feat(coding-agent): fetch portable git bash on windows

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- Added automatic Portable Git Bash downloads on Windows when no bash shell is installed.
+
 ### Fixed
 
 - Fixed npm-family package commands on Windows to avoid shell argument splitting when install prefixes contain spaces ([#4623](https://github.com/earendil-works/pi/issues/4623)).

packages/coding-agent/docs/windows.md

@@ -4,9 +4,10 @@ Pi requires a bash shell 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)
+3. Managed Portable Git Bash (`~/.pi/agent/bin/portable-git/bin/bash.exe`)
+4. `bash.exe` on PATH (Cygwin, MSYS2, WSL)
 
-For most users, [Git for Windows](https://git-scm.com/download/win) is sufficient.
+If no bash is found, Pi downloads Git for Windows Portable Git into `~/.pi/agent/bin/portable-git`. Set `PI_OFFLINE=1` to disable automatic downloads.
 
 ## Custom Shell Path
 

packages/coding-agent/src/core/tools/bash.ts

@@ -8,7 +8,7 @@ import { truncateToVisualLines } from "../../modes/interactive/components/visual
 import { theme } from "../../modes/interactive/theme/theme.js";
 import { waitForChildProcess } from "../../utils/child-process.js";
 import {
-	getShellConfig,
+	ensureShellConfig,
 	getShellEnv,
 	killProcessTree,
 	trackDetachedChildPid,
@@ -64,13 +64,13 @@ export interface BashOperations {
  */
 export function createLocalBashOperations(options?: { shellPath?: string }): BashOperations {
 	return {
-		exec: (command, cwd, { onData, signal, timeout, env }) => {
+		exec: async (command, cwd, { onData, signal, timeout, env }) => {
+			if (!existsSync(cwd)) {
+				throw new Error(`Working directory does not exist: ${cwd}\nCannot execute bash commands.`);
+			}
+			const { shell, args } = await ensureShellConfig(options?.shellPath, { silent: true });
+
 			return new Promise((resolve, reject) => {
-				const { shell, args } = getShellConfig(options?.shellPath);
-				if (!existsSync(cwd)) {
-					reject(new Error(`Working directory does not exist: ${cwd}\nCannot execute bash commands.`));
-					return;
-				}
 				const child = spawn(shell, [...args, command], {
 					cwd,
 					detached: process.platform !== "win32",

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -89,7 +89,7 @@ import { extensionForImageMimeType, readClipboardImage } from "../../utils/clipb
 import { parseGitUrl } from "../../utils/git.js";
 import { getCwdRelativePath } from "../../utils/paths.js";
 import { getPiUserAgent } from "../../utils/pi-user-agent.js";
-import { killTrackedDetachedChildren } from "../../utils/shell.js";
+import { ensureWindowsBash, killTrackedDetachedChildren } from "../../utils/shell.js";
 import { ensureTool } from "../../utils/tools-manager.js";
 import { checkForNewPiVersion } from "../../utils/version-check.js";
 import { ArminComponent } from "./components/armin.js";
@@ -567,9 +567,13 @@ export class InteractiveMode {
 		// Load changelog (only show new entries, skip for resumed sessions)
 		this.changelogMarkdown = this.getChangelogForDisplay();
 
-		// Ensure fd and rg are available (downloads if missing, adds to PATH via getBinDir)
-		// Both are needed: fd for autocomplete, rg for grep tool and bash commands
-		const [fdPath] = await Promise.all([ensureTool("fd"), ensureTool("rg")]);
+		// Ensure fd, rg, and Windows bash are available, downloading missing tools under getBinDir.
+		// fd is needed for autocomplete, rg for grep and bash commands, bash for shell execution on Windows.
+		const [fdPath] = await Promise.all([
+			ensureTool("fd"),
+			ensureTool("rg"),
+			ensureWindowsBash(this.settingsManager.getShellPath()),
+		]);
 		this.fdPath = fdPath;
 
 		if (this.session.scopedModels.length > 0 && (this.options.verbose || !this.settingsManager.getQuietStartup())) {

packages/coding-agent/src/utils/shell.ts

@@ -2,12 +2,23 @@ import { existsSync } from "node:fs";
 import { delimiter } from "node:path";
 import { spawn, spawnSync } from "child_process";
 import { getBinDir } from "../config.js";
+import {
+	ensureWindowsPortableGitBash,
+	getManagedWindowsPortableGitBashCandidates,
+	getManagedWindowsPortableGitBashPath,
+} from "./tools-manager.js";
 
 export interface ShellConfig {
 	shell: string;
 	args: string[];
 }
 
+function isSystemBashLookupDisabled(): boolean {
+	const value = process.env.__PI_DISABLE_SYSTEM_BASH_LOOKUP;
+	if (!value) return false;
+	return value === "1" || value.toLowerCase() === "true" || value.toLowerCase() === "yes";
+}
+
 /**
  * Find bash executable on PATH (cross-platform)
  */
@@ -47,7 +58,7 @@ function findBashOnPath(): string | null {
  * Resolve shell configuration based on platform and an optional explicit shell path.
  * Resolution order:
  * 1. User-specified shellPath
- * 2. On Windows: Git Bash in known locations, then bash on PATH
+ * 2. On Windows: Git Bash in known locations, managed Portable Git Bash, then bash on PATH
  * 3. On Unix: /bin/bash, then bash on PATH, then fallback to sh
  */
 export function getShellConfig(customShellPath?: string): ShellConfig {
@@ -60,35 +71,51 @@ export function getShellConfig(customShellPath?: string): ShellConfig {
 	}
 
 	if (process.platform === "win32") {
+		const skipSystemBashLookup = isSystemBashLookupDisabled();
+
 		// 2. Try Git Bash in known locations
 		const paths: string[] = [];
-		const programFiles = process.env.ProgramFiles;
-		if (programFiles) {
-			paths.push(`${programFiles}\\Git\\bin\\bash.exe`);
-		}
-		const programFilesX86 = process.env["ProgramFiles(x86)"];
-		if (programFilesX86) {
-			paths.push(`${programFilesX86}\\Git\\bin\\bash.exe`);
-		}
+		if (!skipSystemBashLookup) {
+			const programFiles = process.env.ProgramFiles;
+			if (programFiles) {
+				paths.push(`${programFiles}\\Git\\bin\\bash.exe`);
+			}
+			const programFilesX86 = process.env["ProgramFiles(x86)"];
+			if (programFilesX86) {
+				paths.push(`${programFilesX86}\\Git\\bin\\bash.exe`);
+			}
 
-		for (const path of paths) {
-			if (existsSync(path)) {
-				return { shell: path, args: ["-c"] };
+			for (const path of paths) {
+				if (existsSync(path)) {
+					return { shell: path, args: ["-c"] };
+				}
 			}
 		}
 
+		const managedPortableGitBash = getManagedWindowsPortableGitBashPath();
+		if (managedPortableGitBash) {
+			return { shell: managedPortableGitBash, args: ["-c"] };
+		}
+
 		// 3. Fallback: search bash.exe on PATH (Cygwin, MSYS2, WSL, etc.)
-		const bashOnPath = findBashOnPath();
-		if (bashOnPath) {
-			return { shell: bashOnPath, args: ["-c"] };
+		if (!skipSystemBashLookup) {
+			const bashOnPath = findBashOnPath();
+			if (bashOnPath) {
+				return { shell: bashOnPath, args: ["-c"] };
+			}
 		}
 
 		throw new Error(
 			`No bash shell found. Options:\n` +
 				`  1. Install Git for Windows: https://git-scm.com/download/win\n` +
-				`  2. Add your bash to PATH (Cygwin, MSYS2, etc.)\n` +
-				"  3. Set shellPath in settings.json\n\n" +
-				`Searched Git Bash in:\n${paths.map((p) => `  ${p}`).join("\n")}`,
+				`  2. Let pi download Portable Git Bash automatically\n` +
+				`  3. Add your bash to PATH (Cygwin, MSYS2, etc.)\n` +
+				"  4. Set shellPath in settings.json\n\n" +
+				(skipSystemBashLookup ? "System bash lookup disabled by __PI_DISABLE_SYSTEM_BASH_LOOKUP.\n" : "") +
+				`Searched Git Bash in:\n${paths.map((p) => `  ${p}`).join("\n")}\n` +
+				`Searched managed Portable Git Bash in:\n${getManagedWindowsPortableGitBashCandidates()
+					.map((p) => `  ${p}`)
+					.join("\n")}`,
 		);
 	}
 
@@ -105,6 +132,38 @@ export function getShellConfig(customShellPath?: string): ShellConfig {
 	return { shell: "sh", args: ["-c"] };
 }
 
+export async function ensureShellConfig(
+	customShellPath?: string,
+	options: { silent?: boolean } = {},
+): Promise<ShellConfig> {
+	try {
+		return getShellConfig(customShellPath);
+	} catch (error) {
+		if (customShellPath || process.platform !== "win32") {
+			throw error;
+		}
+
+		const installedBash = await ensureWindowsPortableGitBash(options.silent ?? false);
+		if (installedBash) {
+			return { shell: installedBash, args: ["-c"] };
+		}
+		throw error;
+	}
+}
+
+export async function ensureWindowsBash(
+	customShellPath?: string,
+	silent: boolean = false,
+): Promise<string | undefined> {
+	if (process.platform !== "win32") return undefined;
+	try {
+		const { shell } = await ensureShellConfig(customShellPath, { silent });
+		return shell;
+	} catch {
+		return undefined;
+	}
+}
+
 export function getShellEnv(): NodeJS.ProcessEnv {
 	const binDir = getBinDir();
 	const pathKey = Object.keys(process.env).find((key) => key.toLowerCase() === "path") ?? "PATH";