Give the tests one setup instead of thirty-five

Every test module carried the same eight-line prologue redirecting the
database to a temp file. Only the first one to be imported ever took
effect: `app.database` reads `AIDND_DB_PATH` at import and builds `engine`
from it once, so by the time the second module ran the engine already
existed. The other 34 copies created a temp file that nothing opened and
nothing deleted, and leaked one per module per run.

`conftest.py` now does it once, which is early enough because pytest
imports conftest before any test module. It also deletes the file when the
run ends. The tests still share one database, exactly as they already did:
each `client` fixture calls `create_all` on setup and `drop_all` on
teardown, so no test sees another test's rows.

`tests/fakes.py` holds the one `ScriptedProvider`. Nine modules each had a
copy, and the copies had drifted into four feature sets, so a test that
needed to raise a provider error had to be written in one of the files
whose copy supported that. The shared one is the superset. The two
`FakeProvider` copies were the same class with a fixed reply, so they use
it too. `test_chat.py` keeps its own, which implements `chat` rather than
`generate` and records what it was constructed with.

An autouse fixture resets the fake's class state between tests, so a stale
reply list can no longer reach the next test.

435 lines out of the suite. 549 tests pass. Verified live by sabotage:
breaking the shared fake fails 13 tests across four modules.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014Dix4oGV3njgWRdu7P9t6r

backend/tests/test_branch_forking.py

@@ -12,15 +12,6 @@ that makes borrowing possible lives in `lineage`.
 
     python -m pytest tests/test_branch_forking.py -v
 """
-import os
-import tempfile
-
-_tmp = tempfile.NamedTemporaryFile(suffix=".db", delete=False)
-_tmp.close()
-os.environ["AIDND_DB_PATH"] = _tmp.name
-os.environ.pop("AIDND_DATABASE_URL", None)
-os.environ.pop("DATABASE_URL", None)
-
 import pytest
 from fastapi import Depends
 from fastapi.testclient import TestClient
@@ -29,9 +20,10 @@ from app import auth, limits, models
 from app.context import cursors, lineage
 from app.database import Base, SessionLocal, engine, get_db
 from app.main import app
-from app.providers import PromptParts
 from app.routers import adventures
 
+from fakes import ScriptedProvider
+
 # `hp` moves freely. `mana` has a cooldown of 2 turns, so an incorrect
 # advance shows up as a change the referee should have rejected.
 SCHEMA = {
@@ -50,22 +42,6 @@ modifier(text);
 """
 
 
-class ScriptedProvider:
-    last_usage = None
-    replies: list = []
-    calls = 0
-    prompts: list = []
-
-    def __init__(self, *a, **k):
-        pass
-
-    async def generate(self, parts: PromptParts, *, temperature, max_tokens):
-        index = min(ScriptedProvider.calls, len(ScriptedProvider.replies) - 1)
-        ScriptedProvider.calls += 1
-        ScriptedProvider.prompts.append((parts.system, parts.story))
-        yield ("text", ScriptedProvider.replies[index])
-
-
 @pytest.fixture()
 def client(monkeypatch):
     Base.metadata.create_all(bind=engine)