tests: extract _build_session_factory to a shared conftest fixture

The same per-test sqlite-engine setup was duplicated across 14 test
files (~30 lines each). Consolidated into a single async fixture
`db_factory` in tests/conftest.py; tests now take db_factory as a
parameter and use `async with db_factory() as session` directly.

No behaviour change — same function-scope, same in-memory schema
created via Base.metadata.create_all, same app.db._engine /
_session_factory rebinding so module-level helpers see the test
engine. Just ~420 lines of boilerplate removed.

tests/test_localization_integration.py

@@ -5,25 +5,6 @@ from __future__ import annotations
 import pytest
 
 
-def _build_session_factory(tmp_path):
-    """Per-test sqlite engine + factory. Mirrors test_referral_conversion.py."""
-    from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
-
-    from app import db as db_mod
-    from app.db import Base
-    import app.models  # noqa: F401 — registers models on Base.metadata
-
-    engine = create_async_engine(f"sqlite+aiosqlite:///{tmp_path}/loc.db")
-    factory = async_sessionmaker(engine, expire_on_commit=False)
-    db_mod._engine = engine
-    db_mod._session_factory = factory
-
-    async def _setup():
-        async with engine.begin() as conn:
-            await conn.run_sync(Base.metadata.create_all)
-
-    return engine, factory, _setup
-
 
 def test_user_has_lang_column_with_default_en():
     from sqlalchemy import inspect
@@ -55,7 +36,7 @@ def test_strategic_log_translation_model_columns():
     assert cols["content_md"].nullable is False
 
 
-async def test_log_translation_fanout_no_active_non_en_users(tmp_path, monkeypatch):
+async def test_log_translation_fanout_no_active_non_en_users(db_factory, monkeypatch):
     """When no users have an active non-en lang, the fan-out makes no
     translation calls and no rows are inserted."""
     from unittest.mock import AsyncMock
@@ -65,8 +46,7 @@ async def test_log_translation_fanout_no_active_non_en_users(tmp_path, monkeypat
     from app.models import StrategicLog, StrategicLogTranslation, User
     from app.jobs import ai_log_job
 
-    _, factory, setup = _build_session_factory(tmp_path)
-    await setup()
+    factory = db_factory
 
     fake_translate = AsyncMock()
     monkeypatch.setattr(ai_log_job, "translate", fake_translate)
@@ -92,7 +72,7 @@ async def test_log_translation_fanout_no_active_non_en_users(tmp_path, monkeypat
     assert rows == []
 
 
-async def test_log_translation_fanout_italian_user(tmp_path, monkeypatch):
+async def test_log_translation_fanout_italian_user(db_factory, monkeypatch):
     """One user at lang=it triggers one translation; the row lands with
     the right lang and log_id."""
     from sqlalchemy import select
@@ -102,8 +82,7 @@ async def test_log_translation_fanout_italian_user(tmp_path, monkeypatch):
     from app.services.openrouter import LogResult
     from app.jobs import ai_log_job
 
-    _, factory, setup = _build_session_factory(tmp_path)
-    await setup()
+    factory = db_factory
 
     async def _fake_translate(client, text, target_lang):
         assert target_lang == "it"
@@ -139,7 +118,7 @@ async def test_log_translation_fanout_italian_user(tmp_path, monkeypatch):
     assert row.llm_cost_usd == pytest.approx(0.00002)
 
 
-async def test_log_translation_fanout_per_language_failure_isolated(tmp_path, monkeypatch):
+async def test_log_translation_fanout_per_language_failure_isolated(db_factory, monkeypatch):
     """If one language's translation fails, the others (if any) still land
     and the job does not raise."""
     from sqlalchemy import select
@@ -148,8 +127,7 @@ async def test_log_translation_fanout_per_language_failure_isolated(tmp_path, mo
     from app.models import StrategicLog, StrategicLogTranslation, User
     from app.jobs import ai_log_job
 
-    _, factory, setup = _build_session_factory(tmp_path)
-    await setup()
+    factory = db_factory
 
     async def _fake_translate(client, text, target_lang):
         raise RuntimeError("upstream down")
@@ -175,7 +153,7 @@ async def test_log_translation_fanout_per_language_failure_isolated(tmp_path, mo
     assert rows == []
 
 
-async def test_analyse_threads_lang_into_system_prompt(tmp_path, monkeypatch):
+async def test_analyse_threads_lang_into_system_prompt(db_factory, monkeypatch):
     """When lang='it', the system prompt sent to call_llm contains
     'Respond in Italian.' — the LLM does the rest."""
     from app.services import portfolio_analysis as pa
@@ -191,8 +169,7 @@ async def test_analyse_threads_lang_into_system_prompt(tmp_path, monkeypatch):
         )
     monkeypatch.setattr(pa, "call_llm", _fake_call_llm)
 
-    _, factory, setup = _build_session_factory(tmp_path)
-    await setup()
+    factory = db_factory
 
     payload = {
         "positions": [{"yahoo_ticker": "AAPL", "qty": 10, "avg_cost": 150.0,
@@ -213,7 +190,7 @@ async def test_analyse_threads_lang_into_system_prompt(tmp_path, monkeypatch):
     assert "Respond in Italian" in system
 
 
-async def test_analyse_no_clause_when_lang_is_en(tmp_path, monkeypatch):
+async def test_analyse_no_clause_when_lang_is_en(db_factory, monkeypatch):
     from app.services import portfolio_analysis as pa
     from app.services.openrouter import LogResult
 
@@ -227,8 +204,7 @@ async def test_analyse_no_clause_when_lang_is_en(tmp_path, monkeypatch):
         )
     monkeypatch.setattr(pa, "call_llm", _fake_call_llm)
 
-    _, factory, setup = _build_session_factory(tmp_path)
-    await setup()
+    factory = db_factory
 
     payload = {
         "positions": [{"yahoo_ticker": "AAPL", "qty": 10, "avg_cost": 150.0,
@@ -328,13 +304,12 @@ def test_digest_pick_variant_uses_user_lang():
 
 
 
-async def test_patch_language_accepts_active(tmp_path):
+async def test_patch_language_accepts_active(db_factory):
     """PATCH /api/settings/language accepts 'en' and 'it' and persists."""
     from app.models import User
     from app.routers.api import patch_language_prefs, LanguagePrefsIn
 
-    _, factory, setup = _build_session_factory(tmp_path)
-    await setup()
+    factory = db_factory
 
     async with factory() as session:
         session.add(User(id=20, email="u@x", tier="paid", lang="en"))
@@ -358,14 +333,13 @@ async def test_patch_language_accepts_active(tmp_path):
     assert user.lang == "it"
 
 
-async def test_patch_language_rejects_wip(tmp_path):
+async def test_patch_language_rejects_wip(db_factory):
     """PATCH rejects 'es'/'fr'/'de'/'xx' with 400 — ACTIVE_LANGUAGES gate."""
     from fastapi import HTTPException
     from app.models import User
     from app.routers.api import patch_language_prefs, LanguagePrefsIn
 
-    _, factory, setup = _build_session_factory(tmp_path)
-    await setup()
+    factory = db_factory
 
     async with factory() as session:
         session.add(User(id=21, email="u2@x", tier="paid", lang="en"))