👷 Fix @effectionx/inline wasm plugin build

[taras]

Motivation

CI is red at the Build step on PRs (e.g. #218) — not in tests. The failure
is @effectionx/inline#build:bundle (exit 101): compiling swc-plugin-inline
to wasm32-wasip1 fails to link under current Rust:

rust-lld: error: undefined symbol: __emit_diagnostics
rust-lld: error: undefined symbol: __set_transform_result
rust-lld: error: undefined symbol: __add_leading_comment_proxy
…

Those __* / *_proxy symbols are the SWC host ABI functions an SWC wasm
plugin imports from its runtime host — they are meant to stay as undefined
imports in the .wasm. Newer rust-lld/wasm-ld no longer leaves undefined
symbols as imports by default, so the release link errors.

There were actually two problems:

1. The link needs -C link-arg=--allow-undefined to keep the host-ABI symbols
   as imports.
2. The crate's cargo config (inline/swc/.cargo/config.toml) was never being
   applied. build:bundle runs cargo from inline/
   (cargo build --manifest-path swc/Cargo.toml …), and cargo discovers
   .cargo/config.toml relative to the working directory, not the manifest.
   So the rustflags there — including the pre-existing --cfg=swc_ast_unknown —
   were silently ignored in CI.

Approach

Move the cargo config to the package root, inline/.cargo/config.toml, so it is
discovered from the directory build:bundle runs in, and add the
--allow-undefined link arg:

[target.'cfg(target_arch = "wasm32")']
rustflags = ["--cfg=swc_ast_unknown", "-C", "link-arg=--allow-undefined"]

This makes both the existing swc_ast_unknown cfg and the new link arg take
effect. A comment documents why the file must live at inline/.cargo rather than
next to the crate.

Verification (local)

• rustup stable 1.96.0 (newer than CI's toolchain) + wasm32-wasip1:
  • pnpm --filter @effectionx/inline run build:bundle — links cleanly, emits
    swc_plugin_inline.wasm. Reproduced the original failure first, then
    confirmed the fix via the exact CI invocation.
  • pnpm build — full tsc --build + turbo run build:bundle green.
  • node --env-file=.env --test "inline/*.test.ts" — 32/32 pass, including
    swc.test.ts, which loads and runs the built wasm plugin.

Scoped entirely to inline/; no workflow or other-package changes. Unblocks the
Build step on #218.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: 956d804d-dbed-4b80-bde5-eaade67880e2

📥 Commits

Reviewing files that changed from the base of the PR and between 6982b1c and 22f4162.

📒 Files selected for processing (2)

• inline/.cargo/config.toml
• inline/swc/.cargo/config.toml

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/inline-swc-wasm-build

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[pkg-pr-new]

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npm i https://pkg.pr.new/@effectionx/inline@219

commit: 22f4162