Propagate post-process container exit code

[simone-stacks]

Summary

• cmd_post_process now propagates the post-process container's exit code instead of always returning success.
• Harvest still runs unconditionally, so a crashed agent's in-flight commits are still recovered onto the local branch (best-effort).
• On a non-zero exit, it warns that harvested commits may be partial state and returns the container's code.
• Gives callers (CI workflows, daemons) a real signal to gate publish on, so partial state doesn't ship.

Changes

• launch.sh: In cmd_post_process, capture docker inspect -f '{{.State.ExitCode}}' "$NAME" before harvest (falling back to 1 if inspect fails). Harvest still runs unconditionally; afterward, if the code is non-zero, log a warning to stderr and return "$exit_code". Previously the function swallowed the failure and returned success.
• tests/test_launch.sh: Add section "42. cmd_post_process propagates container exit code", asserting the function captures State.ExitCode and returns $exit_code on failure. Documents the partial-output recovery contract (harvest runs, but the failure propagates).

Self-review checklist

• This PR addresses a single concern (why?). If it covers multiple independent changes, I've split them into separate PRs.

Test plan

• ./tests/test.sh --unit — 1357 tests pass, 0 failed (test_launch.sh: 223).
• ./tests/test.sh --all — full integration matrix (Docker + API key); run in CI.
• Behavior: a post-process container exiting non-zero causes cmd_post_process to harvest, warn on stderr, then return that exit code; a clean exit returns 0 as before.

[moodmosaic]

container exit	harvest exit	process exit	note
0	0	0	clean — unchanged
2	0	2	the PR's goal ✓
0	1	1	harvest failure still propagates (not masked) ✓
3	1	1	set -e aborts at the harvest line; harvest's code wins

The only behavioral change vs. the old code is exactly the intended one (row 2: container fails + harvest succeeds now propagates the container's code). Everything else is unchanged. Good, tight change. Thank you! 👍

[moodmosaic]

Released as 0.21.1.