Stage 5: Alembic migrations, durable call rows, one transcript truth

Alembic replaces create_all as the schema authority: async env.py
against Base.metadata (CLI and in-app entry paths share it via
config.attributes["connection"]), an autogenerated baseline of the
create_all-era schema, and init_db now runs upgrade head — stamping
the baseline first on a pre-Alembic database so existing deployments
adopt cleanly. create_all remains for tests only.

Calls are durable from the start: CallManager gains an
on_call_created hook (wired to persist_call_on_create) that inserts
an in_progress CallRecord the moment a call is created;
persist_call_on_end finalizes that same row. A SIGKILL mid-call now
leaves an in_progress row instead of erasing the call from history
(verified live against the dev database).

One transcript representation: ActiveCall.transcript_chunks holds
TranscriptEntry (t_offset_ms, speaker, text) — add_transcript stamps
real offsets from connect time, receptionist passes speaker instead
of encoding it into "caller: ..." strings, persisted chunks carry
real seek offsets, and the dead CallRecord.transcript Text column is
dropped by migration. Device.is_online migrates String → Boolean
(with a USING cast for existing rows).

Model de-triplication: CallResponse/CallStatusResponse build via
from_call classmethods (one ActiveCall→response mapping);
DeviceStatus deleted — can_receive_call is a computed field on
Device and the list endpoint returns the domain model; all row↔dict
and row↔domain mapping now lives in call_persistence.py
(record_summary/record_detail/chunk_to_dict + device row functions).

New tests/test_data_layer.py: upgrade-head-matches-models,
pre-Alembic adoption, durable in_progress rows, end-without-create
fallback, transcript offsets, consolidated response models.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

db/migrations/env.py

@@ -0,0 +1,68 @@
+"""
+Alembic environment — async engine against Base.metadata.
+
+Two entry paths:
+- CLI (``alembic upgrade head``): builds an async engine from
+  Settings.database_url and runs migrations on it.
+- App startup (db.database.init_db): passes an already-open
+  connection via ``config.attributes["connection"]`` so migrations
+  run inside the app's engine instead of opening a second one.
+"""
+
+import asyncio
+from logging.config import fileConfig
+
+from alembic import context
+from sqlalchemy import pool
+from sqlalchemy.ext.asyncio import create_async_engine
+
+from config import get_settings
+from db.database import Base
+
+config = context.config
+
+# Only configure logging on standalone CLI runs — inside the app this
+# would clobber uvicorn's logger setup.
+if config.config_file_name is not None and config.attributes.get("connection") is None:
+    fileConfig(config.config_file_name, disable_existing_loggers=False)
+
+target_metadata = Base.metadata
+
+
+def run_migrations_offline() -> None:
+    """Emit SQL to stdout without a live connection (--sql mode)."""
+    context.configure(
+        url=get_settings().database_url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def do_run_migrations(connection) -> None:
+    context.configure(connection=connection, target_metadata=target_metadata)
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+async def run_async_migrations() -> None:
+    engine = create_async_engine(get_settings().database_url, poolclass=pool.NullPool)
+    async with engine.connect() as connection:
+        await connection.run_sync(do_run_migrations)
+    await engine.dispose()
+
+
+def run_migrations_online() -> None:
+    connection = config.attributes.get("connection")
+    if connection is not None:
+        do_run_migrations(connection)
+    else:
+        asyncio.run(run_async_migrations())
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()