Self-host M3 Batch A: Runtime bootstrap real lowering for runtime-compile smoke

[PurHur]

Problem

M3 emit-TU execution (#2442) and the runtime-compile smoke path both depend on real Runtime bootstrap lowering (ctor/initVmContext/loadJit/parse/compile entry). Today this area is still partially stubbed/denied behind the M3 allowlist tracker (#1768) and can still trip Zend fallback or startup crashes when exercised by emit-TU helpers.

This issue scopes Batch A (Runtime bootstrap) as a gate-driven slice so M3 can move from emit_path=zend partial toward emit_path=native.

Gate / repro

Harness-safe Docker (LLVM 9):

./script/docker-exec.sh -- bash -lc '
  source script/php-env.sh
  script/apply-patches.sh
  BOOTSTRAP_M3_RUNTIME_COMPILE=1 make bootstrap-selfhost-runtime-compile-smoke
'

Scope (files / symbols)

• lib/Runtime.php
  • __construct path used by runtime-compile mode
  • compile entrypoints used by M3 drivers
• lib/JIT.php
  • compileRuntimeCtorM3Native
  • compileRuntimeInitVmContextM3Native (calls RuntimeInitVmContext::emit)
  • compileRuntimeLoadJitM3Native and any minimal helpers required by the runtime-compile smoke
• lib/JIT/RuntimeInitVmContext.php
  • initialization completeness (ties directly to Self-host M3: VM\Context native object allocation — complete C-floor for Runtime::initVmContext #2513)

Done when

• BOOTSTRAP_M3_RUNTIME_COMPILE=1 make bootstrap-selfhost-runtime-compile-smoke exits 0 on php-compiler:22.04-dev
• The runtime-compile smoke path does not rely on Zend bin/compile.php fallback to proceed
• Remaining unavoidable stubs are explicitly tracked under M2/M5: Retire PHP_COMPILER_SELFHOST_AOT stubs on Compiler compile spine #1520 (stub retirement) and/or Self-host M3: compile-driver real lowering symbol batch tracker #1768 (allowlist batches)

Links / dependencies

• Parent batch tracker: Self-host M3: compile-driver real lowering symbol batch tracker #1768 (Batch A)
• Epic: Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492
• Blocked by / paired with: Self-host M3: VM\Context native object allocation — complete C-floor for Runtime::initVmContext #2513 (VM\Context allocation), Self-host M3: native emit-TU binaries run without startup crash #2442 (emit-TU execute)
• Related umbrella: M2/M5: Retire PHP_COMPILER_SELFHOST_AOT stubs on Compiler compile spine #1520 (stub retirement on compile spine)

[PurHur]

Landed in #2549 (merged): thin native Runtime::parseandcompile* LLVM on emit-TU link + bridge routing; integrated with #2540 emit-TU spine (RuntimeEmitTuAlloc, block-ptr stubs). Emit-helper link green; emit_path=native still blocked on parser spine real lowering.