fix(issue-36): the loop passes every delegated prompt as a file; a wrapper that cannot start is a failed submit, on the first try and on the retry

delegate_job writes the prompt to a temp file under the control root's .mam/
and hands the wrapper --prompt-file; the file is removed once the wrapper
returns. An OSError from starting the wrapper becomes a failed submit (rc 126)
that the existing error branch logs, so the session-busy retry no longer
dereferences a missing result. A retry that yields no job id, and a
compliance job that cannot be registered, are now logged instead of silent.

The collector caps are documented as the size of the evidence a reviewer is
shown; delivery has no cap of its own any more. The loop skill notes that a
pipeline hides the loop's exit code.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.agents/skills/multi-agent-mux-loop/scripts/diff_collect.sh

@@ -6,6 +6,9 @@ MAM_DIFF_UNAVAILABLE_MARKER="!!! CHANGE SET UNAVAILABLE !!!"
 MAM_DIFF_TRUNCATED_MARKER="!!! DIFF TRUNCATED !!!"
 MAM_DIFF_NESTED_MARKER="!!! NOT EXPANDED IN THIS DIFF !!!"
 
+# These caps bound the evidence a reviewer is shown, nothing else. The prompt
+# reaches the agent by file (Issue #36), so delivery has no size cap of its own:
+# only a diff over these limits is truncated (and marked).
 MAM_DIFF_MAX_BYTES="${MAM_DIFF_MAX_BYTES:-200000}"
 MAM_DIFF_MAX_LINES="${MAM_DIFF_MAX_LINES:-4000}"