fix(locks): the fence keys ownership on pid+hostname — a same-process re-open never fences its predecessor

The plant's integration lane caught it twice: the fence's startedAt-strict
comparison turned the documented same-process warn-and-take-over path (two
instances in one Node process — the server-restart test pattern, and the
shared-default-store pattern across test files) into a flush-killer: the
first instance's background flushes latched dead while its own process held
the lock ('PID N no longer holds the lock — it is now held by PID N').

Ownership is per-process: pid + hostname. startedAt stays in the lock for
observability but not in the fence — it protects nothing (a pid-recycled
successor's victim is a dead process that runs no fence checks) and it
convicted the innocent. Pinned: a same-process re-open leaves both
instances' flushes working; the cross-process eviction pins unchanged.

Verified under the lane's exact command: 102/102 files, 850 passed, exit 0.

tests/integration/writer-lock-fencing.test.ts

@@ -89,6 +89,23 @@ describe('writer-lock fencing', () => {
     expect(await brain.get(id)).not.toBeNull()
   }, 120000)
 
+  it('the fence does NOT fire on a same-process re-open — the documented warn-and-take-over contract stays benign', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-fence-samepid-'))
+    dirs.push(dir)
+    const first = await fsBrain(dir)
+    await first.add({ data: 'first instance write', type: NounType.Document, metadata: { n: 1 } })
+
+    // A second instance in the SAME process takes the lock over (fresh
+    // startedAt) — the pattern server-restart tests use. The first
+    // instance's background flushes must keep working: same pid + same
+    // hostname IS ownership. (The plant's integration lane caught the
+    // startedAt-strict fence latching exactly this shape dead.)
+    const second = await fsBrain(dir)
+    await second.add({ data: 'second instance write', type: NounType.Document, metadata: { n: 2 } })
+    await expect(first.flush()).resolves.toBeUndefined()
+    await expect(second.flush()).resolves.toBeUndefined()
+  }, 120000)
+
   it('THE FENCE: a forced-out writer fails its next flush typed and advances nothing', async () => {
     const dir = mkdtempSync(join(tmpdir(), 'brainy-fence-evict-'))
     dirs.push(dir)