feat: witness exit_pre via post-exit sidecar

[TMHSDigital]

Summary

• examples/exit-pre-sidecar/: bpy.app.handlers.exit_pre writes `` as Blender dies. main does not write the file.
• Catalog runner now forwards expect_sidecar / sidecar_contains (was canary-only). Without that, CI would have been a vacuous PASS.
• 4.5 SKIP via min_version 5.1. No gallery still.

Type

• feat — new skill / rule / snippet / template / example (minor bump)

Squash-merge subject: feat: witness exit_pre via post-exit sidecar

Evidence

Harness contents vs existence — live-run-proven

sidecar_ok in tests/smoke/protocol.py checks existence, non-empty, and optional substring. Catalog row: sidecar_contains: exit_pre-ok.

Flag	Harness	File
(none)	[PASS]	exit_pre-ok
--silent-handler	[FAIL] missing post-exit sidecar	absent
--no-handler	[FAIL] missing post-exit sidecar	absent
--wrong-text	[FAIL] sidecar missing expected text 'exit_pre-ok'	nope
--write-in-main	[FAIL] sidecar missing expected text 'exit_pre-ok'	from-main
--atexit-instead	harness exit 1	atexit-ok (existence-only would have been a false pass)

--no-handler proves main does not write the sidecar. --write-in-main / --atexit-instead prove the content check, so a clean-exit write that is not exit_pre is red.

Binaries: Win .scratch/blender-5.2.1-windows-x64/blender.exe 5.2.1 LTS 9e2066aef7ef; blender-5.1.2-windows-x64 5.1.2 ec6e62d40fa9; blender-4.5.11-windows-x64 4.5.11 LTS 4db51e9d1e1e.

Skip / force-run — live-run-proven

Run	Result
5.2 / 5.1 harness --min-version 5.1 --expect-sidecar	[PASS]
4.5 harness --series 4.5 --min-version 5.1	[SKIP] exit_pre requires Blender 5.1+ (no sidecar required)
4.5 harness, no min_version	[FAIL] skipped with no --min-version (unexpected)
4.5 --force-run (direct blender)	exit 2, AttributeError: 'bpy.app.handlers' object has no attribute 'exit_pre'

Gallery

None. No geometry.

Backlog (ROADMAP, not this PR's code beyond the bullet)

Falsification flags for Phases 6–9 were local-Windows only. Alongside inverted-canary marker-text.

Release-owned fields — do not hand-edit

Left at 0.51.0.

Test plan

• 5.2 smoke: exit-pre-sidecar PASS (sidecar asserted)
• 4.5 smoke: exit-pre-sidecar SKIP with reason, counted separately
• validate-counts / manifest: 50 examples
• Socket not pending/failing
• After squash-merge: quote release.yml on the merge SHA; expect RELEASE (bump=minor) → v0.52.0

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