Fixes#11592.
## Problem
WSL starts Windows programs in the current directory, translated to
`\\wsl.localhost\<distro>\<cwd>`. When that path exceeds MAX_PATH, every
Windows program fails to start with `Invalid argument`. pi inherits its
cwd when spawning `powershell.exe`, so in a deep directory:
- clipboard image paste returns `null` (the PowerShell backend fails,
stderr is discarded)
- copy via `powershell.exe` (WSL without WSLg) fails
- opening the browser for sign-in fails (`xdg-open` on WSL runs
`explorer.exe`)
Reproduced on WSL (FedoraLinux-44): `powershell.exe` and `cmd.exe` work
from a 225-char cwd and fail from 230. With an image on the Windows
clipboard, `readClipboardImage()` returns the PNG from `/tmp` and `null`
from a 245-char cwd; with this change it returns the PNG from both.
`LongPathsEnabled=1` does not help.
## Changes
- `runClipboardCommand` and `openBrowser` run from `/` on POSIX. These
tools never use the cwd (temp files are passed by absolute path), and
`/` is always the shortest UNC path. `tmpdir()` was not used because
`$TMPDIR` can itself be deep.
- The external editor keeps pi's cwd on purpose, so project-relative
paths and integrated terminals keep working. A Windows editor such as
`code` can still fail from a deep WSL directory, as with git's
`core.editor`. A comment documents this.
- External editor failures were silent: the UI redrew over the error
immediately. pi now shows `Failed to launch external editor: <cmd>`,
`External editor exited with code N; prompt unchanged`, or the signal
name. This shows in the status line for the main editor and inline in
the extension editor dialog.
## Testing
- New tests: clipboard commands run from `/` (POSIX); an editor that
cannot be launched is reported (POSIX); the existing failure test checks
the message.
- Verified on WSL by running the real modules: clipboard image paste
from a deep cwd, and editor success, exit code 1, launch failure, and
SIGTERM.
- On Windows, the 3 existing `external-editor.test.ts` tests already
fail on `main`: the editor command is split on spaces, so `C:\Program
Files\nodejs\node.exe` breaks. Not addressed here.
This PR is AI-generated.
Replace the external clipboard dependency with small macOS, Windows,
and X11 helpers and integrate them into coding-agent.
Run native clipboard operations on worker threads and make command
fallbacks asynchronous. Preserve incremental X11 transfers, legacy text
encodings, native image formats, and existing Wayland and platform tools.
Include native prebuilds with ARM64 page alignment, packaging updates,
and regression coverage.
