feat: distinguish smoke skips from passes and assert post-exit sidecars

[TMHSDigital]

Summary

• Host runner tests/smoke/run_example.py + catalog tests/smoke/catalog.json + summarize.py.
• SKIP is exit 77 + SMOKE_SKIP: <reason> and only when --min-version is above this Blender. Exit 0 with that marker is FAIL (vacuous). Skip on a version that should run is FAIL. Zero PASSes is red (exit 2).
• Post-exit sidecar is opt-in (--expect-sidecar / $BDT_SMOKE_SIDECAR), asserted after Blender dies. No gallery still.
• No new shipped examples. Canaries live under tests/smoke/.

Today, before this PR (inspection)

blender-smoke.yml was 45 independent set -e steps. Exit 0 = green. There was no skip channel. run_smoke.py was pass-or-die then ALL SMOKE CHECKS PASSED. A 5.0-only example that sys.exit(0) on 4.5 would have been indistinguishable from a real pass.

Evidence

live-run-proven .scratch/blender-5.2.1-windows-x64/blender.exe Blender 5.2.1 LTS (9e2066aef7ef):

Probe	Wrapper exit	Notes
--min-version 99.0 + always-skip canary	0 [SKIP]	proc_exit 77
--min-version 4.0 + always-skip canary (should run)	1 [FAIL] skipped on 5.2 but min-version 4.0 (should run)	not a clean pass
sidecar written, --expect-sidecar after process death	0 [PASS]
--omit-sidecar + --expect-sidecar	1 missing post-exit sidecar
summarize 1 PASS + 1 SKIP	0
summarize all SKIP	2 every example skipped; job is not green

.scratch/blender-4.5.11-windows-x64/blender.exe Blender 4.5.11 LTS: expected skip wrapper exit 0 [SKIP].

python tests/smoke/test_harness.py -v — 16 tests OK (no Blender). Inverted canaries are also CI steps that assert wrapper exit 1.

run_smoke.py still green on 5.2.1: 12 passed, 0 skipped.

inspection-only: YAML splice, catalog listing matches plugin 45 example dirs.

Test plan

• validate-harness + validate counts/manifest/frontmatter
• blender-smoke 5.2 + 4.5: unit tests, red canaries (exit 1 asserted), expected SKIP in summary, sidecar PASS, catalog green
• Socket not pending
• squash feat: → release.yml RELEASE (expect v0.48.0)

[TMHSDigital]

CI canaries on PR head d71160c (run 34408788566):

live-run-proven (CI Linux portable)

• 5.2: /home/runner/work/_temp/bl/blender-5.2.1-linux-x64/blender Blender 5.2.1 LTS (9e2066aef7ef)
• 4.5: /home/runner/work/_temp/bl/blender-4.5.13-linux-x64/blender Blender 4.5.13 LTS (daeeeca98fb0)

Both legs:

• expected skip: [SKIP] canary-skip: harness canary (always skip) (wrapper 0; summary counts SKIP separately)
• unexpected skip: [FAIL] skipped on X.Y but min-version 4.0 (should run) then unexpected skip exited 1 (correct)
• sidecar: [PASS] canary-sidecar after process death
• missing sidecar: [FAIL] missing post-exit sidecar then missing sidecar exited 1 (correct)
• job summary: 47 passed, 1 skipped, 0 failed (canary-skip listed SKIP, not PASS)

First push (5cdd729) never got a smoke job: runner.temp is illegal in job-level env (actionlint). Fixed in d71160c.