ExitCode + finalization execution + Halt semantics (unblocks the erroru test family)

• Type: feature (Track A core — Halt lowering, program epilogue, init/final ordering; the ExitCode symbol itself could live in builtinheap once the codegen reads it)
• Status: backlog
• Opened: 2026-07-14
• Found by: Track B FPC-conformance burn-down. Filed under A because every piece is codegen/parser, not RTL surface.

What FPC does (and the testsuite's erroru.pp depends on, in order)

1. ExitCode: Longint is a writable global in System scope.
2. Halt(n) sets ExitCode := n, then runs unit finalization sections (reverse init order), then terminates with ExitCode.
3. Halt (no arg) = terminate with current ExitCode; normal program end also exits with ExitCode.
4. A finalization section may WRITE ExitCode (erroru's error_unit_exit checks the recorded exit code against the accepted/required error number and then zeroes it, turning an expected halt(100) into process exit 0 — that is how every accept_error/require_error test passes).

pxx today

• No ExitCode symbol at all (pascal26: undefined variable (exitcode)).
• initialization sections compile into __init_<unit> procs and run before main (ParseInitializationSection, parser.inc); finalization bodies are token-skipped and never executed ({ 'finalization' + its body are skipped }).
• Halt(n) lowers straight to the exit syscall — no finalization pass.

Scope sketch

• Parse finalization like initialization into __fini_<unit> procs; run them reverse-order from a common exit stub.
• Route Halt(n) / Halt / falling-off-main through that stub: store n (if given) to ExitCode, run finis, exit(ExitCode). Guard against recursive Halt from inside a finalization (FPC keeps going with the new code).
• erroru.pp additionally wants erroraddr: Pointer (nil-able) and GetFPCHeapStatus/TFPCHeapstatus — stub-able, but out of scope here; the finalization/ExitCode machinery is the load-bearing part.

Unblocks (conformance skip list)

tstring2.pp, tstring5.pp, texception3.pp, tobject1.pp (partly — also needs constructor fail), and every future erroru-using test the curated categories pick up.