feat: expose recommendation streaming api

backend/app/api/routes.py

@@ -1,5 +1,6 @@
 """HTTP routes for Spotify login and session management."""
 
+from dataclasses import dataclass
 from typing import cast
 
 import httpx2
@@ -7,7 +8,7 @@ from fastapi import APIRouter, Request
 from fastapi.responses import JSONResponse, RedirectResponse, Response
 
 from app.adapters.spotify.login import begin_login, complete_login
-from app.adapters.spotify.session import PendingLogins, SessionStore
+from app.adapters.spotify.session import PendingLogins, SessionStore, SpotifySession
 from app.config import Settings
 
 SESSION_COOKIE_NAME = "discovery_session"
@@ -15,6 +16,14 @@ SESSION_COOKIE_NAME = "discovery_session"
 router = APIRouter()
 
 
+@dataclass(frozen=True)
+class ResolvedSession:
+    """A session and stable cache key selected for one request."""
+
+    session_id: str
+    session: SpotifySession
+
+
 @router.get("/api/auth/login")
 def login(request: Request) -> RedirectResponse:
     """Start Spotify Authorization Code with PKCE login."""
@@ -65,12 +74,10 @@ async def callback(
 @router.get("/api/auth/me")
 def current_session(request: Request) -> JSONResponse:
     """Return the display name for a valid application session."""
-    session_id = request.cookies.get(SESSION_COOKIE_NAME)
-    session_store = cast(SessionStore, request.app.state.session_store)
-    session = session_store.get(session_id) if session_id is not None else None
-    if session is None:
+    resolved = resolve_session(request)
+    if resolved is None:
         return JSONResponse({"detail": "Not authenticated"}, status_code=401)
-    return JSONResponse({"display_name": session.display_name})
+    return JSONResponse({"display_name": resolved.session.display_name})
 
 
 @router.post("/api/auth/logout", status_code=204)
@@ -95,3 +102,19 @@ def logout(request: Request) -> Response:
 
 def _login_error_redirect() -> RedirectResponse:
     return RedirectResponse("/?login=error", status_code=307)
+
+
+def resolve_session(request: Request) -> ResolvedSession | None:
+    """Resolve the cookie session or the installed live seed session."""
+    session_store = cast(SessionStore, request.app.state.session_store)
+    cookie_session_id = request.cookies.get(SESSION_COOKIE_NAME)
+    if cookie_session_id is not None:
+        cookie_session = session_store.get(cookie_session_id)
+        if cookie_session is not None:
+            return ResolvedSession(cookie_session_id, cookie_session)
+
+    seed_session_id = cast(str | None, getattr(request.app.state, "seed_session_id", None))
+    seed_session = session_store.get(seed_session_id) if seed_session_id is not None else None
+    if seed_session is None or seed_session_id is None:
+        return None
+    return ResolvedSession(seed_session_id, seed_session)