chore(vendor): import pi 0.85.1

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: d981de1229ef899957bbe968bc8dcda02a21f477

third_party/pi/packages/coding-agent/docs/windows.md

@@ -0,0 +1,39 @@
+# Windows Setup
+
+Pi uses Git Bash by default on Windows. Checked locations (in order):
+
+1. Custom path from `~/.pi/agent/settings.json`
+2. Git Bash (`C:\Program Files\Git\bin\bash.exe`)
+3. `bash.exe` on PATH (Cygwin, MSYS2, WSL)
+
+For most users, [Git for Windows](https://git-scm.com/download/win) is sufficient.
+
+## PowerShell Tool
+
+The optional `powershell` tool runs commands through `pwsh.exe` when available, otherwise Windows PowerShell. It starts PowerShell with `-NoProfile -NonInteractive -ExecutionPolicy Bypass`. Administrator-enforced execution policies can still take precedence.
+
+Use `defaultTools` to replace the model-facing `bash` tool:
+
+```json
+{
+  "defaultTools": ["read", "powershell", "edit", "write"]
+}
+```
+
+Or enable both while comparing behavior:
+
+```json
+{
+  "defaultTools": ["read", "bash", "powershell", "edit", "write"]
+}
+```
+
+The `!` and `!!` editor commands still use Bash.
+
+## Custom Bash Path
+
+```json
+{
+  "shellPath": "C:\\cygwin64\\bin\\bash.exe"
+}
+```