fix(followups): F2 - Python entry points report an unreadable env file in one line

A .mam.env that exists but cannot be read or decoded stopped the Python
entry points with an EnvFileError traceback, while the wrapper printed one
`ERROR:` line and exited 1 (PR #43 review claude S1). The mains that load the
env file - publish_event, registry, job_subscriber, cli, bench, heartbeat and
remote - now call mqtt_common.load_env_or_report(), which prints
`ERROR: <path>: cannot read (<exception type>)` and lets the main return 1.
No value or file content is printed. ensure_env_loaded() still raises: no
library function exits the process.

Test: every entry point, for a 000 file and an undecodable one, ends with
exactly that line and rc 1 and creates nothing (14 cases; all 14 fail at
0051fd6 with a traceback).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HCGpJXhSZasJLU38ksDghe

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

@@ -21,6 +21,7 @@ import hmac
 import json
 import logging
 import os
+import sys
 import tempfile
 import time
 import uuid
@@ -110,9 +111,10 @@ def ensure_env_loaded(workspace_dir: Optional[str] = None) -> None:
     """Load the workspace env file exactly once per process (D6, issue #5 phase 1).
 
     This used to run at import time. Importing a library must not mutate
-    ``os.environ``, so every *process entry point* calls this instead:
+    ``os.environ``, so every *process entry point* calls this instead -
     ``publish_event.main``, ``registry.main``, ``job_subscriber.main``,
-    ``cli.main``, ``bench.main``, and reconcile.sh's embedded subscriber.
+    ``cli.main``, ``bench.main``, ``heartbeat.main`` and ``remote.main``
+    through :func:`load_env_or_report`, and reconcile.sh's embedded subscriber.
     Production semantics are unchanged because every production path passes
     through one of those, and OS env still wins over the file
     (see :func:`_parse_env_file`).
@@ -123,6 +125,20 @@ def ensure_env_loaded(workspace_dir: Optional[str] = None) -> None:
     _env_loaded = True
     _load_dotenv(workspace_dir)
 
+
+def load_env_or_report() -> bool:
+    """ensure_env_loaded() for a process entry point: an env file that exists
+    but cannot be read ends the process the way the wrapper does - one
+    `ERROR: <path>: cannot read (<exception type>)` line, no traceback, no
+    value - and the caller returns 1. False after printing; library code keeps
+    calling ensure_env_loaded() and never exits."""
+    try:
+        ensure_env_loaded()
+    except envfile.EnvFileError as e:
+        print(f"ERROR: {e}", file=sys.stderr)
+        return False
+    return True
+
 # --------------------------------------------------------------------------
 # Constants
 # --------------------------------------------------------------------------