exit-pre-sidecar

exit_pre sidecar

bpy.app.handlers.exit_pre writes $BDT_SMOKE_SIDECAR as Blender dies. Witnesses drivers-and-app-handlers. main does not write the file. The host runner asserts it after the process exits (tests/smoke/run_example.py --expect-sidecar).

No gallery still. There is no geometry: the witness is a file that does not exist until the process is already gone, and a render would look identical whether the handler fired or not.

The contract

exit_pre is the only handler in bpy.app.handlers that runs during interpreter teardown, and it is the difference between a callback that runs and one that silently never does. Code that relies on atexit for this — saving a session log, flushing a render manifest, releasing a licence token — is the class of bug this example exists to catch.

Blender	hasattr(bpy.app.handlers, "exit_pre")
4.5.11 LTS	False — AttributeError on access
5.1.2	True
5.2.1 LTS	True

Re-verified 2026-09-22 against all three binaries. exit_pre is also the only exit- or quit-related name in bpy.app.handlers on the versions that have it, so there is no older spelling to fall back to.

API reference: bpy.app.handlers (5.2 LTS) · bpy.app.handlers (4.5 LTS) — the 4.5 page lists no exit_pre, which is the absence this example turns into a skip.

Why 4.5 skips rather than fails

Exiting 77 on 4.5 is correct by design, not a gap in coverage. The handler does not exist there, so there is no contract to witness and no assertion that could meaningfully run. The catalog carries min_version 5.1 and the runner treats a skip above that floor as a FAIL, so the skip cannot quietly spread to a version that should run. tests/smoke/summarize.py makes a job red if every example skipped, so a repo-wide skip cannot pass either.

--force-run bypasses the skip so 4.5 proves the absence rather than assuming it: the run exits 2 on AttributeError, and also exits 2 if exit_pre turns out to exist on a version that should not have it.

Falsifiers

The harness checks the sidecar's contents (sidecar_contains=exit_pre-ok), not merely that a file appeared. Most falsifiers therefore exit 0 from the script — Blender reports success — and the harness fails afterwards, which is the only place a post-exit contract can be falsified.

Flag	What it breaks	Script exit	Harness
--no-handler	nothing registered, nothing written	0	FAIL, no sidecar
--silent-handler	exit_pre registered but writes nothing	0	FAIL, no sidecar
--wrong-text	handler writes nope	0	FAIL, contents mismatch
--write-in-main	from-main written in main, no handler	0	FAIL, contents mismatch
--atexit-instead	atexit writes atexit-ok instead of exit_pre	0	FAIL, contents mismatch
--force-run on 4.5	asserts exit_pre is genuinely absent	2	n/a

--write-in-main and --atexit-instead are the two that matter: both produce a file, so an existence-only check would pass them. They are why the catalog row carries sidecar_contains.

Run

Via the harness (sets $BDT_SMOKE_SIDECAR):

python tests/smoke/run_example.py --name exit-pre-sidecar \
  --blender blender --script examples/exit-pre-sidecar/exit_pre_sidecar.py \
  --series 5.2 --min-version 5.1 \
  --expect-sidecar /tmp/exit-pre.sidecar --sidecar-contains exit_pre-ok

Append -- --wrong-text (or any flag above) to falsify.

Exit codes

Per-script sequential checks. 9 is a valid check code; there is no rule against it. 77 is the smoke skip protocol, not a product check.

Code	Meaning
0	Success (including --silent-handler / --no-handler / --wrong-text / --write-in-main / --atexit-instead, which the harness then fails)
1	Uncaught exception (FATAL wrapper); also $BDT_SMOKE_SIDECAR unset
2	argparse / usage; also --force-run on Blender < 5.1 (exit_pre missing or unexpectedly present)
77	SMOKE_SKIP: exit_pre requires Blender 5.1+

The blender-smoke workflow runs the check on Blender 5.2 LTS (5.1 on the weekly cron, the needs-5.1 PR label, or manual dispatch) and skips on 4.5 LTS. Smoke does not pass the falsifier flags.