feat: add @automaker/git-utils package

ELIMINATES routes/common.ts: Extract all git operations (382 lines) into dedicated package.

- Extract git status parsing (parseGitStatus, isGitRepo)
- Extract diff generation (generateSyntheticDiffForNewFile, etc.)
- Extract repository analysis (getGitRepositoryDiffs)
- Handle both git repos and non-git directories
- Support binary file detection
- Generate synthetic diffs for untracked files

Split into logical modules:
- types.ts: Constants and interfaces
- status.ts: Git status operations
- diff.ts: Diff generation utilities

This package will replace:
- apps/server/src/routes/common.ts (to be deleted)

Dependencies: @automaker/types, @automaker/utils

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

libs/git-utils/src/diff.ts

@@ -0,0 +1,240 @@
+/**
+ * Git diff generation utilities
+ */
+
+import { createLogger } from '@automaker/utils';
+import fs from "fs/promises";
+import path from "path";
+import { exec } from "child_process";
+import { promisify } from "util";
+import { BINARY_EXTENSIONS, type FileStatus } from './types';
+import { isGitRepo, parseGitStatus } from './status';
+
+const execAsync = promisify(exec);
+const logger = createLogger("GitUtils");
+
+// Max file size for generating synthetic diffs (1MB)
+const MAX_SYNTHETIC_DIFF_SIZE = 1024 * 1024;
+
+/**
+ * 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: ${sizeKB}KB]
+`;
+    }
+
+    // Read file content
+    const content = await fs.readFile(fullPath, "utf-8");
+    const hasTrailingNewline = content.endsWith("\n");
+    const lines = content.split("\n");
+
+    // Remove trailing empty line if the file ends with newline
+    if (lines.length > 0 && lines.at(-1) === "") {
+      lines.pop();
+    }
+
+    // Generate diff format
+    const lineCount = lines.length;
+    const addedLines = lines.map(line => `+${line}`).join("\n");
+
+    let diff = `diff --git a/${relativePath} b/${relativePath}
+new file mode 100644
+index 0000000..0000000
+--- /dev/null
++++ b/${relativePath}
+@@ -0,0 +1,${lineCount} @@
+${addedLines}`;
+
+    // Add "No newline at end of file" indicator if needed
+    if (!hasTrailingNewline && content.length > 0) {
+      diff += "\n\\ No newline at end of file";
+    }
+
+    return diff + "\n";
+  } catch (error) {
+    // Log the error for debugging
+    logger.error(`Failed to generate synthetic diff for ${fullPath}:`, error);
+    // Return a placeholder diff
+    return `diff --git a/${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 (error) {
+    // Log the error to help diagnose file system issues
+    logger.error(`Error reading directory ${fullPath}:`, error);
+  }
+
+  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: FileStatus[] }> {
+  const allFiles = await listAllFilesInDirectory(basePath);
+
+  const files: FileStatus[] = 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 git repository diffs for a given path
+ * Handles both git repos and non-git directories
+ */
+export async function getGitRepositoryDiffs(
+  repoPath: string
+): Promise<{ diff: string; files: FileStatus[]; hasChanges: boolean }> {
+  // Check if it's a git repository
+  const isRepo = await isGitRepo(repoPath);
+
+  if (!isRepo) {
+    // Not a git repo - list all files and treat them as new
+    const result = await generateDiffsForNonGitDirectory(repoPath);
+    return {
+      diff: result.diff,
+      files: result.files,
+      hasChanges: result.files.length > 0,
+    };
+  }
+
+  // Get git diff and status
+  const { stdout: diff } = await execAsync("git diff HEAD", {
+    cwd: repoPath,
+    maxBuffer: 10 * 1024 * 1024,
+  });
+  const { stdout: status } = await execAsync("git status --porcelain", {
+    cwd: repoPath,
+  });
+
+  const files = parseGitStatus(status);
+
+  // Generate synthetic diffs for untracked (new) files
+  const combinedDiff = await appendUntrackedFileDiffs(repoPath, diff, files);
+
+  return {
+    diff: combinedDiff,
+    files,
+    hasChanges: files.length > 0,
+  };
+}