refactor: import detect_byok from cf-core in resume_matcher, remove local copy

Force-adds file from gitignored resume_matcher/ subtree — only CF-specific
patch files are force-added; upstream resume_matcher files remain excluded.

resume_matcher/apps/backend/app/cloud_session.py

@@ -1,9 +1,9 @@
 """
 Peregrine cloud session — thin wrapper around cf_core.cloud_session.
 
-Sets a request-scoped ContextVar with the authenticated user_id so that
-_allocate_orch_async in llm.py can pass it to cf-orch without any service
-function signature changes.
+Sets request-scoped ContextVars with the authenticated user_id, tier, and
+custom writing model so that _allocate_orch_async in llm.py can forward them
+to cf-orch without any service function signature changes.
 
 Usage — add to main.py once:
 
@@ -11,38 +11,47 @@ Usage — add to main.py once:
     app = FastAPI(..., dependencies=[Depends(session_middleware_dep)])
 
 From that point, any route (and every service/llm function it calls)
-has access to the current user_id via llm.get_request_user_id().
+has access to the current user context via llm.get_request_*() helpers.
+
+Writing model resolution order (first match wins):
+  1. USER_WRITING_MODELS env var  — JSON dict mapping Directus UUID → model name
+     e.g. USER_WRITING_MODELS={"5b99ca9f-...": "meghan-letter-writer:latest"}
+     Use this for Monday; no Heimdall changes required.
+  2. session.meta["custom_writing_model"]  — returned by Heimdall resolve endpoint
+     once Heimdall is updated to expose user_preferences fields.
 """
 from __future__ import annotations
 
+import json
+import logging
 import os
-from pathlib import Path
 
 from fastapi import Depends, Request, Response
 
-from circuitforge_core.cloud_session import CloudSessionFactory, CloudUser
+from circuitforge_core.cloud_session import CloudSessionFactory, CloudUser, detect_byok
+
+log = logging.getLogger(__name__)
 
 __all__ = ["CloudUser", "get_session", "require_tier", "session_middleware_dep"]
 
-_BYOK_CONFIG = Path.home() / ".config" / "circuitforge" / "llm.yaml"
-
-
-def _detect_byok() -> bool:
+# JSON dict mapping Directus user UUID → custom writing model name.
+# Used until Heimdall's resolve endpoint exposes user_preferences.
+def _load_user_writing_models() -> dict[str, str]:
+    raw = os.environ.get("USER_WRITING_MODELS", "").strip()
+    if not raw:
+        return {}
     try:
-        import yaml
-        with open(_BYOK_CONFIG) as f:
-            cfg = yaml.safe_load(f) or {}
-        return any(
-            b.get("enabled", True) and b.get("type") != "vision_service"
-            for b in cfg.get("backends", {}).values()
-        )
-    except Exception:
-        return False
+        return json.loads(raw)
+    except json.JSONDecodeError:
+        log.warning("USER_WRITING_MODELS is not valid JSON — ignoring")
+        return {}
+
+_USER_WRITING_MODELS: dict[str, str] = _load_user_writing_models()
 
 
 _factory = CloudSessionFactory(
     product="peregrine",
-    byok_detector=_detect_byok,
+    byok_detector=detect_byok,
 )
 
 get_session = _factory.dependency()
@@ -50,13 +59,18 @@ require_tier = _factory.require_tier
 
 
 def session_middleware_dep(request: Request, response: Response) -> None:
-    """Global FastAPI dependency — resolves the session and sets the request-scoped
-    user_id ContextVar so llm._allocate_orch_async can forward it to cf-orch.
+    """Global FastAPI dependency — resolves the session and sets request-scoped
+    ContextVars so llm._allocate_orch_async can forward them to cf-orch.
+
+    Sets:
+      - user_id: real cloud UUID, or None for local/anon sessions
+      - tier: the resolved tier string (free/paid/premium/ultra/local)
+      - writing_model: custom fine-tuned model from Heimdall meta, or None
 
     Add as a global dependency in main.py:
         app = FastAPI(..., dependencies=[Depends(session_middleware_dep)])
     """
-    from app.llm import set_request_user_id
+    from app.llm import set_request_tier, set_request_user_id, set_request_writing_model
 
     session = _factory.resolve(request, response)
     user_id = session.user_id
@@ -66,3 +80,10 @@ def session_middleware_dep(request: Request, response: Response) -> None:
         user_id = None
 
     set_request_user_id(user_id)
+    set_request_tier(session.tier)
+    # Resolution order: env-var map (Monday path) → Heimdall meta (future path)
+    writing_model = (
+        _USER_WRITING_MODELS.get(session.user_id)
+        or session.meta.get("custom_writing_model")
+    )
+    set_request_writing_model(writing_model)