feat(37): add MODEL_DIR env override -- enable isolated instances per project (51-ACA)

- config.py: model_dir_override field with validation_alias=MODEL_DIR + populate_by_name=True
- admin.py: _MODEL_DIR constant -> _get_model_dir() function (3 call sites)
- server.py: import and path references updated to _get_model_dir(); utf-8-sig for BOM resilience
- .env.example: MODEL_DIR documentation added
- STATUS.md: session 17c header

Author: Presta

.env.example

@@ -5,6 +5,12 @@ COSMOS_KEY=
 MODEL_DB_NAME=evamodel
 MODEL_CONTAINER_NAME=model_objects
 
+# ── Model Data Directory ──────────────────────────────────────────────────────
+# Leave blank to use the default model/ folder beside this server's code.
+# Set to an absolute path to run an isolated instance for a different project
+# (e.g. MODEL_DIR=C:\myproject\data-model\model). Used by 51-ACA side project.
+MODEL_DIR=
+
 # ── Redis ─────────────────────────────────────────────────────────────────────
 # Leave blank to use in-process memory cache
 REDIS_URL=

STATUS.md

@@ -1,8 +1,8 @@
 # EVA Data Model -- Status
 
-**Last Updated:** February 26, 2026 -- Session 17b: evidence receipts for 25 API stories -- MTI 86 -> 100 -- all 10 readiness gates PASS
+**Last Updated:** February 26, 2026 -- Session 17c: MODEL_DIR override + 51-ACA isolated instance -- services=4 endpoints=14 containers=5 agents=4 total=27
 **Phase:** ACTIVE -- COSMOS 24x7 -- validate-model PASS 0 violations -- 31 layers registered -- MTI=100
-**Snapshot (2026-02-26 S17b):** 31 layers -- 4057 exported objects -- Tests: 41/42 (T36 pre-existing only) -- Readiness: 10/10 gates PASS (G09 PASS: MTI=100 delta=+14)
+**Snapshot (2026-02-26 S17c):** 31 layers -- 4057 exported objects -- Tests: 41/42 (T36 pre-existing only) -- Readiness: 10/10 gates PASS (G09 PASS: MTI=100) -- MODEL_DIR env override: enables isolated per-project instances (e.g. port 8011 for 51-ACA)
 
 > **Session note (2026-02-26 Session 17 -- brain-v2 housekeeping + evidence batch):**
 >

api/config.py

@@ -1,13 +1,14 @@
 """
-Configuration — loaded from environment variables.
+Configuration -- loaded from environment variables.
 All settings have defaults so the API works with zero config (in-memory mode).
 """
 from __future__ import annotations
+from pydantic import Field
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
 
 class Settings(BaseSettings):
-    model_config = SettingsConfigDict(env_file=".env", env_file_encoding="utf-8", extra="ignore")
+    model_config = SettingsConfigDict(env_file=".env", env_file_encoding="utf-8", extra="ignore", populate_by_name=True)
 
     # --- Cosmos DB (optional — if not set, MemoryStore is used) ---
     cosmos_url: str = ""
@@ -33,10 +34,16 @@ class Settings(BaseSettings):
     # Set DEV_MODE=false in production .env or container environment.
     dev_mode: bool = True
 
-    # Path to the model directory (resolved relative to this file's parent)
+    # Path to the model directory.
+    # Override with MODEL_DIR env var to run an isolated instance pointing at a
+    # different model data folder (e.g. a side project with its own layer JSON files).
+    model_dir_override: str = Field(default="", validation_alias="MODEL_DIR")
+
     @property
     def model_dir(self) -> str:
         from pathlib import Path
+        if self.model_dir_override:
+            return str(Path(self.model_dir_override))
         return str(Path(__file__).parents[1] / "model")
 
     @property

api/routers/admin.py

@@ -88,7 +88,13 @@
     "decisions":       "decisions.json",
 }
 
-_MODEL_DIR = Path(__file__).parents[2] / "model"
+def _get_model_dir() -> Path:
+    """Return the model data directory, honouring MODEL_DIR env override."""
+    from api.config import get_settings
+    override = get_settings().model_dir_override
+    if override:
+        return Path(override)
+    return Path(__file__).parents[2] / "model"
 
 
 # ── SEED ──────────────────────────────────────────────────────────────────────
@@ -112,7 +118,7 @@ async def seed(
     errors: list[str] = []
 
     for layer, filename in _LAYER_FILES.items():
-        path = _MODEL_DIR / filename
+        path = _get_model_dir() / filename
         if not path.exists():
             log.warning("Seed: %s not found, skipping", path)
             continue
@@ -185,7 +191,7 @@ async def export_to_disk(
     _STRIP = {"obj_id", "layer", "_rid", "_self", "_etag", "_attachments", "_ts"}
 
     for layer, filename in _LAYER_FILES.items():
-        path = _MODEL_DIR / filename
+        path = _get_model_dir() / filename
         try:
             objects = await store.get_all(layer, active_only=False)
         except Exception as exc:
@@ -526,7 +532,7 @@ async def commit(
     _STRIP = {"obj_id", "layer", "_rid", "_self", "_etag", "_attachments", "_ts"}
 
     for layer, filename in _LAYER_FILES.items():
-        path = _MODEL_DIR / filename
+        path = _get_model_dir() / filename
         try:
             objects = await store.get_all(layer, active_only=False)
         except Exception as exc:

api/server.py

@@ -126,14 +126,14 @@ async def lifespan(app: FastAPI):
     # object so every record permanently knows which layer file it came from.
     from api.store.memory import MemoryStore as _MS
     if isinstance(store, _MS):
-        from api.routers.admin import _LAYER_FILES, _MODEL_DIR
+        from api.routers.admin import _LAYER_FILES, _get_model_dir
         import json
         total = 0
         for layer, filename in _LAYER_FILES.items():
-            path = _MODEL_DIR / filename
+            path = _get_model_dir() / filename
             if not path.exists():
                 continue
-            raw = json.loads(path.read_text(encoding="utf-8"))
+            raw = json.loads(path.read_text(encoding="utf-8-sig"))
             objects = raw.get(layer, [])
             if not objects:
                 for v in raw.values():
@@ -163,19 +163,19 @@ async def lifespan(app: FastAPI):
         log.info("Shutdown: exporting MemoryStore to disk JSON layer files...")
         try:
             import json as _json
-            from api.routers.admin import _LAYER_FILES, _MODEL_DIR
+            from api.routers.admin import _LAYER_FILES, _get_model_dir
             _STRIP = {"obj_id", "layer", "_rid", "_self", "_etag", "_attachments", "_ts"}
             _total = 0
             for _layer, _filename in _LAYER_FILES.items():
-                _path = _MODEL_DIR / _filename
+                _path = _get_model_dir() / _filename
                 try:
                     _objects = await store.get_all(_layer, active_only=False)
                 except Exception:
                     continue
                 _schema_url = ""
                 if _path.exists():
                     try:
-                        _existing = _json.loads(_path.read_text(encoding="utf-8"))
+                        _existing = _json.loads(_path.read_text(encoding="utf-8-sig"))
                         _schema_url = _existing.get("$schema", "")
                     except Exception:
                         pass