Require bash on Windows. Throw error if missing

WINDOWS.md

@@ -79,34 +79,60 @@ Codebuff checks GitHub for the latest release on first run. This fails when:
 
 ---
 
+### Issue: "Bash is required but was not found" Error
+
+**Symptom**:
+```
+Bash is required but was not found on this Windows system.
+```
+
+**Cause**:
+Codebuff requires bash for command execution. This error appears when:
+- Git for Windows is not installed
+- You're not running inside WSL
+- bash.exe is not in your PATH
+
+**Solutions**:
+
+1. **Install Git for Windows** (recommended):
+   - Download from https://git-scm.com/download/win
+   - This installs `bash.exe` which Codebuff will automatically detect
+   - Works in PowerShell, CMD, or Git Bash terminals
+
+2. **Use WSL (Windows Subsystem for Linux)**:
+   - Provides full Linux environment with native bash
+   - Install: `wsl --install` in PowerShell (Admin)
+   - Run codebuff inside WSL for best compatibility
+
+3. **Set custom bash path** (advanced):
+   - If bash.exe is installed in a non-standard location:
+   ```powershell
+   set CODEBUFF_GIT_BASH_PATH=C:\path\to\bash.exe
+   ```
+
+**Reference**: Issue [#274](https://github.com/CodebuffAI/codebuff/issues/274)
+
+---
+
 ### Issue: Git Commands Fail on Windows
 
 **Symptom**:
 Git operations (commit, rebase, complex commands) fail with syntax errors or unexpected behavior.
 
 **Cause**:
-Codebuff uses Windows `cmd.exe` for command execution, which:
-- Does not support bash syntax (HEREDOC, process substitution)
-- Has limited quote escaping compared to bash
-- Cannot execute complex git commands that work in Git Bash
+Complex git commands may have issues with Windows path handling or shell escaping.
 
 **Solutions**:
 
-1. **Install Git for Windows** (if not already installed):
+1. **Ensure Git for Windows is installed**:
    - Download from https://git-scm.com/download/win
-   - Ensures git commands are available in PATH
-
-2. **Use Git Bash terminal** instead of PowerShell:
-   - Git Bash provides better compatibility with bash-style commands
-   - Launch Git Bash and run `codebuff` from there
+   - Codebuff uses bash.exe from Git for Windows for command execution
 
-3. **Or use WSL (Windows Subsystem for Linux)**:
+2. **Use WSL for complex operations**:
    - Provides full Linux environment with native bash
    - Install: `wsl --install` in PowerShell (Admin)
    - Run codebuff inside WSL for best compatibility
 
-**Note**: Even when running in Git Bash, Codebuff spawns commands using `cmd.exe`. Using WSL provides the most reliable experience for git operations.
-
 **Reference**: Issue [#274](https://github.com/CodebuffAI/codebuff/issues/274)
 
 ---

sdk/src/run-state.ts

@@ -502,7 +502,7 @@ export async function initialSessionState(
     shellConfigFiles: {},
     systemInfo: {
       platform: process.platform,
-      shell: process.platform === 'win32' ? 'cmd.exe' : 'bash',
+      shell: 'bash',
       nodeVersion: process.version,
       arch: process.arch,
       homedir: os.homedir(),

sdk/src/tools/run-terminal-command.ts

@@ -1,4 +1,5 @@
 import { spawn } from 'child_process'
+import * as fs from 'fs'
 import * as os from 'os'
 import * as path from 'path'
 
@@ -12,6 +13,75 @@ import type { CodebuffToolOutput } from '../../../common/src/tools/list'
 
 const COMMAND_OUTPUT_LIMIT = 50_000
 
+// Common locations where Git Bash might be installed on Windows
+const GIT_BASH_COMMON_PATHS = [
+  'C:\\Program Files\\Git\\bin\\bash.exe',
+  'C:\\Program Files (x86)\\Git\\bin\\bash.exe',
+  'C:\\Git\\bin\\bash.exe',
+]
+
+/**
+ * Find bash executable on Windows.
+ * Priority:
+ * 1. CODEBUFF_GIT_BASH_PATH environment variable
+ * 2. bash.exe in PATH (e.g., inside WSL or Git Bash terminal)
+ * 3. Common Git Bash installation locations
+ */
+function findWindowsBash(env: NodeJS.ProcessEnv): string | null {
+  // Check for user-specified path via environment variable
+  const customPath = env.CODEBUFF_GIT_BASH_PATH
+  if (customPath && fs.existsSync(customPath)) {
+    return customPath
+  }
+
+  // Check if bash.exe is in PATH (works inside WSL or Git Bash)
+  const pathEnv = env.PATH || env.Path || ''
+  const pathDirs = pathEnv.split(path.delimiter)
+
+  for (const dir of pathDirs) {
+    const bashPath = path.join(dir, 'bash.exe')
+    if (fs.existsSync(bashPath)) {
+      return bashPath
+    }
+    // Also check for just 'bash' (for WSL)
+    const bashPathNoExt = path.join(dir, 'bash')
+    if (fs.existsSync(bashPathNoExt)) {
+      return bashPathNoExt
+    }
+  }
+
+  // Check common Git Bash installation locations
+  for (const commonPath of GIT_BASH_COMMON_PATHS) {
+    if (fs.existsSync(commonPath)) {
+      return commonPath
+    }
+  }
+
+  return null
+}
+
+/**
+ * Create an error message for Windows users when bash is not available.
+ */
+function createWindowsBashNotFoundError(): Error {
+  return new Error(
+    `Bash is required but was not found on this Windows system.
+
+To fix this, you have several options:
+
+1. Install Git for Windows (includes bash.exe):
+   Download from: https://git-scm.com/download/win
+
+2. Use WSL (Windows Subsystem for Linux):
+   Run in PowerShell (Admin): wsl --install
+   Then run Codebuff inside WSL.
+
+3. Set a custom bash path:
+   Set the CODEBUFF_GIT_BASH_PATH environment variable to your bash.exe location.
+   Example: set CODEBUFF_GIT_BASH_PATH=C:\\path\\to\\bash.exe`,
+  )
+}
+
 export function runTerminalCommand({
   command,
   process_type,
@@ -31,18 +101,33 @@ export function runTerminalCommand({
 
   return new Promise((resolve, reject) => {
     const isWindows = os.platform() === 'win32'
-    const shell = isWindows ? 'cmd.exe' : 'bash'
-    const shellArgs = isWindows ? ['/c'] : ['-c']
+    const processEnv = {
+      ...getSystemProcessEnv(),
+      ...(env ?? {}),
+    } as NodeJS.ProcessEnv
+
+    let shell: string
+    let shellArgs: string[]
+
+    if (isWindows) {
+      const bashPath = findWindowsBash(processEnv)
+      if (!bashPath) {
+        reject(createWindowsBashNotFoundError())
+        return
+      }
+      shell = bashPath
+      shellArgs = ['-c']
+    } else {
+      shell = 'bash'
+      shellArgs = ['-c']
+    }
 
     // Resolve cwd to absolute path
     const resolvedCwd = path.resolve(cwd)
 
     const childProcess = spawn(shell, [...shellArgs, command], {
       cwd: resolvedCwd,
-      env: {
-        ...getSystemProcessEnv(),
-        ...(env ?? {}),
-      } as NodeJS.ProcessEnv,
+      env: processEnv,
       stdio: 'pipe',
     })