fix(newos4): rollback keeps scaffolding, checkpoints cannot collide, tests gate the build

Review of the 08:30 implementer run (v4.6.102, checkpoint name fix). The shipped fix was
correct; these are the defects it introduced or left behind, each measured first.

- virtual-fs.js rollback(): the snapshot strips _snapshots/_sessions/.trash for bloat. Restoring
  it verbatim deleted every checkpoint, every agent session and the trash, made rollback
  irreversible and unrepeatable. Re-attach the live copies after the root swap.
- checkpoint(): names are millisecond-resolution, so tight calls overwrote each other
  (measured 6 calls -> 3 snapshots). Dedupe with a -N suffix, refuse names containing "/"
  (written but unlistable), and prune by snapshot createdAt instead of filename sort, which
  let a custom name ("aaa-oldest") evict newer auto-named checkpoints.
- module-predictor.js: legacy pre-v2 points have no `usable`, so a 0.079 s aborted run
  re-entered similarity as evidence and floored every prediction at 1 s. Backfill `usable`
  from the measurement on load, drop the ones it rejects, add a belt-and-braces guard in
  _findSimilar and count only usable points as actual executions.
- newos4-maintain.py: run every node-runnable modules/test/test-*.js on each maintenance pass.
  The v4.6.102 regression was written but no job ever executed it.
- newos4-steer.py: `done` now requires --commit <sha> that exists in the repo, and gains
  `reopen`. A written plan was being closed as done at 06:17 while the predictor fix shipped
  nowhere, so the implementer's pre-flight queue was empty.
- steering.json: predictor item reopened, checkpoint item stamped with f7249ff.
- maintenance board: MAINT-002/005/015 were fixed in v4.6.81-85 but still listed open/high;
  closed with their commit ids, and MAINT-010/016 annotated with the probes that keep them open.

Tests: test-vfs-checkpoint 23/23 (RED 14/9 before), test-predictor-accuracy 38/38
(T1-T3 RED on HEAD), maintain --fix all PASS, browser round-trip
"Checkpoint created: <name>" -> "Rolled back to checkpoint: <name>" on v4.6.103.

Also carries the already-deployed 2026-10-26 syntax-gate hunk in newos4-maintain.py (syntax_failures + gated rebuild) that had never been committed.

1 files changed, 33 insertions, 0 deletions

diff --git a/modules/test/test-predictor-accuracy.js b/modules/test/test-predictor-accuracy.js
index 3688b03..74f0fcc 100644
--- a/modules/test/test-predictor-accuracy.js
+++ b/modules/test/test-predictor-accuracy.js
@@ -247,5 +247,38 @@ function ok(name, cond, detail) {
     ok('S3 pending consumed', p._pending.length === 0);
 }
 
+// T. v1 payload carrying an aborted garbage point must not train similarity (2026-10-27)
+{
+    const { p, term, out } = mk();
+    const feats = p._extractFeatures('read the logs');
+    term.fs.fsWriteJSON('/system/metrics/predictor.json', {
+        dataPoints: [{ features: feats, observedDuration: 0.079, observedTurns: 1 },
+                     { features: feats, observedDuration: 30, observedTurns: 3 }],
+        predictions: 2
+    });
+    p._loadFromVFS();
+    ok('T1 legacy aborted point dropped on load', p._dataPoints.length === 1, 'n=' + p._dataPoints.length);
+    const similar = p._findSimilar(p._extractFeatures('read the logs'));
+    ok('T2 similarity ignores the aborted point',
+        similar.length === 1 && similar[0].observedDuration === 30,
+        JSON.stringify(similar.map(s => s.observedDuration)));
+    out.length = 0; p.showStatus();
+    const line = out.find(l => l.includes('Actual executions')) || '';
+    ok('T3 status counts only usable executions', /Actual executions:\s*1\s*$/.test(line.trim()), line.trim());
+}
+
+// U. a lone aborted point cannot floor the next prediction
+{
+    const { p, term } = mk();
+    term.fs.fsWriteJSON('/system/metrics/predictor.json', {
+        dataPoints: [{ features: { hasRead: true }, observedDuration: 0.079, observedTurns: 1 }],
+        predictions: 1
+    });
+    p._loadFromVFS();
+    const pred = p.notePrediction('read the logs', 'test');
+    ok('U1 prediction is not floored by a lone aborted point', pred && pred.floored === false,
+        JSON.stringify(pred && { duration: pred.duration, floored: pred.floored }));
+}
+
 console.log(passes + '/' + (passes + fails) + ' PASS');
 process.exit(fails ? 1 : 0);