async labeled switch with await spins forever at break label #9186

Release blocker

Full-tier CI run 33317606566 timed out in cargo-test-perry (8/8) after 120 minutes. The exact stuck test is:

issue_5868_switch_state_machine::labeled_switch_break_label

The test reached break l after its awaited console.log, then the generated binary consumed CPU indefinitely. The seven other Perry integration shards passed.

Minimal repro

async function run() {
  l: switch (1) {
    case 1:
      console.log(await Promise.resolve("in-case"));
      break l;
    case 2:
      console.log("no");
  }
  console.log("after");
}
run();

Expected:

in-case
after

Actual: generated binary spins forever.

Root-cause evidence

HIR tracing on release candidate 7f1ae8b33ad971460502bd3c127d2820a7762650 shows state 4 still contains LabeledBreak("l"). Source lowering represents a labeled non-loop statement as a labeled run-once do ... while(false). Generator linearization drops that label wrapper while linearizing its yielding loop, but rewrite_labeled_bc_in_stmts deliberately does not rewrite a targeted labeled break inside a nested switch. The later yielding-switch desugar therefore preserves an unresolved labeled break, and state-machine codegen falls back to the dispatch loop target and spins.

Acceptance criteria

• The existing labeled_switch_break_label integration test completes with in-case\nafter\n.
• Post-transform HIR no longer leaves the source LabeledBreak("l") unresolved in the async dispatch states.
• Preserve switch-local break behavior and outer-label break behavior when a yielding switch is nested in a labeled loop/run-once wrapper.
• The full Perry integration shard 8 completes within its CI budget.