fix: exec() node fallback + feat: includeNodeShims option (fixes #64, #63)

[aayushprsingh]

Changes

fix: exec() falls back to node when sh is unavailable (fixes #64)

File: packages/core/src/kernel/kernel.ts

exec() currently throws "No shell available" when only createNodeRuntime() is mounted, because NodeRuntime registers 'node', not 'sh'. This breaks the README example immediately.

Fix: Added a fallback path — when 'sh' is not registered but 'node' is, exec() parses the command string, strips the 'node' prefix, and spawns node directly.

Now works out-of-the-box:
kernel.exec("node -e "console.log('hello')"") // ✓ instead of throwing

Changes:

• #parseCommandArgs(): shell-like arg tokenizer (handles '...', "...", escapes)
• #collectExecResult(): extracted shared stdout/stderr collection logic
• 3 new tests in packages/core/test/kernel/kernel-integration.test.ts

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feat: add includeNodeShims option (fixes #63)

Files: packages/nodejs/src/kernel-runtime.ts, packages/nodejs/src/driver.ts, packages/nodejs/src/execution-driver.ts, packages/nodejs/test/kernel-runtime.test.ts

Adds ability to disable Node.js polyfill shims (fs, http, process, Buffer, etc.) on globalThis. Useful for AI agents that need a clean global scope.

Usage:
// Clean scope: globalThis has NO injected shims
const driver = createNodeRuntime({ includeNodeShims: false });
await kernel.mount(driver);
// globalThis.fs === undefined ✓
// require('fs') still works via bridge permissions

Default: true (existing behavior unchanged).

Technical: buildFullBridgeCode() is keyed by includeNodeShims in a Map<boolean,string> cache. Each driver's bridge code is built once in the constructor.

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Tests

Both changes include tests — 3 for the exec() fallback, 3 for includeNodeShims.

[aayushprsingh]

Hey! Ran into issue #64 when trying the README example — kernel.exec('node -e "console.log(1)"') throws immediately because createNodeRuntime() registers 'node', not 'sh'.

This PR adds a fallback: when sh isn't registered but node is, we parse the command string, strip the node prefix, and spawn node directly. Also extracted #collectExecResult() to avoid duplication between the two paths, and added a shell-like arg tokenizer for the node fallback.

Happy to iterate if you'd like a different approach — e.g. if you'd prefer to just improve the error message rather than auto-fallback. Let me know!