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

tests/test_issue26_envfile.py

@@ -180,6 +180,47 @@ def test_a1_a_file_that_cannot_be_read_stops_both_loaders(tmp_path, kind):
         f.chmod(0o600)
 
 
+# Follow-up F2 (PR #43 claude S1): every main that loads the env file, with
+# arguments its parser accepts when it parses before loading.
+ENTRY_POINTS = {
+    "publish_event": ["--job", "abcd1234", "--event", "progress", "--registry-dir", "reg"],
+    "registry": [],
+    "job_subscriber": ["--job", "abcd1234", "--registry-dir", "reg"],
+    "cli": [],
+    "bench": [],
+    "heartbeat": ["--job", "abcd1234", "--interval", "30", "--registry-dir", "reg"],
+    "remote": ["run", "--session", "s", "--registry-dir", "reg"],
+}
+
+
+@pytest.mark.parametrize("kind", ["permission", "utf8"])
+@pytest.mark.parametrize("module", sorted(ENTRY_POINTS))
+def test_a1_python_entry_points_report_an_unreadable_file_in_one_line(tmp_path, module, kind):
+    """The wrapper's shape at every Python entry point: one `ERROR:` line
+    naming the path and the exception type, rc 1, no traceback, no value."""
+    f = tmp_path / "broken.env"
+    if kind == "permission":
+        if os.geteuid() == 0:
+            pytest.skip("root reads a 000 file")
+        f.write_text("PROBE_A=one\n")
+        f.chmod(0)
+        cause = "PermissionError"
+    else:
+        f.write_bytes(b"PROBE_A=one\nPROBE_B=\xff\xfe\n")
+        cause = "UnicodeDecodeError"
+    try:
+        # main() itself: `-m` adds runpy's warning (the package __init__ imports these modules)
+        code = f"import sys; from lib_py.delegation import {module} as m; sys.exit(m.main(sys.argv[1:]))"
+        res = subprocess.run([sys.executable, "-c", code, *ENTRY_POINTS[module]],
+                             capture_output=True, text=True, env=_env(tmp_path, f), cwd=str(tmp_path), timeout=60)
+    finally:
+        f.chmod(0o600)
+    assert res.returncode == 1, (res.returncode, res.stderr[-500:])
+    assert res.stderr.strip().splitlines() == [f"ERROR: {f}: cannot read ({cause})"], res.stderr[-500:]
+    assert "one" not in res.stdout + res.stderr
+    assert not (tmp_path / "reg").exists(), "nothing ran past the env file"
+
+
 def test_a1_a_nul_line_is_skipped_by_both_loaders(tmp_path):
     """Review R4: no environment can carry a NUL byte. Both loaders skip that
     line with a warning naming it (not its value) and keep the lines around it."""