node: unflag wasm-modules (compat-backfill) + shadow-realm

[colinhacks]

Adds two feature-matrix rows so nub auto-injects the experimental flag on the Node versions that still require it.

wasm-modules (mechanical compat-backfill)

`importof.wasmfiles is **default-on in current Node** — the--experimental-wasm-modules` flag became a NoOp at 24.5.0 (24.x line) and 22.19.0 (22.x line) via nodejs/node#57038. Per the unflag-on-prior-versions rule (default-on in current Node ⇒ backfill it where it was flagged), this is a mechanical banded unflag, same shape as the live sqlite row.

Bands (injected where the flag both exists and is required):

[18.19, 22.19)  inject   # 22.x line, pre-backport
[22.19, 23.0)   native   # backport landed
[23.0,  24.5)   inject   # 23.x EOL before the backport — stays flagged
[24.5,  inf)    native   # default-on

The 23.x line never received the #57038 backport (EOL before 24.5), so it stays flagged through the end of the line — verified against .repos/node doc/api/esm.md.

Resolver passthrough: nub leaves .wasm import specifiers untouched. TRANSPILE_EXTS covers only .ts/.tsx/.mts/.cts/.jsx, and the additive resolver (resolveTs) returns null for a .wasm specifier, so it falls through to Node native wasm loader — no transform, no re-resolve.

shadow-realm

--experimental-shadow-realm exists from Node 18.13/19.0 (below the floor) and has never been made default-on through Node 26 (TC39 Stage 3, rides V8 --harmony-shadow-realm staging). Inject across the whole supported floor [18.19, inf), like vm-modules.

Important

shadow-realm is NOT the mechanical case wasm-modules is — it is a Stage-3, not-default-on-anywhere global, and turning it on by default is a product/posture call, not a backport. The thread .fray/v0x-shadow-realm-unflag.md recommends DEFER. It is included here per a coordinator-relayed decision, but a coordinator relay is not user authority — this row needs Colin own sign-off before merge. If the call is to defer, drop the shadow-realm commit/row and ship wasm-modules alone.

Tests

• Band tests in feature_matrix.rs (matrix layer) and end-to-end compute_inject_flags band tests in flags.rs (the spawn path) for both features.
• cargo test -p nub-core --lib → 274 passed; clippy + fmt clean.

https://claude.ai/code/session_01YRvztkcr4fzfg9rD5edUwa

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Project	Deployment	Actions	Updated (UTC)
nub	Ready	Preview, Comment	Jun 20, 2026 11:56pm

[Copilot]

Pull request overview

Adds new Node feature-matrix entries so Nub can auto-inject experimental flags on Node versions that still require them, and documents the resulting “Modern APIs” surface in the runtime docs.

Changes:

• Add wasm-modules version bands to inject --experimental-wasm-modules only where still required.
• Add shadow-realm entry to inject --experimental-shadow-realm across the supported floor, plus tests.
• Update runtime docs “Modern APIs” table with new rows for ShadowRealm and Wasm module imports.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
site/content/docs/runtime/index.mdx	Adds Modern APIs table rows for ShadowRealm and Wasm module imports.
crates/nub-core/src/node/flags.rs	Adds band/injection tests for wasm-modules and shadow-realm via compute_inject_flags.
crates/nub-core/src/node/feature_matrix.rs	Adds new feature-matrix rows + band tests for shadow-realm and wasm-modules.

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[colinhacks]

CI failure — do not merge

Test (macos-14, node 24) and Test (windows-latest, node 24) fail. Both on the same bug introduced by the shadow-realm row:

ERR_WORKER_INVALID_EXEC_ARGV: Initiated Worker with invalid execArgv flags: --harmony-shadow-realm

Root cause: --experimental-shadow-realm implies --harmony-shadow-realm internally. Node adds the implied V8 harmony flag to process.execArgv. The worker polyfill (runtime/worker-polyfill.mjs:120) passes process.execArgv directly to NodeWorker — Node 24 rejects --harmony-* flags in worker execArgv with ERR_WORKER_INVALID_EXEC_ARGV.

Failing tests: worker_transpiles_ts_entry, worker_message_roundtrip, worker_throw_surfaces_to_parent_onerror — all worker tests on Node 24.16.0.

Fix required in runtime/worker-polyfill.mjs (line 120): filter --harmony-* flags from execArgv before passing to NodeWorker:

execArgv: process.execArgv.filter(f => !f.startsWith('--harmony')),

This is the correct fix regardless — any harmony-implying flag injected by nub would trigger this. The filter is safe: harmony flags are V8 internals that Node documents as invalid for workers.

This fix should land before or with this PR. The wasm-modules row is clean; only shadow-realm triggers this.