fix: pre-landing review round — 8 auto-fixes + 8 accepted findings hardened

The ship review army (4 specialists + red-team + checklist, 29 findings)
produced 8 mechanical auto-fixes and 11 decisions; the accepted set:

- win32 slug parity completed: lib/bin-context.ts gains the remote-first
  outermost walk + degraded-cache self-heal the bash side got this wave —
  the two implementations now agree on the stray-marker live-bug shape,
  pinned by shared fixtures (multi-specialist 9/10 finding).
- probe honors the plan's bounded-read decision: 256KB prefix, extraction
  semantics mirrored from parseTranscriptJsonl so probe/prepare can never
  diverge on the same file (>1MB transcript test).
- policy normalize parity: bash normalize() now matches canonicalizeRemote
  on .git/-trailing and uppercase-.GIT shapes (7-shape corpus pinned two
  ways) — a deny for those shapes could previously slip the transcript gate.
- session-update reclaim is TOCTOU-safe (atomic mv-aside on both branches).
- settings-hook: unparseable settings.json errors instead of being replaced
  with {}; ensure-event keys on (event, source) so matcher changes update
  in place — never zero or two registrations.
- dot-only slug guard at both parse sites (hostile 'url = ..' can't escape
  projects/); enqueue tmp-file janitor (1h TTL, inside the drain lock);
  brain-sync .migrating never clobbered; drop-queue/status count .migrating;
  snapshot -o warning correct + surfaced in diff mode; version-bump test
  order-dependence removed; uninstall clears the advance stamp.

Deferred with record: slug heal-probe cost sentinel (P3 TODO), FF_OK
conflation (noted, misdiagnosis-only).

270 pass / 0 fail across the 10 touched suites.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bin/gstack-settings-hook

@@ -83,7 +83,17 @@ case "$ACTION" in
       const settingsPath = process.env.GSTACK_SETTINGS_PATH;
       const hookCmd = process.env.GSTACK_HOOK_CMD;
       let settings = {};
-      try { settings = JSON.parse(fs.readFileSync(settingsPath, "utf8")); } catch {}
+      // An EXISTING file that does not parse must never be rewritten: the
+      // old catch{} folded it to {} and the atomic write below replaced the
+      // user permissions/env/other hooks with just ours. Refuse loudly.
+      if (fs.existsSync(settingsPath)) {
+        try { settings = JSON.parse(fs.readFileSync(settingsPath, "utf8")); }
+        catch (e) {
+          console.error("error: " + settingsPath + " exists but is not valid JSON (" +
+            (e && e.message ? e.message : e) + "); refusing to rewrite it. Fix or move the file, then re-run.");
+          process.exit(1);
+        }
+      }
       if (!settings.hooks) settings.hooks = {};
       if (!settings.hooks.SessionStart) settings.hooks.SessionStart = [];
       const exists = settings.hooks.SessionStart.some(entry =>
@@ -97,7 +107,7 @@ case "$ACTION" in
       const tmp = settingsPath + ".tmp";
       fs.writeFileSync(tmp, JSON.stringify(settings, null, 2) + "\n");
       fs.renameSync(tmp, settingsPath);
-    ' 2>/dev/null
+    '
     ;;
 
   remove)
@@ -178,18 +188,34 @@ case "$ACTION" in
       const ensure = process.env.GSTACK_ENSURE === "1";
 
       let settings = {};
-      try { settings = JSON.parse(fs.readFileSync(settingsPath, "utf8")); } catch {}
+      // An EXISTING file that does not parse must never be rewritten: the
+      // old catch{} folded it to {} and the atomic write below replaced the
+      // user permissions/env/other hooks with just ours. Refuse loudly.
+      if (fs.existsSync(settingsPath)) {
+        try { settings = JSON.parse(fs.readFileSync(settingsPath, "utf8")); }
+        catch (e) {
+          console.error("error: " + settingsPath + " exists but is not valid JSON (" +
+            (e && e.message ? e.message : e) + "); refusing to rewrite it. Fix or move the file, then re-run.");
+          process.exit(1);
+        }
+      }
 
       const before = JSON.stringify(settings, null, 2);
 
       if (!settings.hooks) settings.hooks = {};
       if (!settings.hooks[event]) settings.hooks[event] = [];
 
+      // Identity key is (event, source): any existing entry carrying OUR
+      // source tag for this event IS the entry to compare/update — a matcher
+      // change must update it in place, never push a SECOND gstack entry
+      // (the old key included the matcher, so a future matcher change would
+      // have duplicated the registration). Untagged legacy entries are still
+      // adopted when both matcher and command line up.
       const matchesEntry = (entry) => {
+        if (entry._gstack_source === source) return true;
         const sameMatcher = (entry.matcher || "") === matcher;
         const sameCommand = entry.hooks && entry.hooks[0] && entry.hooks[0].command === cmd;
-        const sameSource = entry._gstack_source === source;
-        return sameMatcher && (sameSource || sameCommand);
+        return sameMatcher && sameCommand;
       };
 
       let existing = settings.hooks[event].find(matchesEntry);
@@ -202,6 +228,10 @@ case "$ACTION" in
       if (existing) {
         existing.hooks = [hookEntry];
         existing._gstack_source = source;
+        // Keep the matcher current too — under the (event, source) key the
+        // matched entry may carry a stale matcher.
+        if (matcher) existing.matcher = matcher;
+        else delete existing.matcher;
       } else {
         const newEntry = { _gstack_source: source, hooks: [hookEntry] };
         if (matcher) newEntry.matcher = matcher;