feat(codegen): #225 PR3c — WasmGC CPS transform, Async→Async chaining

[hyperpolymath]

#225 PR 3c — WasmGC CPS transform: Async→Async chaining

A continuation may itself be an async boundary; Thenables now compose up the call chain. The transform is reachable from the ExprLambda continuation-body site via a forward-ref hook (async_transform_hook, set at module init — avoids relocating the transform into the gen_expr rec group) so it re-applies recursively. detect_async_base_case gains ~extra (live locals capturable at the call site, incl. the outer binder/captures for a recursively-transformed inner continuation); the single-boundary rejection on cont is dropped. Recursion terminates (each step peels one boundary off a strictly-smaller finite continuation).

Three further root-cause fixes (all surfaced by the first-ever nested lambda)

1. find_free_vars ExprBlock used the original bound_vars for the tail expr, not the stmt-threaded set → block-local lets reported free → detect spuriously rejected chains. Now threads bound_after.
2. Nested lambda_id reuse — next_lambda_id bumped only after body-gen; now advanced before.
3. Lost nested lambda + wrong dispatch — ExprLambda rebuilt the result ctx from pre-body ctx_after_env (discarding the nested lambda/types/globals), and the closure stored the pre-reserved id while the element segment maps table slot = lambda list position. Now post-body module state is threaded forward (enclosing locals kept) and the closure stores the lambda's append position (= table slot), correct under any nesting order.

All three were invisible before PR3c (no nested lambdas had ever existed in generated code). Consistent with the PR2/PR3 pattern: the #199 path had only ever been static-verified.

Verification

New e2e tests/codegen/http_cps_chain.{affine,mjs}: 2-hop chain — launch → req A → outer continuation issues req B → inner continuation combines s1(=200, A-derived) with B status(=201) ⇒ 200201; A issued synchronously, B deferred to the continuation. Full tools/run_codegen_wasm_tests.sh green (PR2 base + PR3a capture + PR1 skeleton, no regression); dune test --force 260 green.

Conforms to typed-wasm ADR-005 (accessor model). Slice 3 of former PR3. Refs #225 #160 (NOT Closes — joint-close is the final #225 PR).

🤖 Generated with Claude Code

[github-actions]

🔍 Hypatia Security Scan

Findings: 44 issues detected

Severity	Count
🔴 Critical	12
🟠 High	21
🟡 Medium	11

⚠️ Action Required: Critical security issues found!

View findings

[
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    "type": "banned",
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    "severity": "high"
  },
  {
    "reason": "Superseded by 0-AI-MANIFEST.a2ml",
    "type": "banned",
    "file": "AI.djot",
    "action": "delete",
    "rule_module": "root_hygiene",
    "severity": "high"
  },
  {
    "reason": "Issue in quality.yml",
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    "action": "create",
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    "severity": "high"
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  {
    "reason": "Issue in security-policy.yml",
    "type": "missing_workflow",
    "file": "security-policy.yml",
    "action": "create",
    "rule_module": "workflow_audit",
    "severity": "medium"
  },
  {
    "reason": "Action hyperpolymath/standards/.github/workflows/governance-reusable.yml@main needs attention",
    "type": "unpinned_action",
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    "action": "pin_sha",
    "rule_module": "workflow_audit",
    "severity": "high"
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  {
    "reason": "TypeScript file detected -- banned language",
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    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/example/smoke_driver.ts",
    "action": "flag",
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    "severity": "critical"
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  {
    "reason": "TypeScript file detected -- banned language",
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    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/cli.ts",
    "action": "flag",
    "rule_module": "cicd_rules",
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  {
    "reason": "TypeScript file detected -- banned language",
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    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/mod.ts",
    "action": "flag",
    "rule_module": "cicd_rules",
    "severity": "critical"
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  {
    "reason": "TypeScript file detected -- banned language",
    "type": "banned_language_file",
    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/lib/compile.ts",
    "action": "flag",
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    "severity": "critical"
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  {
    "reason": "TypeScript file detected -- banned language",
    "type": "banned_language_file",
    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/lib/runner.ts",
    "action": "flag",
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