fix(followups): F2 review R1 - a failed env load is not cached as loaded

ensure_env_loaded() set _env_loaded before _load_dotenv() ran. With F2,
load_env_or_report() turns the EnvFileError into a return value, so a second
main() in the same process skipped the unreadable file and ran unconfigured
(codex R1: registry.main twice -> rc 1 then rc 0 with a job registered; a
repaired file was never read). The flag is now set only after a successful
load: a failure is retried on the next call, a success still loads once.
envfile parses the whole file before applying, so a failed load sets nothing.

MESSAGING.md: the one-line ERROR is the Python entry points'; the wrapper
adds its own "ERROR: cannot load <path>" line (codex, minor).

Test: in one process, registry.main twice on an undecodable file is rc 1
both times, prints the ERROR line twice and registers nothing; the repaired
file is applied on the next call; a later change is not re-read. At 95eabc6
it fails with rc [1, 0], one job registered and the value unset.

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

@@ -122,8 +122,10 @@ def ensure_env_loaded(workspace_dir: Optional[str] = None) -> None:
     global _env_loaded
     if _env_loaded:
         return
-    _env_loaded = True
     _load_dotenv(workspace_dir)
+    # Only a load that succeeded is cached: after an EnvFileError the next
+    # call reads the file again (load_env_or_report returns, it does not exit).
+    _env_loaded = True
 
 
 def load_env_or_report() -> bool:

MESSAGING.md

@@ -366,7 +366,7 @@ The subscriber acts as the central execution watchdog:
 * **`.mam.env` Resolution Hierarchy (`_load_dotenv`)**:
   Configuration files are resolved with strict precedence rules:
   1. **OS Environment Precedence**: Any variable already defined in `os.environ` is preserved and never overwritten by file-based configs.
-  2. **Explicit Override (`MAM_ENV_FILE`)**: If `MAM_ENV_FILE` is set, only that specific file is parsed. If the specified file does not exist, it is skipped silently and ambient search is refused (no fallback to unintended parent configs): the process runs on its environment and the defaults. If it exists but cannot be read or decoded, that is an error (`EnvFileError`): the wrapper and the Python entry points print one `ERROR: <path>: cannot read (<exception type>)` line and exit 1.
+  2. **Explicit Override (`MAM_ENV_FILE`)**: If `MAM_ENV_FILE` is set, only that specific file is parsed. If the specified file does not exist, it is skipped silently and ambient search is refused (no fallback to unintended parent configs): the process runs on its environment and the defaults. If it exists but cannot be read or decoded, that is an error (`EnvFileError`): the Python entry points print one `ERROR: <path>: cannot read (<exception type>)` line and exit 1; the wrapper prints that line followed by `ERROR: cannot load <path> (see the line above)` and exits 1.
   3. **Workspace Root Auto-Discovery**: If `MAM_ENV_FILE` is not set, the resolver searches candidate paths in order: `MAM_REAL_ROOT`, `WORKSPACE_ROOT`, upward directory walk searching for `.agents` or `.git` boundary markers, and `os.getcwd()`.
   4. **Public Broker Security Alert (B-17)**: If the final resolved host falls back to the public sandbox `broker.hivemq.com`, a prominent security warning is emitted.
 * **Broker Config Resolution (`broker_config_from_job`)**:

tests/test_issue26_envfile.py

@@ -449,3 +449,40 @@ def test_a7_a_missing_explicit_file_loads_nothing_and_says_nothing(tmp_path):
     assert _python_values(env, ["PROBE_AMBIENT"]) == {"PROBE_AMBIENT": "<unset>"}
     doc = next(l for l in (REPO_ROOT / "MESSAGING.md").read_text().splitlines() if "Explicit Override (`MAM_ENV_FILE`)" in l)
     assert "does not exist, it is skipped silently" in doc and "an error is logged" not in doc, doc
+
+
+_RETRY_PROBE = r"""
+import json, os, sys
+from pathlib import Path
+from lib_py.delegation import mqtt_common, registry
+env_file, jobs = Path(sys.argv[1]), sys.argv[2]
+argv = ["--registry-dir", jobs, "register", "--prompt", "retry probe"]
+out = {"rc": [registry.main(argv), registry.main(argv)]}
+out["registered"] = sorted(p.name for p in Path(jobs).glob("*.json")) if Path(jobs).exists() else []
+env_file.write_text("PROBE_CONFIG=from-file\n")
+out["recovered"] = [mqtt_common.load_env_or_report(), os.environ.get("PROBE_CONFIG")]
+env_file.write_text("PROBE_CONFIG=changed\n")
+out["cached"] = [mqtt_common.load_env_or_report(), os.environ.get("PROBE_CONFIG")]
+print(json.dumps(out))
+"""
+
+
+def test_a1_a_failed_load_is_not_cached_as_loaded(tmp_path):
+    """Review R1 (codex): load_env_or_report returns instead of exiting, so the
+    failure must not mark the env as loaded - in one process, a second main()
+    on the same unreadable file is rc 1 again and registers nothing, a repaired
+    file is read on the next call, and only a success is loaded once."""
+    f = tmp_path / "broken.env"
+    f.write_bytes(b"PROBE_CONFIG=from-file\nBAD=\xff\n")
+    jobs = tmp_path / "jobs"
+    env = _env(tmp_path, f)
+    env.pop("PROBE_CONFIG", None)
+    res = subprocess.run([sys.executable, "-c", _RETRY_PROBE, str(f), str(jobs)], capture_output=True, text=True,
+                         env=env, cwd=str(tmp_path), timeout=60)
+    assert res.returncode == 0, res.stderr[-800:]
+    got = json.loads(res.stdout.strip().splitlines()[-1])
+    assert got["rc"] == [1, 1], (got, res.stderr[-800:])
+    assert got["registered"] == [], got
+    assert res.stderr.count(f"ERROR: {f}: cannot read (UnicodeDecodeError)") == 2, res.stderr[-800:]
+    assert got["recovered"] == [True, "from-file"], got
+    assert got["cached"] == [True, "from-file"], "a successful load stays once per process"