fix: address Copilot review — refactor git-bash detection and improve error handling

- Refactor: extract shared find_git_bash() function used by both
  create_command and check_claude_status (eliminates code duplication)
- Validate user-specified CLAUDE_CODE_GIT_BASH_PATH exists before using it,
  falling back to auto-detection if the path is invalid
- Check existing error state before setting stderr errors to avoid
  masking more specific earlier errors
- Make zero-output error message platform-aware (git-bash hint only on Windows)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/desktop/src-tauri/src/claude.rs

@@ -571,39 +571,13 @@ fn create_command(
     // Set effort level (default: low for fast responses)
     cmd.env("CLAUDE_CODE_EFFORT_LEVEL", effort_level.unwrap_or("low"));
 
-    // On Windows, auto-detect git-bash if CLAUDE_CODE_GIT_BASH_PATH is not set.
+    // On Windows, ensure CLAUDE_CODE_GIT_BASH_PATH is set.
     // Claude Code requires git-bash to run on Windows.
+    // Uses find_git_bash() which also validates user-specified paths.
     #[cfg(target_os = "windows")]
     {
-        if std::env::var("CLAUDE_CODE_GIT_BASH_PATH").is_err() {
-            // Reuse the same detection logic as is_git_bash_available()
-            let mut found: Option<String> = None;
-            let candidates = [
-                r"C:\Program Files\Git\bin\bash.exe",
-                r"C:\Program Files (x86)\Git\bin\bash.exe",
-            ];
-            for candidate in &candidates {
-                if std::path::Path::new(candidate).is_file() {
-                    found = Some(candidate.to_string());
-                    break;
-                }
-            }
-            // Also try deriving from git.exe on PATH
-            if found.is_none() {
-                if let Ok(git_path) = which::which("git") {
-                    if let Some(cmd_dir) = git_path.parent() {
-                        if let Some(git_root) = cmd_dir.parent() {
-                            let bash = git_root.join("bin").join("bash.exe");
-                            if bash.is_file() {
-                                found = Some(bash.to_string_lossy().to_string());
-                            }
-                        }
-                    }
-                }
-            }
-            if let Some(bash_path) = found {
-                cmd.env("CLAUDE_CODE_GIT_BASH_PATH", bash_path);
-            }
+        if let Some(bash_path) = find_git_bash() {
+            cmd.env("CLAUDE_CODE_GIT_BASH_PATH", bash_path);
         }
     }
 
@@ -904,13 +878,15 @@ pub struct ClaudeStatus {
     pub missing_git: bool,
 }
 
-/// Check whether Git for Windows (git-bash) is available on Windows.
+/// Find the path to git-bash on Windows.
+/// Returns `Some(path)` if found, `None` otherwise.
+/// Used by both `create_command` (to set the env var) and `check_claude_status` (to report status).
 #[cfg(target_os = "windows")]
-fn is_git_bash_available() -> bool {
-    // 1. User-specified override
+fn find_git_bash() -> Option<String> {
+    // 1. User-specified override (only if the path actually exists)
     if let Ok(p) = std::env::var("CLAUDE_CODE_GIT_BASH_PATH") {
-        if PathBuf::from(&p).exists() {
-            return true;
+        if PathBuf::from(&p).is_file() {
+            return Some(p);
         }
     }
 
@@ -920,8 +896,8 @@ fn is_git_bash_available() -> bool {
         r"C:\Program Files (x86)\Git\bin\bash.exe",
     ];
     for path in &candidates {
-        if PathBuf::from(path).exists() {
-            return true;
+        if PathBuf::from(path).is_file() {
+            return Some(path.to_string());
         }
     }
 
@@ -930,22 +906,27 @@ fn is_git_bash_available() -> bool {
         // git.exe is typically at Git/cmd/git.exe → bash.exe at Git/bin/bash.exe
         if let Some(cmd_dir) = git_path.parent() {
             if let Some(git_root) = cmd_dir.parent() {
-                if git_root.join("bin").join("bash.exe").exists() {
-                    return true;
+                let bash = git_root.join("bin").join("bash.exe");
+                if bash.is_file() {
+                    return Some(bash.to_string_lossy().to_string());
                 }
             }
         }
     }
 
     // 4. bash directly on PATH
-    which::which("bash").is_ok()
+    if let Ok(bash_path) = which::which("bash") {
+        return Some(bash_path.to_string_lossy().to_string());
+    }
+
+    None
 }
 
 #[tauri::command]
 pub async fn check_claude_status() -> Result<ClaudeStatus, String> {
     // On Windows, check for Git for Windows first — Claude Code requires it.
     #[cfg(target_os = "windows")]
-    let missing_git = !is_git_bash_available();
+    let missing_git = find_git_bash().is_none();
     #[cfg(not(target_os = "windows"))]
     let missing_git = false;
 

apps/desktop/src/hooks/use-claude-events.ts

@@ -308,9 +308,12 @@ export function useClaudeEvents() {
         !chatStore._cancelledByUser
       ) {
         if (count === 0) {
+          const isWindows = navigator.userAgent.includes("Windows");
           chatStore._setError(
             tabId,
-            "Claude process failed to start. Check that Claude Code CLI is installed and git-bash is available on Windows.",
+            isWindows
+              ? "Claude process failed to start. Check that Claude Code CLI is installed and git-bash is available."
+              : "Claude process failed to start. Check that Claude Code CLI is installed.",
           );
         } else {
           chatStore._setError(
@@ -423,11 +426,13 @@ export function useClaudeEvents() {
             ) {
               log.error(`[${tabId}] CRITICAL: ${payload}`);
             }
-            // Surface critical stderr messages to the user UI
+            // Surface critical stderr messages to the user UI (only if no error is already set)
             if (
-              payload.includes("git-bash") ||
-              payload.includes("git bash") ||
-              payload.includes("bash.exe")
+              (payload.includes("git-bash") ||
+                payload.includes("git bash") ||
+                payload.includes("bash.exe")) &&
+              !useClaudeChatStore.getState().tabs.find((t) => t.id === tabId)
+                ?.error
             ) {
               useClaudeChatStore
                 .getState()