feat(coder): add import-drop detection to edit safety guards

- checkDroppedImports detects removed import/require lines in edits
- Runs alongside truncation guard in pending_changes.ts
- Supports ESM imports, CJS require, type imports, side-effect imports

apps/coder/src/services/edit-guards-imports.ts

@@ -0,0 +1,47 @@
+// edit-guards-imports — detects dropped imports in edited files.
+// Ported from opencode-morph-fast-apply (MIT).
+
+export interface ImportCheckResult {
+  ok: boolean;
+  missingImports: string[];
+  reason?: string;
+}
+
+const IMPORT_PATTERNS = [
+  /^import\s+(?:\{[^}]*\}|\*\s+as\s+\w+|\w+)\s+from\s+['"][^'"]+['"]\s*;?$/m,
+  /^import\s+['"][^'"]+['"]\s*;?$/m,
+  /^export\s+.*\s+from\s+['"][^'"]+['"]\s*;?$/m,
+  /^require\s*\(\s*['"][^'"]+['"]\s*\)\s*;?$/m,
+  /^import\s+type\s+\{[^}]*\}\s+from\s+['"][^'"]+['"]\s*;?$/m,
+];
+
+function extractImportLines(content: string): string[] {
+  return content.split('\n').filter((line) =>
+    IMPORT_PATTERNS.some((p) => p.test(line.trim())),
+  );
+}
+
+export function checkDroppedImports(
+  original: string,
+  updated: string,
+  filePath: string,
+): ImportCheckResult {
+  const originalImports = extractImportLines(original);
+  const updatedImports = extractImportLines(updated);
+
+  if (originalImports.length === 0) {
+    return { ok: true, missingImports: [] };
+  }
+
+  const missing = originalImports.filter((imp) => !updatedImports.includes(imp));
+
+  if (missing.length > 0 && originalImports.length > 0) {
+    return {
+      ok: false,
+      missingImports: missing,
+      reason: `Edit would drop ${missing.length} import(s) from ${filePath}`,
+    };
+  }
+
+  return { ok: true, missingImports: [] };
+}