release blocker: test_gap_gc_alloc_point_no_move compile does not terminate #8913

Release evidence

One fixture deterministically consumes multiple Full CI jobs until their hard limits: test-files/test_gap_gc_alloc_point_no_move.ts.

• Candidate: 7c9f6016987ea9fdce2d253fb8666428cf0c6d24
• Full CI: https://github.com/PerryTS/perry/actions/runs/33123474583

Three independent consumers identify it:

• gap-suite shard 1 passed 37/73 tests, then emitted no result for test 38 for about 75 minutes and was killed at its 110-minute limit:
  https://github.com/PerryTS/perry/actions/runs/33123474583/job/98695927559
• parity shard 10 passed 37/115 tests, then emitted no result for test 38 for about 164 minutes and was killed at its 210-minute limit:
  https://github.com/PerryTS/perry/actions/runs/33123474583/job/98698057058
• compile-smoke hit GitHub's default 360-minute limit. Its error artifact contains exactly one empty in-flight log, test_gap_gc_alloc_point_no_move.compile_error.log:
  https://github.com/PerryTS/perry/actions/runs/33123474583/job/98698056865

The candidate tree's round-robin selection confirms test 38 in both shards is test_gap_gc_alloc_point_no_move. The empty compile log and live perry process place the stall inside compilation, before an error is reported.

The candidate already contains the bounded TailCallElim alloca walk from #8894, so this is a remaining compile-time pathology.

Reproduction

cargo build --release
time target/release/perry \
  test-files/test_gap_gc_alloc_point_no_move.ts \
  -o /tmp/perry-gap-gc-alloc-point

./run_parity_tests.sh --filter test_gap_gc_alloc_point_no_move

Profile compiler passes during the isolated command; do not diagnose this by repeatedly running the entire Full CI matrix.

Required fix

Find and bound the compiler phase that scales pathologically on this fixture while preserving the fixture's allocation-point/no-move assertions. Add pass timing or a focused regression guard so a future unbounded walk fails close to the source.

Acceptance criteria

• The isolated compile completes reliably and well below the 110-minute shard limit on an ubuntu-latest-class runner.
• The fixture runs and passes; it is not skipped, weakened, or allowlisted.
• Full-mode gap shard 1 and parity shard 10 complete and upload reports.
• compile-smoke completes rather than reaching six hours.