Self-host M2: BootstrapVmDriver native execute smoke (post-#2134 bin/vm.php link)

[PurHur]

Problem

#2134 tracks native-linking bin/vm.php in compiler_lib_spine_smoke. #2134 prerequisite is now green (#2499 ✅): spine link passes; only bin/vm.php remains deferred in script/bootstrap-spine-deferred-lib.php.

Link-only proves the TU bundles; it does not prove the compiled VM driver can interpret PHP at runtime (-r 'echo 1;' or tiny fixture).

Without an execute smoke, M2 can show bundle OK while the VM entry mis-links or crashes on first opcode — blocking honest progress toward #1521 (Zend-free bin/vm.php).

Goal

After #2134 promotes real bin/vm.php:

1. script/bootstrap-selfhost-vm-driver-execute-probe.sh builds/runs spine-linked VM driver on a 1-line fixture
2. BOOTSTRAP_VM_DRIVER_EXECUTE_GATE=1 opt-in in ci-local.sh llvm group (CI: BOOTSTRAP_VM_DRIVER_EXECUTE_GATE default-on in ci-local after #2201 opt-in green #2227 default-on follow-up)
3. Expected stdout contains vm driver ok (or documented needle)

Implementation hints

Piece	Path	Notes
Probe (TBD)	script/bootstrap-selfhost-vm-driver-execute-probe.sh	Mirror bootstrap-selfhost-helloworld-probe.sh
Spine	test/selfhost/compiler_lib_spine_smoke/main.php	Real require_once of bin/vm.php
VM entry	bin/vm.php	Replace test/bootstrap-aot/vm_run_smoke.php
Env	script/ci-defaults.env	BOOTSTRAP_VM_DRIVER_EXECUTE_GATE="${...:-0}"
CI	script/ci-common.sh	ci_run_bootstrap_vm_driver_execute()
Docs	docs/bootstrap-selfhost.md, docs/self-host-target.md	M2 gate row

Bootstrap gates

Gate	Command	Blocker
M2 spine link	BOOTSTRAP_LIB_SPINE_SMOKE=1 make bootstrap-selfhost-lib-spine-smoke	#2134
VM spine -r	BOOTSTRAP_LIB_SPINE_VM_SMOKE=1 make bootstrap-selfhost-lib-spine-vm-smoke	partial today
VM driver execute	BOOTSTRAP_VM_DRIVER_EXECUTE_GATE=1 ./script/bootstrap-selfhost-vm-driver-execute-probe.sh	this issue
M3 emit (orthogonal)	make bootstrap-selfhost-helloworld	#2442

Done when

• Probe exits 0 on php-compiler:22.04-dev when Self-host M2: native-link bin/vm.php + lib/AOT/Linker.php in spine smoke #2134 link green
• Skip with clear message when LLVM missing
• No GitHub Actions — verify via make test-harness or ./script/docker-ci-local.sh

Repro (after #2134)

./script/docker-exec.sh -- bash -lc '
  script/apply-patches.sh
  BOOTSTRAP_VM_DRIVER_EXECUTE_GATE=1 ./script/bootstrap-selfhost-vm-driver-execute-probe.sh
'

Dependencies

• Self-host M2: native-link bin/vm.php + lib/AOT/Linker.php in spine smoke #2134 — native link bin/vm.php (blocker)
• Self-host M3: native emit-TU binaries run without startup crash #2442 / M3 emit TU: runtime spine skip-list + emit phase diagnostics (#2442) #2506 — M3 emit (orthogonal; do not block VM link work)

Links

• CI: BOOTSTRAP_VM_DRIVER_EXECUTE_GATE default-on in ci-local after #2201 opt-in green #2227 CI default-on ladder · Self-host M2: native-link 5 deferred spine inventory paths #2126 ✅
• Epic Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492