feat: enhance git diff functionality for untracked files

- Implemented synthetic diff generation for untracked files in both git and non-git directories.
- Added fallback UI in the GitDiffPanel for files without diff content, ensuring better user experience.
- Improved error handling and logging for git operations, enhancing reliability in file diff retrieval.

This update allows users to see diffs for new files that are not yet tracked by git, improving the overall functionality of the diff panel.

apps/server/src/routes/common.ts

@@ -3,9 +3,198 @@
  */
 
 import { createLogger } from "../lib/logger.js";
+import fs from "fs/promises";
+import path from "path";
 
 type Logger = ReturnType<typeof createLogger>;
 
+// Max file size for generating synthetic diffs (1MB)
+const MAX_SYNTHETIC_DIFF_SIZE = 1024 * 1024;
+
+// Binary file extensions to skip
+const BINARY_EXTENSIONS = new Set([
+  ".png", ".jpg", ".jpeg", ".gif", ".bmp", ".ico", ".webp", ".svg",
+  ".pdf", ".doc", ".docx", ".xls", ".xlsx", ".ppt", ".pptx",
+  ".zip", ".tar", ".gz", ".rar", ".7z",
+  ".exe", ".dll", ".so", ".dylib",
+  ".mp3", ".mp4", ".wav", ".avi", ".mov", ".mkv",
+  ".ttf", ".otf", ".woff", ".woff2", ".eot",
+  ".db", ".sqlite", ".sqlite3",
+  ".pyc", ".pyo", ".class", ".o", ".obj",
+]);
+
+/**
+ * Check if a file is likely binary based on extension
+ */
+function isBinaryFile(filePath: string): boolean {
+  const ext = path.extname(filePath).toLowerCase();
+  return BINARY_EXTENSIONS.has(ext);
+}
+
+/**
+ * Generate a synthetic unified diff for an untracked (new) file
+ * This is needed because `git diff HEAD` doesn't include untracked files
+ */
+export async function generateSyntheticDiffForNewFile(
+  basePath: string,
+  relativePath: string
+): Promise<string> {
+  const fullPath = path.join(basePath, relativePath);
+
+  try {
+    // Check if it's a binary file
+    if (isBinaryFile(relativePath)) {
+      return `diff --git a/${relativePath} b/${relativePath}
+new file mode 100644
+index 0000000..0000000
+Binary file ${relativePath} added
+`;
+    }
+
+    // Get file stats to check size
+    const stats = await fs.stat(fullPath);
+    if (stats.size > MAX_SYNTHETIC_DIFF_SIZE) {
+      const sizeKB = Math.round(stats.size / 1024);
+      return `diff --git a/${relativePath} b/${relativePath}
+new file mode 100644
+index 0000000..0000000
+--- /dev/null
++++ b/${relativePath}
+@@ -0,0 +1 @@
++[File too large to display: ${sizeKB}KB]
+`;
+    }
+
+    // Read file content
+    const content = await fs.readFile(fullPath, "utf-8");
+    const lines = content.split("\n");
+
+    // Remove trailing empty line if the file ends with newline
+    if (lines.length > 0 && lines[lines.length - 1] === "") {
+      lines.pop();
+    }
+
+    // Generate diff format
+    const lineCount = lines.length;
+    const addedLines = lines.map(line => `+${line}`).join("\n");
+
+    return `diff --git a/${relativePath} b/${relativePath}
+new file mode 100644
+index 0000000..0000000
+--- /dev/null
++++ b/${relativePath}
+@@ -0,0 +1,${lineCount} @@
+${addedLines}
+`;
+  } catch (error) {
+    // If we can't read the file, return a placeholder diff
+    return `diff --git a/${relativePath} b/${relativePath}
+new file mode 100644
+index 0000000..0000000
+--- /dev/null
++++ b/${relativePath}
+@@ -0,0 +1 @@
++[Unable to read file content]
+`;
+  }
+}
+
+/**
+ * Generate synthetic diffs for all untracked files and combine with existing diff
+ */
+export async function appendUntrackedFileDiffs(
+  basePath: string,
+  existingDiff: string,
+  files: Array<{ status: string; path: string }>
+): Promise<string> {
+  // Find untracked files (status "?")
+  const untrackedFiles = files.filter(f => f.status === "?");
+
+  if (untrackedFiles.length === 0) {
+    return existingDiff;
+  }
+
+  // Generate synthetic diffs for each untracked file
+  const syntheticDiffs = await Promise.all(
+    untrackedFiles.map(f => generateSyntheticDiffForNewFile(basePath, f.path))
+  );
+
+  // Combine existing diff with synthetic diffs
+  const combinedDiff = existingDiff + syntheticDiffs.join("");
+
+  return combinedDiff;
+}
+
+/**
+ * List all files in a directory recursively (for non-git repositories)
+ * Excludes hidden files/folders and common build artifacts
+ */
+export async function listAllFilesInDirectory(
+  basePath: string,
+  relativePath: string = ""
+): Promise<string[]> {
+  const files: string[] = [];
+  const fullPath = path.join(basePath, relativePath);
+
+  // Directories to skip
+  const skipDirs = new Set([
+    "node_modules", ".git", ".automaker", "dist", "build",
+    ".next", ".nuxt", "__pycache__", ".cache", "coverage"
+  ]);
+
+  try {
+    const entries = await fs.readdir(fullPath, { withFileTypes: true });
+
+    for (const entry of entries) {
+      // Skip hidden files/folders (except we want to allow some)
+      if (entry.name.startsWith(".") && entry.name !== ".env") {
+        continue;
+      }
+
+      const entryRelPath = relativePath ? `${relativePath}/${entry.name}` : entry.name;
+
+      if (entry.isDirectory()) {
+        if (!skipDirs.has(entry.name)) {
+          const subFiles = await listAllFilesInDirectory(basePath, entryRelPath);
+          files.push(...subFiles);
+        }
+      } else if (entry.isFile()) {
+        files.push(entryRelPath);
+      }
+    }
+  } catch {
+    // Ignore errors (permission denied, etc.)
+  }
+
+  return files;
+}
+
+/**
+ * Generate diffs for all files in a non-git directory
+ * Treats all files as "new" files
+ */
+export async function generateDiffsForNonGitDirectory(
+  basePath: string
+): Promise<{ diff: string; files: Array<{ status: string; path: string; statusText: string }> }> {
+  const allFiles = await listAllFilesInDirectory(basePath);
+
+  const files = allFiles.map(filePath => ({
+    status: "?",
+    path: filePath,
+    statusText: "New",
+  }));
+
+  // Generate synthetic diffs for all files
+  const syntheticDiffs = await Promise.all(
+    files.map(f => generateSyntheticDiffForNewFile(basePath, f.path))
+  );
+
+  return {
+    diff: syntheticDiffs.join(""),
+    files,
+  };
+}
+
 /**
  * Get error message from error object
  */