diff --git a/.agents/skills/lib_py/loop/runner.py b/.agents/skills/lib_py/loop/runner.py
index cf9502a..2300e5d 100644
--- a/.agents/skills/lib_py/loop/runner.py
+++ b/.agents/skills/lib_py/loop/runner.py
@@ -469,12 +469,26 @@ class LoopRunner:
             # MAX_ARG_STRLEN (131,072 bytes on Linux), and a review prompt
             # carries the whole diff. The wrapper blocks until the job ends,
             # so nothing reads the file after it returns.
-            self.mam_dir.mkdir(parents=True, exist_ok=True)
-            with tempfile.NamedTemporaryFile("w", encoding="utf-8", dir=self.mam_dir,
-                                             prefix=f"prompt-{self.loop_id}-", suffix=".md",
-                                             delete=False) as fh:
-                fh.write(p_text)
-                prompt_file = fh.name
+            prompt_file = ""
+            try:
+                self.mam_dir.mkdir(parents=True, exist_ok=True)
+                with tempfile.NamedTemporaryFile("w", encoding="utf-8", dir=self.mam_dir,
+                                                 prefix=f"prompt-{self.loop_id}-", suffix=".md",
+                                                 delete=False) as fh:
+                    prompt_file = fh.name
+                    fh.write(p_text)
+            except OSError as e:
+                # The same class the shell paths handle (merge review H1): a
+                # partial file is removed and the submit fails like an exec
+                # error would, instead of the exception reaching the loop.
+                if prompt_file:
+                    try:
+                        os.unlink(prompt_file)
+                    except OSError:
+                        pass
+                msg = (f"cannot write the prompt file under {self.mam_dir}: {e} "
+                       f"(prompt {len(p_text.encode('utf-8'))} bytes)")
+                return subprocess.CompletedProcess(["bash", str(wrapper_script), "submit"], 126, "", msg)
             cmd = [
                 "bash", str(wrapper_script), "submit",
                 "--agent-session", self.session_label(agent_session),
diff --git a/.agents/skills/multi-agent-mux-delegate-job/multi-agent-mux-delegate-job b/.agents/skills/multi-agent-mux-delegate-job/multi-agent-mux-delegate-job
index 0791baf..d67ffc3 100755
--- a/.agents/skills/multi-agent-mux-delegate-job/multi-agent-mux-delegate-job
+++ b/.agents/skills/multi-agent-mux-delegate-job/multi-agent-mux-delegate-job
@@ -190,6 +190,7 @@ cmd_submit() {
     [[ -z "$PROMPT" ]] || { echo "submit takes --prompt or --prompt-file, not both" >&2; exit 1; }
     [[ "$PROMPT_FILE" == /* ]] || PROMPT_FILE="$(pwd)/$PROMPT_FILE"
     [[ -f "$PROMPT_FILE" && -r "$PROMPT_FILE" ]] || { echo "submit: cannot read --prompt-file $PROMPT_FILE" >&2; exit 1; }
+    [[ -s "$PROMPT_FILE" ]] || { echo "submit: --prompt-file $PROMPT_FILE is empty" >&2; exit 1; }
     PROMPT="$(<"$PROMPT_FILE")"
   fi
   [[ -n "$PROMPT" || -n "$PROMPT_FILE" ]] || { echo "submit requires --prompt or --prompt-file" >&2; exit 1; }
diff --git a/tests/test_issue36_prompt_transport.py b/tests/test_issue36_prompt_transport.py
index 7ee73be..134ba14 100644
--- a/tests/test_issue36_prompt_transport.py
+++ b/tests/test_issue36_prompt_transport.py
@@ -276,6 +276,44 @@ def test_s4_an_exec_error_is_a_failed_submit(runner, tmp_path, monkeypatch, caps
     assert _prompt_leftovers(tmp_path) == []
 
 
+def test_s4c_a_prompt_file_that_cannot_be_written_is_a_failed_submit(runner, tmp_path, monkeypatch, capsys):
+    """Merge review H1: the write, not only the exec, can fail (ENOSPC, EFBIG).
+    The runner must report it like an exec error and leave no partial file."""
+    lr, r = runner
+    real = lr.tempfile.NamedTemporaryFile
+
+    class _Broken:
+        def __init__(self, *a, **k):
+            self._fh = real(*a, **k)
+            self.name = self._fh.name
+        def __enter__(self):
+            self._fh.__enter__()
+            return self
+        def __exit__(self, *exc):
+            return self._fh.__exit__(*exc)
+        def write(self, _):
+            raise OSError(errno.ENOSPC, "No space left on device")
+
+    monkeypatch.setattr(lr.tempfile, "NamedTemporaryFile", _Broken)
+    ran = []
+    monkeypatch.setattr(lr.subprocess, "run", lambda *a, **k: ran.append(a) or None)
+    assert r.delegate_job("c", "claude", "Worker", "p" * 1000) is None
+    err = capsys.readouterr().err
+    assert "submit failed (exit 126)" in err and "cannot write the prompt file" in err, err
+    assert "Traceback" not in err
+    assert ran == [], "the wrapper must not be started without a prompt file"
+    assert _prompt_leftovers(tmp_path) == []
+
+
+def test_s1e_an_empty_prompt_file_is_refused(tmp_path):
+    """Merge review H3: --prompt-file with nothing in it registered an empty job."""
+    reg = tmp_path / "jobs"
+    empty = tmp_path / "empty.md"
+    empty.write_text("")
+    res = _dry_submit(tmp_path, reg, "--prompt-file", str(empty))
+    assert res.returncode != 0 and "is empty" in res.stderr, res.stdout + res.stderr
+
+
 def test_s4b_an_exec_error_on_the_busy_retry_is_reported_not_raised(runner, tmp_path, monkeypatch, capsys):
     lr, r = runner
     calls = []
@@ -599,7 +637,10 @@ def test_s9_shell_loop_removes_a_partial_prompt_file_and_says_why(tmp_path):
                        'output=$(delegate_job_safe submit --prompt "$(cat input.md)")\n')
     result = subprocess.run(["bash", str(harness)], cwd=tmp_path, capture_output=True, text=True, timeout=60)
     assert result.returncode != 0
-    assert "File too large" in result.stderr
+    if sys.platform == "linux":
+        # bash's own wording for EFBIG; macOS bash 3.2 prints nothing here
+        # (merge review N1), so only the portable line below is the contract
+        assert "File too large" in result.stderr
     leftovers = list((tmp_path / ".mam").glob("prompt-shloop-*"))
     assert not leftovers, [(p.name, p.stat().st_size) for p in leftovers]
     assert "delegate_job_safe: cannot write the prompt file" in result.stderr