diff --git a/api/services/extension_process.py b/api/services/extension_process.py
index 89622a2..1ebb2d5 100644
--- a/api/services/extension_process.py
+++ b/api/services/extension_process.py
@@ -12,6 +12,7 @@
 import os
 import platform
 import queue
+import re
 import subprocess
 import sys
 import threading
@@ -20,6 +21,10 @@
 from typing import Callable, Optional
 
 _RUNNER_PATH = Path(__file__).parent.parent / "runner.py"
+_MISSING_MODULE_RE = re.compile(r"No module named ['\"]([^'\"]+)['\"]")
+_AUTO_REPAIR_PACKAGE_MAP = {
+    "PIL": "Pillow",
+}
 
 
 def _venv_python(ext_dir: Path) -> Path:
@@ -91,35 +96,83 @@ def _start(self) -> None:
                 "Run the extension's setup.py first."
             )
 
-        self._proc = subprocess.Popen(
-            [str(python), str(_RUNNER_PATH)],
-            stdin=subprocess.PIPE,
-            stdout=subprocess.PIPE,
-            stderr=subprocess.PIPE,
-            text=True,
-            bufsize=1,
-            env=self._build_env(),
-        )
+        for attempt in range(3):
+            self._queue = queue.Queue()
+            self._proc = subprocess.Popen(
+                [str(python), str(_RUNNER_PATH)],
+                stdin=subprocess.PIPE,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE,
+                text=True,
+                bufsize=1,
+                env=self._build_env(),
+            )
+
+            # Background thread: read stdout → queue
+            reader = threading.Thread(target=self._read_loop, daemon=True)
+            reader.start()
 
-        # Background thread: read stdout → queue
-        reader = threading.Thread(target=self._read_loop, daemon=True)
-        reader.start()
+            # Background thread: forward stderr to our stderr
+            stderr_fwd = threading.Thread(target=self._stderr_loop, daemon=True)
+            stderr_fwd.start()
 
-        # Background thread: forward stderr to our stderr
-        stderr_fwd = threading.Thread(target=self._stderr_loop, daemon=True)
-        stderr_fwd.start()
+            # Wait for ready — runner sends params_schema in this message
+            msg = self._recv(timeout=None)
+            if msg.get("type") == "ready":
+                # Override params_schema with what the generator class actually declares
+                if msg.get("params_schema"):
+                    self._params_schema = msg["params_schema"]
+
+                print(f"[ExtensionProcess] {self.MODEL_ID} subprocess started (pid {self._proc.pid})")
+                return
 
-        # Wait for ready — runner sends params_schema in this message
-        msg = self._recv(timeout=None)
-        if msg.get("type") != "ready":
             self._proc.kill()
-            raise RuntimeError(f"[{self.MODEL_ID}] Expected 'ready', got: {msg}")
+            missing_module = self._extract_missing_module(msg)
+            package_name = self._resolve_auto_repair_package(missing_module) if missing_module else None
+            if package_name and attempt < 2:
+                self._install_missing_package(python, missing_module, package_name)
+                continue
 
-        # Override params_schema with what the generator class actually declares
-        if msg.get("params_schema"):
-            self._params_schema = msg["params_schema"]
+            raise RuntimeError(f"[{self.MODEL_ID}] Expected 'ready', got: {msg}")
 
-        print(f"[ExtensionProcess] {self.MODEL_ID} subprocess started (pid {self._proc.pid})")
+    def _extract_missing_module(self, msg: dict) -> Optional[str]:
+        """Returns missing import name from a runner error payload, if present."""
+        blob = f"{msg.get('message', '')}\n{msg.get('traceback', '')}"
+        match = _MISSING_MODULE_RE.search(blob)
+        return match.group(1) if match else None
+
+    def _resolve_auto_repair_package(self, module_name: str) -> Optional[str]:
+        """
+        Maps a missing import name to a pip package for safe auto-repair.
+
+        Important: do not guess package names for arbitrary missing modules,
+        because that can install wrong packages and break environments.
+        """
+        if module_name in _AUTO_REPAIR_PACKAGE_MAP:
+            return _AUTO_REPAIR_PACKAGE_MAP[module_name]
+        root = module_name.split(".")[0]
+        return _AUTO_REPAIR_PACKAGE_MAP.get(root)
+
+    def _install_missing_package(self, python: Path, module_name: str, package_name: str) -> None:
+        """Best-effort auto-repair for a known missing import in extension venv."""
+        print(
+            f"[ExtensionProcess] {self.MODEL_ID} missing module '{module_name}' "
+            f"-> installing '{package_name}'"
+        )
+        try:
+            subprocess.run(
+                [str(python), "-m", "pip", "install", package_name],
+                check=True,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE,
+                text=True,
+            )
+        except subprocess.CalledProcessError as exc:
+            details = (exc.stderr or exc.stdout or "").strip()
+            raise RuntimeError(
+                f"[{self.MODEL_ID}] Auto-repair failed while installing '{package_name}' "
+                f"for missing module '{module_name}'.\n{details[-2000:]}"
+            ) from exc
 
     def _read_loop(self) -> None:
         """Continuously reads stdout and pushes parsed JSON to the queue."""