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.
