feat(slice-2): deps — mailer + session dependencies; build mailer at startup

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/main.py

@@ -1,19 +1,62 @@
 """ecomm backend — FastAPI app factory + the REST BFF.
 
-SLICE-1 mounts only /healthz; the auth and storefront endpoints (§6.4) grow here in
+SLICE-1 mounted /healthz; SLICE-2 adds the /api/auth/* identity endpoints (§6.4). The BFF
-later slices. create_app() opens the connection pool and self-migrates the database
+translates HTTP <-> domain calls and owns no business logic (INV-6): every rule lives in
-at startup (INV-1, INV-7): the app boots against empty persistence and applies its
+the accounts domain. create_app() opens the pool, self-migrates (INV-1, INV-7), and builds
-own schema — there is no seed step.
+the configured mailer (INV-8) at startup. storefront is hard-wired null this slice; the
+storefronts domain (SLICE-3) replaces the _storefront_for seam.
 """
 from __future__ import annotations
 
 from contextlib import asynccontextmanager
+from typing import Any
 
 import psycopg
 from fastapi import Depends, FastAPI, Response
+from fastapi.responses import JSONResponse
+from pydantic import BaseModel
 
+from app.domains import accounts
 from app.platform import config, db
-from app.platform.deps import get_conn
+from app.platform import mailer as mailer_mod
+from app.platform.deps import SESSION_COOKIE, get_conn, get_mailer, get_session
+from app.platform.mailer import Mailer
+from app.platform import session as session_mod
+
+
+class RequestCodeBody(BaseModel):
+    email: str
+
+
+class VerifyBody(BaseModel):
+    email: str
+    code: str
+
+
+def _error(status: int, code: str, message: str, **extra: Any) -> JSONResponse:
+    """The shared §6.4 error envelope: {"error": {"code", "message", ...}}."""
+    return JSONResponse(status_code=status, content={"error": {"code": code, "message": message, **extra}})
+
+
+def _storefront_for(conn: psycopg.Connection, account: accounts.Account) -> dict | None:
+    """The entry-routing answer: which storefront, if any, this account has (§6.5).
+
+    Hard-wired null in SLICE-2 (identity only). SLICE-3 replaces this with a storefronts
+    domain call; the verify/me responses already carry the field.
+    """
+    return None
+
+
+def _set_session_cookie(response: Response, account: accounts.Account) -> None:
+    token = session_mod.sign({"account_id": account.id, "email": account.email}, config.session_secret())
+    response.set_cookie(
+        SESSION_COOKIE,
+        token,
+        httponly=True,
+        samesite="lax",
+        secure=config.cookie_secure(),
+        path="/",
+    )
 
 
 def create_app(database_url: str | None = None) -> FastAPI:
@@ -24,12 +67,13 @@ def create_app(database_url: str | None = None) -> FastAPI:
         app.state.pool = db.open_pool(dsn)
         with app.state.pool.connection() as conn:
             db.migrate(conn)  # self-migrate at startup (INV-1, INV-7)
+        app.state.mailer = mailer_mod.build_mailer(config.mailer_kind())  # INV-8
         try:
             yield
         finally:
             app.state.pool.close()
 
-    app = FastAPI(title="ecomm", version="0.1", lifespan=lifespan)
+    app = FastAPI(title="ecomm", version="0.2", lifespan=lifespan)
 
     @app.get("/healthz")
     def healthz(response: Response, conn: psycopg.Connection = Depends(get_conn)):
@@ -45,6 +89,67 @@ def create_app(database_url: str | None = None) -> FastAPI:
             return {"status": "unavailable", "reason": "migrations_pending"}
         return {"status": "ok"}
 
+    @app.post("/api/auth/request-code")
+    def request_code(
+        body: RequestCodeBody,
+        conn: psycopg.Connection = Depends(get_conn),
+        mailer: Mailer = Depends(get_mailer),
+    ):
+        """Issue + dispatch a one-time code. Uniform for new/known emails (§6.6)."""
+        try:
+            accounts.request_code(conn, mailer, body.email)
+        except accounts.InvalidEmail:
+            return _error(400, "invalid_email", "That doesn't look like an email address.")
+        except accounts.ResendCooldown as exc:
+            return _error(
+                429, "resend_cooldown",
+                f"Please wait {exc.retry_after_s}s before requesting another code.",
+                retry_after_s=exc.retry_after_s,
+            )
+        return Response(status_code=204)
+
+    @app.post("/api/auth/verify")
+    def verify(body: VerifyBody, conn: psycopg.Connection = Depends(get_conn)):
+        """Verify a code, start a session, and answer entry routing (§6.4/§6.5)."""
+        try:
+            account, created = accounts.verify(conn, body.email, body.code)
+        except accounts.InvalidEmail:
+            return _error(400, "invalid_email", "That doesn't look like an email address.")
+        except accounts.CodeMismatch as exc:
+            return _error(
+                400, "code_mismatch", "That code didn't match.",
+                attempts_remaining=exc.attempts_remaining,
+            )
+        except accounts.CodeExpired:
+            return _error(400, "code_expired", "That code expired — request a fresh one.")
+        except accounts.CodeExhausted:
+            return _error(400, "code_exhausted", "Too many attempts — request a fresh code.")
+        payload = {
+            "account": {"email": account.email},
+            "storefront": _storefront_for(conn, account),
+            "created": created,
+        }
+        resp = JSONResponse(status_code=200, content=payload)
+        _set_session_cookie(resp, account)
+        return resp
+
+    @app.get("/api/auth/me")
+    def me(conn: psycopg.Connection = Depends(get_conn), sess: dict | None = Depends(get_session)):
+        """The signed-in account + entry-routing answer, or 401 (§6.4/§6.5)."""
+        if sess is None:
+            return _error(401, "unauthenticated", "You are not signed in.")
+        account = accounts.get_account(conn, sess["account_id"])
+        if account is None:
+            return _error(401, "unauthenticated", "You are not signed in.")
+        return {"account": {"email": account.email}, "storefront": _storefront_for(conn, account)}
+
+    @app.post("/api/auth/logout")
+    def logout():
+        """End the session by clearing the cookie. Idempotent (PUC-9; no server state)."""
+        resp = Response(status_code=204)
+        resp.delete_cookie(SESSION_COOKIE, path="/")
+        return resp
+
     return app
 
 

backend/app/platform/deps.py

@@ -1,18 +1,38 @@
 """FastAPI dependencies — per-request wiring (SD-0001 §6.2 platform/deps).
 
-Yields a pooled connection per request. The pool lives on app.state, built once in
+Yields a pooled connection per request, the process-wide mailer, and the verified session
-create_app(). Later slices add the current-session and mailer dependencies here.
+payload (from the signed cookie). The pool and mailer live on app.state, built once in
+create_app(). The storefronts dependency lands in SLICE-3.
 """
 from __future__ import annotations
 
 from collections.abc import Iterator
+from typing import Any
 
 import psycopg
 from fastapi import Request
 
+from app.platform import config, session
+from app.platform.mailer import Mailer
+
+SESSION_COOKIE = "ecomm_session"
+
 
 def get_conn(request: Request) -> Iterator[psycopg.Connection]:
     """A pooled connection for the duration of one request."""
     pool = request.app.state.pool
     with pool.connection() as conn:
         yield conn
+
+
+def get_mailer(request: Request) -> Mailer:
+    """The process-wide mailer adapter (built from config at startup, INV-8)."""
+    return request.app.state.mailer
+
+
+def get_session(request: Request) -> dict[str, Any] | None:
+    """The verified session payload from the cookie, or None if absent/invalid."""
+    token = request.cookies.get(SESSION_COOKIE)
+    if not token:
+        return None
+    return session.verify(token, config.session_secret())