diff --git a/.forgejo/workflows/ci.yml b/.forgejo/workflows/ci.yml
index 931d0ea..181a577 100644
--- a/.forgejo/workflows/ci.yml
+++ b/.forgejo/workflows/ci.yml
@@ -6,6 +6,24 @@ on:
   pull_request:
 
 jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install package with dev extras
+        run: pip install -e ".[dev]"
+
+      - name: Ruff (lint)
+        run: ruff check src/ tests/
+
+      - name: Mypy (type check)
+        run: mypy
+
   test:
     runs-on: ubuntu-latest
     strategy:
diff --git a/docs/SECURITY_AND_OPERATIONS.md b/docs/SECURITY_AND_OPERATIONS.md
index 6d1d2b6..62b1230 100644
--- a/docs/SECURITY_AND_OPERATIONS.md
+++ b/docs/SECURITY_AND_OPERATIONS.md
@@ -34,7 +34,8 @@ testbar von der Orchestrierung.
 
 1. **Eingebaute Defaults** (`config.builtin_defaults()`) — spiegeln die
    Standardwerte der ursprünglichen Shell-Skripte wider (Image
-   `ghcr.io/ggml-org/llama.cpp:server-cuda`, `host_port=8001`,
+   `ghcr.io/ggml-org/llama.cpp` per Digest gepinnt für Reproduzierbarkeit,
+   `host_port=8001`,
    `container_name=va_llm`, `gpu_device=1`, `jinja/fa/kv_unified/
    cont_batching/no_context_shift=true`, `reasoning=on`,
    `cache_type_k/v=q4_0`, `batch_size=1024`, `ubatch_size=512`,
diff --git a/llama.cpp.config.example b/llama.cpp.config.example
index f9f5e77..628da02 100644
--- a/llama.cpp.config.example
+++ b/llama.cpp.config.example
@@ -14,7 +14,9 @@
 # locking (--change), and --stop/--check targeting.
 
 [default]
-image = ghcr.io/ggml-org/llama.cpp:server-cuda
+# Pinned by digest for reproducibility. The :server-cuda tag is a moving target;
+# to update, pull it, read the new digest, and replace the pin below.
+image = ghcr.io/ggml-org/llama.cpp@sha256:5535de118ed457f761cbfeacd7e10fef31cb391ca7cac1d5c78b11d28fcf88e6
 # hf_home unterstützt Environment-Variablen und ~, z. B. hf_home = ${HF_HOME}
 hf_home = /srv/models
 model_path = qwen3/default.gguf
diff --git a/pyproject.toml b/pyproject.toml
index 4a3e8d0..55eea2a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -17,6 +17,9 @@ dependencies = [
 [project.optional-dependencies]
 dev = [
     "pytest>=7.4",
+    "ruff>=0.6",
+    "mypy>=1.11",
+    "types-requests",
 ]
 
 [project.scripts]
@@ -27,3 +30,13 @@ where = ["src"]
 
 [tool.setuptools.package-data]
 llamacppctl = ["py.typed"]
+
+[tool.ruff]
+target-version = "py310"
+line-length = 100
+
+[tool.mypy]
+python_version = "3.10"
+files = ["src/llamacppctl"]
+warn_unused_ignores = true
+warn_redundant_casts = true
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 167e7b9..697d674 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -2,3 +2,6 @@
 # in pyproject.toml).
 -r requirements.txt
 pytest>=7.4
+ruff>=0.6
+mypy>=1.11
+types-requests
diff --git a/src/llamacppctl/config.py b/src/llamacppctl/config.py
index 353f910..301ba9a 100644
--- a/src/llamacppctl/config.py
+++ b/src/llamacppctl/config.py
@@ -36,7 +36,10 @@ class ConfigError(ValueError):
 def builtin_defaults() -> dict:
     """Mirrors the original start-llm-server.sh / status-llm-server.sh defaults."""
     return {
-        "image": "ghcr.io/ggml-org/llama.cpp:server-cuda",
+        # Pinned by digest for reproducibility (the :server-cuda tag is a moving
+        # target). To update: docker pull ghcr.io/ggml-org/llama.cpp:server-cuda,
+        # read the new digest, and bump it here (or override `image` in the config).
+        "image": "ghcr.io/ggml-org/llama.cpp@sha256:5535de118ed457f761cbfeacd7e10fef31cb391ca7cac1d5c78b11d28fcf88e6",
         "hf_home": "/models",
         "model_path": "qwen3/default.gguf",
         "container_name": "va_llm",
diff --git a/src/llamacppctl/docker_ops.py b/src/llamacppctl/docker_ops.py
index 08e8f44..40c0669 100644
--- a/src/llamacppctl/docker_ops.py
+++ b/src/llamacppctl/docker_ops.py
@@ -11,7 +11,6 @@ import shlex
 import subprocess
 from dataclasses import dataclass
 from pathlib import Path
-from typing import Optional
 
 from .schema import ServerConfig
 
diff --git a/src/llamacppctl/lock_ops.py b/src/llamacppctl/lock_ops.py
index dd177d4..c3b7d57 100644
--- a/src/llamacppctl/lock_ops.py
+++ b/src/llamacppctl/lock_ops.py
@@ -8,6 +8,7 @@ from __future__ import annotations
 
 import fcntl
 from pathlib import Path
+from typing import TextIO
 
 
 class LockError(RuntimeError):
@@ -17,7 +18,7 @@ class LockError(RuntimeError):
 class FileLock:
     def __init__(self, path: Path):
         self.path = Path(path)
-        self.fd = None
+        self.fd: TextIO | None = None
 
     def __enter__(self) -> "FileLock":
         self.path.parent.mkdir(parents=True, exist_ok=True)
diff --git a/src/llamacppctl/prompt_io.py b/src/llamacppctl/prompt_io.py
index ee04ac5..32a8b67 100644
--- a/src/llamacppctl/prompt_io.py
+++ b/src/llamacppctl/prompt_io.py
@@ -202,7 +202,10 @@ def _pin_dns(host: str, allowed_ips: list):
                 )
         return results
 
-    socket.getaddrinfo = pinned
+    # Intentional monkeypatch: pin DNS to the pre-validated addresses for the
+    # duration of the request (SSRF/rebinding defense). Signature differs from
+    # the stdlib function, hence the targeted ignore.
+    socket.getaddrinfo = pinned  # type: ignore[assignment]
     try:
         yield
     finally: