fix(issue-12,8,7): keep broker password out of records, keep fresh install stamps, pack sibling workspaces

Issue #12 - MQTT_PASSWORD was copied into every job record, which any
sub-agent can read. BrokerConfig.to_registry_block no longer persists it;
broker_config_from_job layers the password back from the environment
(.mam.env) at connect time, so publish_event still connects from the record.
_atomic_write_record scrubs broker.password from any record it writes, and
`registry.py scrub-secrets [--dry-run]` migrates an existing registry.
auth_token/dispatch_token stay: the agent's own publish_event needs them.

Issue #8 - update.sh restored the pre-update asset_hashes.txt and version.txt
over the installer's fresh ones, so version.txt named the previous commit and
remove.sh backed up every pristine updated file as "locally modified". The
success path now keeps the installer's stamps and only merges install_state
keys the re-install did not write (gitignore_created); the failure path
still restores everything verbatim.

Issue #7 - the shim's new-session took the first same-cwd pane, always found
the full first workspace, judged it overflow and opened another workspace per
agent (4 + 1 + 1). It now walks every same-cwd workspace in pane order and
takes the first with an idle pane or room in its 2xK grid; a workspace is
created only when all are full (4 + 2).

Tests: test_issue7_workspace_packing.py (3; the mock herdr gains an opt-in
per-workspace 2x2 geometry), test_issue8_update_state.py (1, real
install+update cycle), test_issue12_registry_secrets.py (4); registry CLI
snapshot and help capture refreshed for the intentional scrub-secrets
subcommand; registry.md documents the broker block.

Refs #12 #8 #7

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

.agents/skills/lib_py/delegation/mqtt_common.py

@@ -227,13 +227,19 @@ class BrokerConfig:
         return asdict(self)
 
     def to_registry_block(self) -> Dict[str, Any]:
-        """The subset that gets persisted into a job record's broker block."""
+        """The subset that gets persisted into a job record's broker block.
+
+        Never the password (Issue #12): every sub-agent can read the job
+        record, so a broker secret written there ends up in agent transcripts.
+        ``broker_config_from_job`` layers the block over the environment, so
+        the password is taken from ``MQTT_PASSWORD`` (``.mam.env``) at connect
+        time instead.
+        """
         return {
             "host": self.host,
             "port": self.port,
             "tls": self.tls,
             "username": self.username,
-            "password": self.password,
         }
 
 
@@ -393,12 +399,23 @@ def load_job(job_id: str, registry_dir: str = DEFAULT_REGISTRY_DIR) -> Dict[str,
         return json.load(fh)
 
 
+def _scrub_record_secrets(record: Dict[str, Any]) -> None:
+    """Issue #12: a broker password never belongs in a job record (see
+    ``BrokerConfig.to_registry_block``). Records written before that rule are
+    cleaned the next time anything writes them; ``registry.py scrub-secrets``
+    does it for a whole registry at once."""
+    broker = record.get("broker")
+    if isinstance(broker, dict):
+        broker.pop("password", None)
+
+
 def _atomic_write_record(job_id: str, registry_dir: str, record: Dict[str, Any]) -> None:
     """Write a record atomically: temp file in the same dir + os.replace.
 
     The rename is atomic on POSIX, so readers never observe a half-written
     file. Callers MUST already hold ``registry_lock`` for read-modify-write
     correctness."""
+    _scrub_record_secrets(record)
     Path(registry_dir).mkdir(parents=True, exist_ok=True)
     path = _job_path(job_id, registry_dir)
     fd, tmp = tempfile.mkstemp(dir=str(path.parent), prefix=f".{job_id}.", suffix=".tmp")