OpenAgentHQ · himanshu231204 · Sep 1, 2026 · Aug 31, 2026 · Sep 1, 2026
diff --git a/src/modeldock/adapters/runtimes/gpt4all.py b/src/modeldock/adapters/runtimes/gpt4all.py
@@ -1,7 +1,12 @@
-"""GPT4All runtime adapter (planned). Implements RuntimePort; not yet shipped."""
+"""GPT4All local model-directory discovery.
+
+The adapter deliberately stops at discovery for issue #30. It does not download
+or load models until the remaining GPT4All runtime work is implemented.
+"""
 
 from __future__ import annotations
 
+from pathlib import Path
 from typing import Any, List
 
 from modeldock.adapters.runtimes.base import BaseRuntime
@@ -11,15 +16,25 @@
 
 
 class Gpt4AllRuntime(BaseRuntime):
-    """Planned runtime adapter for GPT4All."""
+    """Discover models already present in a GPT4All models directory."""
 
     backend: RuntimeBackend = RuntimeBackend.GPT4ALL
 
+    def __init__(self, models_dir: Path | None = None) -> None:
+        super().__init__()
+        self._models_dir = models_dir or Path.home() / ".cache" / "gpt4all"
+
     def _check_available(self) -> bool:
-        return False
+        return self._models_dir.is_dir()
 
     def list_installed(self) -> List[ModelRef]:
-        raise RuntimeUnavailableError("gpt4all", hint="Adapter planned, not shipped.")
+        if not self._models_dir.is_dir():
+            return []
+        refs: List[ModelRef] = []
+        for path in sorted(self._models_dir.iterdir(), key=lambda path: path.name):
+            if path.is_file() and path.suffix.lower() in {".gguf", ".bin"}:
+                refs.append(ModelRef.parse(path.stem))
+        return refs
 
     def _do_pull(self, ref: ModelRef, progress: Any) -> PullResult:
         raise RuntimeUnavailableError("gpt4all", hint="Adapter planned, not shipped.")

diff --git a/src/modeldock/adapters/runtimes/registry.py b/src/modeldock/adapters/runtimes/registry.py
@@ -6,6 +6,7 @@
 
 from __future__ import annotations
 
+from pathlib import Path
 from typing import Any, Callable, Dict, List, cast
 
 from modeldock.common.logging import get_logger
@@ -66,6 +67,7 @@ def get(
         backend: RuntimeBackend,
         host: str | None = None,
         gpu_layers: int | None = None,
+        models_dir: Path | None = None,
     ) -> RuntimePort:
         """Return a runtime instance for backend (entry points win).
 
@@ -88,6 +90,8 @@ def get(
                 clear()
         if gpu_layers is not None and hasattr(runtime, "_gpu_layers"):
             runtime._gpu_layers = gpu_layers
+        if models_dir is not None and hasattr(runtime, "_models_dir"):
+            runtime._models_dir = models_dir
         return runtime
 
     @staticmethod

diff --git a/src/modeldock/common/config.py b/src/modeldock/common/config.py
@@ -46,6 +46,7 @@ class Settings(BaseModel):
     ollama_host: Optional[str] = None
     lmstudio_host: Optional[str] = None
     llamacpp_gpu_layers: Optional[int] = None
+    gpt4all_models_dir: Optional[Path] = None
     config_path: Optional[Path] = None
 
     @field_validator("log_level")
@@ -103,6 +104,9 @@ def to_env_overrides(self) -> Dict[str, str]:
             f"{_ENV_PREFIX}CATALOG_SOURCE": self.catalog_source,
             f"{_ENV_PREFIX}AUTO_INSTALL": str(self.auto_install).lower(),
             f"{_ENV_PREFIX}CACHE_DIR": str(self.cache_dir),
+            f"{_ENV_PREFIX}GPT4ALL_MODELS_DIR": ""
+            if self.gpt4all_models_dir is None
+            else str(self.gpt4all_models_dir),
         }
 
 
@@ -181,6 +185,10 @@ def _apply_mapping(settings: Settings, data: Dict[str, Any], source: str = "conf
     if "llamacpp_gpu_layers" in data:
         raw = data["llamacpp_gpu_layers"]
         _safe_set(settings, "llamacpp_gpu_layers", raw if raw not in (None, "") else None, source)
+    if "gpt4all_models_dir" in data:
+        raw = data["gpt4all_models_dir"]
+        resolved_path = Path(str(raw)) if raw not in (None, "") else None
+        _safe_set(settings, "gpt4all_models_dir", resolved_path, source)
 
 
 def load_settings(
@@ -228,6 +236,7 @@ def load_settings(
         f"{_ENV_PREFIX}OLLAMA_HOST": "ollama_host",
         f"{_ENV_PREFIX}LMSTUDIO_HOST": "lmstudio_host",
         f"{_ENV_PREFIX}LLAMACPP_GPU_LAYERS": "llamacpp_gpu_layers",
+        f"{_ENV_PREFIX}GPT4ALL_MODELS_DIR": "gpt4all_models_dir",
     }
     env_data = {
         field_name: os.environ[env_key]

diff --git a/src/modeldock/core/manager.py b/src/modeldock/core/manager.py
@@ -164,6 +164,11 @@ def _resolve_backend_catalog(self, cfg: Settings) -> Optional[RegistryPort]:
         RuntimeBackend.LLAMACPP: "llamacpp_gpu_layers",
     }
 
+    #: Config field holding the local model directory for file-based runtimes.
+    _MODELS_DIR_SETTING_FOR = {
+        RuntimeBackend.GPT4ALL: "gpt4all_models_dir",
+    }
+
     def _resolve_runtime(self, backend: RuntimeBackend, cfg: Settings) -> RuntimePort:
         # Apply the configured host at construction time so it always takes
         # effect (clients are built lazily and cached per instance). Backends
@@ -173,8 +178,15 @@ def _resolve_runtime(self, backend: RuntimeBackend, cfg: Settings) -> RuntimePor
         host = getattr(cfg, host_field, None) if host_field else None
         gpu_layers_field = self._GPU_LAYERS_SETTING_FOR.get(backend)
         gpu_layers = getattr(cfg, gpu_layers_field, None) if gpu_layers_field else None
+        models_dir_field = self._MODELS_DIR_SETTING_FOR.get(backend)
+        models_dir = getattr(cfg, models_dir_field, None) if models_dir_field else None
         try:
-            runtime = self._runtime_registry.get(backend, host=host, gpu_layers=gpu_layers)
+            runtime = self._runtime_registry.get(
+                backend,
+                host=host,
+                gpu_layers=gpu_layers,
+                models_dir=models_dir,
+            )
         except KeyError as exc:
             raise RuntimeUnavailableError(backend.value) from exc
         if not runtime.is_available():

diff --git a/tests/unit/test_config.py b/tests/unit/test_config.py
@@ -33,6 +33,10 @@ def test_settings_llamacpp_gpu_layers_defaults_to_none() -> None:
     assert Settings().llamacpp_gpu_layers is None
 
 
+def test_settings_gpt4all_models_dir_defaults_to_none() -> None:
+    assert Settings().gpt4all_models_dir is None
+
+
 def test_settings_llamacpp_gpu_layers_accepts_non_negative_int() -> None:
     assert Settings(llamacpp_gpu_layers=35).llamacpp_gpu_layers == 35
 
@@ -89,6 +93,14 @@ def test_load_settings_llamacpp_gpu_layers_invalid_env_falls_back(
     assert s.llamacpp_gpu_layers is None
 
 
+def test_load_settings_gpt4all_models_dir_env(
+    monkeypatch: pytest.MonkeyPatch, tmp_path: Path
+) -> None:
+    models_dir = tmp_path / "gpt4all"
+    monkeypatch.setenv("MODELDOCK_GPT4ALL_MODELS_DIR", str(models_dir))
+    assert load_settings().gpt4all_models_dir == models_dir
+
+
 def test_default_cache_dir_override(monkeypatch: pytest.MonkeyPatch, tmp_path: Path) -> None:
     monkeypatch.setenv("MODELDOCK_CACHE_DIR", str(tmp_path))
     assert default_cache_dir() == tmp_path

diff --git a/tests/unit/test_gpt4all_runtime.py b/tests/unit/test_gpt4all_runtime.py
@@ -0,0 +1,39 @@
+"""Unit tests for GPT4All local model discovery (issue #30)."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from modeldock.adapters.runtimes.gpt4all import Gpt4AllRuntime
+from modeldock.adapters.runtimes.registry import RuntimeRegistry
+from modeldock.domain.model import RuntimeBackend
+
+
+def test_list_installed_registers_supported_model_files(tmp_path: Path) -> None:
+    (tmp_path / "Phi-3-mini.Q4_0.gguf").touch()
+    (tmp_path / "legacy-model.bin").touch()
+    (tmp_path / "notes.txt").touch()
+    (tmp_path / "nested").mkdir()
+    (tmp_path / "nested" / "ignored.gguf").touch()
+
+    runtime = Gpt4AllRuntime(models_dir=tmp_path)
+
+    assert runtime.is_available() is True
+    assert [ref.name for ref in runtime.list_installed()] == [
+        "Phi-3-mini.Q4_0",
+        "legacy-model",
+    ]
+
+
+def test_missing_models_directory_is_unavailable_and_empty(tmp_path: Path) -> None:
+    runtime = Gpt4AllRuntime(models_dir=tmp_path / "missing")
+
+    assert runtime.is_available() is False
+    assert runtime.list_installed() == []
+
+
+def test_registry_forwards_gpt4all_models_dir(tmp_path: Path) -> None:
+    runtime = RuntimeRegistry().get(RuntimeBackend.GPT4ALL, models_dir=tmp_path)
+
+    assert isinstance(runtime, Gpt4AllRuntime)
+    assert runtime._models_dir == tmp_path