feat(instrument): Add --stub-wasi flag to replace WASI imports with stubs

[shogochiai]

Problem

When using ic-wasm instrument on a canister WASM compiled with Emscripten, the resulting instrumented WASM contains WASI imports that IC rejects at install time:

Error: Wasm module has an invalid import section.
Module imports function 'fd_close' from 'wasi_snapshot_preview1'
that is not exported by the runtime.

Use Case

For languages that compile through Emscripten/C (e.g., Idris2), WASI imports are introduced by the toolchain, not by user code. This flag provides a practical workaround until native WASM backends become available.

Solution

Add --stub-wasi flag to the instrument subcommand that replaces WASI imports with local stub functions:

WASI Function	Stub Behavior
fd_close	Returns 0 (success)
fd_write	Writes 0 to nwritten, returns 0
fd_read	Writes 0 to nread, returns 0
fd_seek	Writes 0 to newoffset, returns 0
environ_sizes_get	Writes 0 to both params, returns 0
environ_get	Returns 0
proc_exit	Traps (unreachable)
Others	Returns 0

Usage

ic-wasm canister.wasm -o instrumented.wasm instrument --stub-wasi

⚠️ Important Note

This is a workaround for edge cases (Emscripten, wasi-sdk).

The recommended approach is to build without WASI imports:

• Rust: Use wasm32-unknown-unknown target with ic-cdk
• C/C++: Configure toolchain to avoid WASI dependencies

Stub functions return success (0), which may hide real failures if your code actually depends on WASI functionality.

Test plan

• Added stub_wasi test that verifies WASI imports are removed
• All existing tests pass
• cargo clippy and cargo fmt pass

🤖 Generated with Claude Code

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