fix: CLI fails to start on Windows with process.execve unavailable (#8)

## Related Issue

No linked issue — problem explained below.

## Problem

On Windows, `pythinker` installed via npm fails immediately:

```
Failed to start Pythinker Code: The feature process.execve is unavailable on the current platform, which is being used to run Node.js
```

Windows Node defines `process.execve` as a function that throws
`ERR_FEATURE_UNAVAILABLE_ON_PLATFORM` when called. The launcher's
existence check (`process.execve !== undefined`) therefore routed
Windows into the execve path and crashed before the existing spawn
fallback could run.

## What changed

The launcher checks the platform first: win32 always uses the spawn
fallback; the execve path (which preserves pid, process group, and
controlling terminal) remains for POSIX. Added a regression test that
fakes win32 with a throwing `execve` and asserts the fallback child
completes — verified it fails against the previous launcher.

## Checklist

- [x] I have read the
[CONTRIBUTING](https://github.com/Pythoughts-labs/pythinker-code/blob/main/CONTRIBUTING.md)
document.
- [x] I have linked a related issue, or explained the problem above.
- [x] I have added tests that prove my feature works.
- [x] Ran `gen-changesets` skill, or this PR needs no changeset.
- [x] Ran `gen-docs` skill, or this PR needs no doc update.

Author: elkaix

.agents/skills/gen-docs/SKILL.md

@@ -7,7 +7,7 @@ description: Update Pythinker Code CLI user documentation after meaningful code
 
 ## Overview
 
-This repository maintains English user documentation under `docs/`.
+This repository (`github.com/Pythoughts-labs/pythinker-code`) maintains English user documentation under `docs/`, published at **https://code.pythinker.com**.
 
 Use this skill to update the corresponding documentation whenever the codebase has changes that affect product behavior or user experience.
 
@@ -17,7 +17,7 @@ For a **full pre-release audit** of all pages (detecting hallucinations and cove
 
 This skill depends on the following being in place. If any are missing, stop and report to the user before continuing:
 
-- `docs/` directory with documentation pages and `docs/.vitepress/config.ts` set up (VitePress site).
+- `docs/` directory with documentation pages and `docs/.vitepress/config.ts` set up (VitePress site, deployed to code.pythinker.com).
 - `docs/AGENTS.md` style guide — defines terminology, typography, and writing style.
 
 ## Workflow

.agents/skills/sync-changelog/SKILL.md

@@ -15,7 +15,7 @@ apps/pythinker-code/CHANGELOG.md
 
 This file is the **only upstream source** for the documentation-site changelog. Internal package changelogs such as `packages/*/CHANGELOG.md` do not go into the documentation site.
 
-After the release flow finishes (Release PR merged → `Version Packages` completed → npm publish succeeded), maintainers manually run this skill to copy the new CLI changelog entries into the docs site.
+After the release flow finishes (Release PR merged → `Version Packages` completed → npm publish succeeded), maintainers manually run this skill to copy the new CLI changelog entries into the docs site (published at https://code.pythinker.com).
 
 ## When To Use
 
@@ -38,7 +38,7 @@ Core rule: the English docs changelog is the source of truth for user-facing rel
 
 Before editing, confirm:
 
-- The released version exists on npm (`npm view @pythoughts/pythinker-code versions --json`) or has a matching GitHub Release tag.
+- The released version exists on npm (`npm view @pythoughts/pythinker-code versions --json`) or has a matching GitHub Release tag on `Pythoughts-labs/pythinker-code`.
 - The top of `apps/pythinker-code/CHANGELOG.md` is that new version.
 - The current branch is clean, or you are on a dedicated docs-sync branch.
 
@@ -66,7 +66,7 @@ Use upstream order: newest version first.
 Upstream entries look like this:
 
 ```markdown
-- [#317](https://github.com/...) [`2f51db4`](https://github.com/...) - Clean up lint warnings ...
+- [#317](https://github.com/Pythoughts-labs/pythinker-code/pull/317) [`2f51db4`](https://github.com/Pythoughts-labs/pythinker-code/commit/2f51db4) - Clean up lint warnings ...
 ```
 
 Keep:

.changeset/windows-launcher-execve.md

@@ -0,0 +1,5 @@
+---
+'@pythoughts/pythinker-code': patch
+---
+
+Fix the CLI failing to start on Windows with "process.execve is unavailable" by using the spawn fallback instead of calling execve there.

apps/pythinker-code/src/launcher.ts

@@ -116,17 +116,21 @@ async function launch(): Promise<void> {
     ...process.env,
     [FFI_CHILD_ENV]: '1',
   };
+  // On Windows, process.execve either does not exist or exists but throws
+  // ERR_FEATURE_UNAVAILABLE_ON_PLATFORM when called — checking for undefined
+  // is not enough, so always take the spawn fallback there.
+  if (process.platform === 'win32') {
+    launchWindowsFallback(nodeArguments, environment);
+    return;
+  }
+
   // execve keeps the same pid, process group, session, and controlling
   // terminal, so Ctrl+C and job-control signals keep flowing to the app and
   // the child's process group stays the terminal's foreground group.
-  if (process.execve !== undefined) {
-    process.execve(process.execPath, [process.execPath, ...nodeArguments], environment);
-  }
-
-  if (process.platform !== 'win32') {
+  if (process.execve === undefined) {
     throw new Error('process.execve is unavailable on this platform');
   }
-  launchWindowsFallback(nodeArguments, environment);
+  process.execve(process.execPath, [process.execPath, ...nodeArguments], environment);
 }
 
 void launch().catch((error: unknown) => {

apps/pythinker-code/test/cli/ffi-launcher.test.ts

@@ -160,6 +160,37 @@ describe('FFI launcher', () => {
     expect(details.pid === originalPid).toBe(process.platform !== 'win32');
   });
 
+  it('uses the spawn fallback on win32 even when process.execve exists but throws', async () => {
+    // Regression: Windows Node ships process.execve as a defined function that
+    // throws ERR_FEATURE_UNAVAILABLE_ON_PLATFORM when called. The launcher must
+    // route win32 to the spawn fallback without ever calling execve.
+    const patchPath = join(fixtureDir, 'patch-win32.mjs');
+    await writeFile(
+      patchPath,
+      `
+      Object.defineProperty(process, 'platform', { value: 'win32', configurable: true });
+      process.execve = () => {
+        throw new Error('The feature process.execve is unavailable on the current platform');
+      };
+      `,
+    );
+    await writeMain(`
+      process.stdout.write(JSON.stringify({ imported: true, marker: process.env.PYTHINKER_CODE_FFI_CHILD }));
+    `);
+
+    const child = spawn(
+      process.execPath,
+      ['--import', tsxLoader, '--import', patchPath, launcherPath],
+      { cwd: fixtureDir, env: { ...process.env }, stdio: 'pipe' },
+    );
+    const result = await collect(child);
+
+    expect(result.stderr).not.toContain('process.execve is unavailable');
+    expect(result.code).toBe(0);
+    const details = JSON.parse(result.stdout) as { imported: boolean; marker: string };
+    expect(details).toMatchObject({ imported: true, marker: '1' });
+  });
+
   it.skipIf(process.platform === 'win32')(
     'preserves the parent process group and session across execve',
     async () => {