codegen: captured let loses its TDZ on the second loop iteration

[proggeramlug]

Independent reproducer

This is a synchronous language-semantics bug, not an application/Bun API dependency.
The source below runs without a bundle, credentials, network, or the generator fix.

function test() {
  const results: string[] = [];
  for (let index = 0; index < 2; index++) {
    let read = () => value;
    try { read(); results.push('missing-tdz'); }
    catch (error) { results.push(error instanceof ReferenceError ? 'tdz' : 'wrong-error'); }
    let value: number;
    results.push(String(read()));
    value = index;
    results.push(String(read()));
    let recurse = (n: number): number => n === 0 ? value : recurse(n - 1);
    results.push(String(recurse(2)));
  }
  return results.join(',');
}
console.log(test());

Pinned Node 26.5.1 prints:
tdz,undefined,0,0,tdz,undefined,1,1

Perry prints:
tdz,undefined,0,0,missing-tdz,undefined,1,1

The second iteration's read before the let declaration must throw ReferenceError.
The no-initializer declaration must then end that iteration's TDZ with undefined.

Before/after evidence

macOS arm64, Wasm host enabled, compact GC (RS4GC=0, shadow stack=1,
inline shadow slot=0, full outline IC=1), auto-optimization disabled.
Every case uses a frozen compiler and all nine coherent provider archives from
its exact source commit, not mixed libraries or source-stamp overrides.

Identical failure at both O0 and Oz on all three trees:

• main 53df2c671fff33b1f8f624432372c2401db8b1d0 (0.5.1530);
• f3e8d5d1a66753cb00d15da552ad73abb8740520, main 603b074ac
  plus unrelated fix(child_process): finish output readers after EOF and spawn failure #10042/fix(runtime): honor AsyncResource.bind and other own function overrides #10046 compatibility fixes;
• 81b47b47cace5b150edde32059ff272a3a19eca5, main 603b074ac
  plus the missing ordinary-boxed-declaration-cell fix in fix(codegen): initialize missing cells in reused boxed declarations #10049.

Thus this is not introduced by #10049. Its initial broad control fixture exposed
the existing bug. The separate generator callback reproduction now passes.

Example native compile (with a matched build's runtime directory configured):
PERRY_LL_OPT_LEVEL=0 perry compile tdz-loop.ts -o tdz-loop --platform bun --enable-wasm-runtime --no-auto-optimize
Use fresh output/cache paths and run under a 15-second timeout.

Implementation scope / acceptance

• Preserve per-iteration lexical binding identity and reestablish TDZ on every
  block entry; do not reset shared var bindings or reuse a previous iteration's cell.
• Audit TDZ box preallocation and loop capture/freshening paths. The precise
  responsible lowering path has not yet been isolated; this issue is behavioral evidence.
• Add a byte-for-byte Node/native gap regression, then cover retained callbacks,
  initialized and uninitialized let, const, recursion, and shared var controls.
• Verify O0/Os/Oz under default and compact GC. No application rebuild is required.

Local evidence: tdz-loop-before-after-20260911.log and the six-case result
record /var/folders/8v/09vl257j2_v70v2k77gh01n00000gn/T/perry-tdz-loop-ab-szGh6Q/result.json.

[proggeramlug]

Fixed by merge train 186r (#10247) at eb13fa1.