Compiler Pipeline (codegen + compile + symtable + flowgraph + assemble) | 6 FIX

codegen.c (6,632 lines) — 4 FIX

1. NULL deref + ref leak in codegen_setup_annotations_scope (line 716-720): PyLong_FromLong result not NULL-checked, passed to ADDOP_LOAD_CONST which dereferences it. Also never DECREF'd even on success.
2. Ref leak of mangled in codegen_nameop (line 3280): RETURN_IF_ERROR(scope) early-returns without DECREF'ing mangled from _PyCompile_MaybeMangle.
3. Unchecked _PyCompile_PushFBlock in codegen_unwind_fblock_stack (line 669): Return value silently discarded, error lost, frame block stack left inconsistent.

compile.c (1,772 lines) — 1 FIX

1. Ref leak of orig in _PyCompile_TweakInlinedComprehensionScopes (line 1096-1114): PyDict_GetItemRef returns new ref in orig, never DECREF'd on any path (success or error). Leaks on every inlined comprehension.

assemble.c (802 lines) — 1 FIX

1. assemble_emit_instr returns ERROR without exception (line 420-421): Bytecode overflow check returns ERROR without PyErr_NoMemory() → SystemError.

symtable.c (3,355 lines) — 0 FIX (clean)

flowgraph.c (4,088 lines) — 0 FIX (clean)

Did not fix

1. Ref leak of mangled in codegen_deferred_annotations_body (line 792-818)
   • I do not see a simple way to fix this without overhauling the macros (ADDOP* & VISIT) that can early return

• Issue: Umbrella issue: bugs found using cpython-review-toolkit #146102