimOrphanedAllocations,
   closeDefaultWorktreeAllocator,
   isProcessAlive,
   openWorktreeAllocator,
@@ -231,3 +232,31 @@ describe("loopover-miner worktree allocator scaffolding (#4298)", () => {
     });
   });
 });
+
+describe("reclaim compare-and-set (#8918 follow-up: the duplicate-path race)", () => {
+  it("a stale probe snapshot must NOT free a slot a peer re-acquired between probe and apply", () => {
+    const dir = mkdtempSync(join(tmpdir(), "worktree-cas-"));
+    const dbPath = join(dir, "worktree-allocator.sqlite3");
+    const nowMs = Date.parse("2026-01-02T00:00:00.000Z");
+    const allocator = openWorktreeAllocator({ dbPath, worktreeBaseDir: join(dir, "wt"), maxConcurrency: 2, maxLeaseMs: 100, nowMs });
+    // An ancient lease: genuinely orphaned (a day past a 100ms lease) at probe time.
+    const db = new DatabaseSync(dbPath);
+    db.prepare("UPDATE worktree_slots SET status='active', attempt_id='ghost', owner_pid=999999, owner_host='other-host', allocated_at='2026-01-01T00:00:00.000Z' WHERE slot_index = 0").run();
+    const staleProbe = db.prepare("SELECT slot_index, owner_pid, owner_host, allocated_at FROM worktree_slots WHERE status = 'active'").all() as never;
+    // Between the probe and the apply, a PEER frees and re-acquires slot 0 — a fresh, live lease.
+    db.prepare("UPDATE worktree_slots SET attempt_id='live-peer', owner_pid=4242, owner_host='peer-host', allocated_at='2026-01-01T23:59:59.999Z' WHERE slot_index = 0").run();
+    // Applying the STALE snapshot must be a no-op: the lease evidence no longer matches.
+    reclaimOrphanedAllocations(db, nowMs, 100, "this-host", staleProbe);
+    const row = db.prepare("SELECT status, attempt_id FROM worktree_slots WHERE slot_index = 0").get() as { status: string; attempt_id: string };
+    expect(row.status).toBe("active");
+    expect(row.attempt_id).toBe("live-peer");
+    // And when the CURRENT row really is the aged-out lease (probe evidence matches), it frees.
+    db.prepare("UPDATE worktree_slots SET allocated_at='2026-01-01T00:00:00.000Z' WHERE slot_index = 0").run();
+    reclaimOrphanedAllocations(db, nowMs, 100, "this-host");
+    const freed = db.prepare("SELECT status FROM worktree_slots WHERE slot_index = 0").get() as { status: string };
+    expect(freed.status).toBe("free");
+    db.close();
+    allocator.close();
+    rmSync(dir, { recursive: true, force: true });
+  });
+});