feat(my-deepagent): v0.2 PR #1 — Postgres migration (ahead of M8-Py FastAPI)

Switches the production backing store from SQLite to PostgreSQL 16, per DR-2.
The migration trigger is two concurrent writers on the my-deepagent ORM
tables — which first appears with FastAPI (M8-Py). Doing the cut now keeps
the surface area small while M8-Py is still planning.

Production deps: `asyncpg`, `psycopg[binary]`, `langgraph-checkpoint-postgres`.
Test deps: `aiosqlite` (the bulk of unit + integration tests stay on sqlite
tmp_path for speed; the E2E suite and the new checkpointer tests exercise
the live Postgres path).

Highlights
- `persistence/db.py`: dialect-aware connect listener. SQLite still gets
  WAL + busy_timeout=5000 + foreign_keys=ON; Postgres gets `SET TIME ZONE 'UTC'`.
  Added `Database.dialect_name` + `drop_schema` (test-only).
- `persistence/checkpointer.py`: SqliteSaver → AsyncPostgresSaver. API is
  now async (`async with`) and takes a connection string. SQLAlchemy URL
  prefixes (`+asyncpg`, `+psycopg`) are auto-stripped to a plain libpq DSN
  (`_to_psycopg_dsn` helper, 4 unit tests).
- `persistence/upsert.py` (new): `insert_for(session)` — dialect-aware UPSERT
  helper. Picks `postgresql.insert` or `sqlite.insert` based on the bound
  engine. Replaces 5 hardcoded `sqlite_insert` call sites in `budget.py`,
  `recovery.py`, `cli/doctor.py`.
- `persistence/models.py`: `RunRow` partial unique index declares both
  `postgresql_where=` and `sqlite_where=` for cross-dialect correctness.
- `config.py`: default `database_url` now
  `postgresql+asyncpg://devflow:devflow@localhost:55432/mydeepagent`. v3
  `devflow` DB preserved untouched; v4 lives in a fresh `mydeepagent` DB.
- `cli/doctor.py` check 8: dialect-aware DB liveness probe. Postgres path
  runs `SELECT 1` (pg_isready equivalent); SQLite keeps `PRAGMA integrity_check`.
- `alembic/env.py`: env-aware URL resolution (`MYDEEPAGENT_DATABASE_URL` >
  `DATABASE_URL` > default). Async driver prefixes are mapped to the sync
  equivalents alembic needs.
- `alembic/versions/9f2a6c79667e_v0_2_baseline_schema_postgres.py` (new):
  fresh baseline autogenerated against live Postgres. Old SQLite migrations
  (`79945fdc2649`, `839f2233e346`) deleted — v0.2 starts a clean history.
- `tests/conftest.py` (new): `pg_db_url` async fixture creates a fresh DB
  per test against docker-compose `devflow-postgres` and drops it on
  teardown after terminating lingering backends.
- `tests/integration/test_checkpointer.py`: rewritten for AsyncPostgresSaver
  (4 pure DSN-converter unit tests + 3 async context-manager integration tests).
- `tests/integration/test_e2e_workflow.py`: switched to `pg_db_url`. Real
  OpenRouter E2E now exercises the production Postgres path end-to-end.

Recovery
- Previous SQLite database at the platformdirs data_dir is NOT auto-migrated;
  v0.1.0 was the only release that wrote to it. Set
  `MYDEEPAGENT_DATABASE_URL=sqlite+aiosqlite:///<path>` to read it.
- The v3 `devflow` Postgres DB is preserved untouched (separate database
  name); to inspect: `psql -h localhost -p 55432 -U devflow -d devflow`.

Gates
- ruff check + ruff format --check + mypy --strict: PASS (102 source files)
- pytest non-E2E: 576 PASS (5.46 s)
- pytest E2E real OpenRouter on Postgres: 1 PASS (122.93 s, ~$0.05/run)

--no-verify: lefthook still TS-only (deleted in 0e61b2d but still queryable
in git history).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

my-deepagent/tests/conftest.py

@@ -0,0 +1,80 @@
+"""Test fixtures shared across unit + integration tests.
+
+v0.2 PR #1: tests run against the live Postgres container managed by
+docker-compose. Each test that needs DB isolation requests the
+``pg_db_url`` fixture, which creates a fresh database per test and drops it
+on teardown.
+
+Prerequisites:
+    docker compose up -d postgres      # devflow-postgres on 55432
+"""
+
+from __future__ import annotations
+
+import os
+import uuid
+from collections.abc import AsyncIterator
+from typing import Final
+
+import psycopg
+import pytest_asyncio
+
+# Maintenance connection — used only to CREATE DATABASE / DROP DATABASE.
+# `postgres` is the bootstrap DB present on every Postgres install.
+_MAINTENANCE_DSN: Final[str] = os.environ.get(
+    "MYDEEPAGENT_TEST_MAINTENANCE_DSN",
+    "postgresql://devflow:devflow@localhost:55432/postgres",
+)
+
+
+def _async_url(db_name: str) -> str:
+    """Return the SQLAlchemy + asyncpg URL for *db_name*."""
+    return f"postgresql+asyncpg://devflow:devflow@localhost:55432/{db_name}"
+
+
+def _create_test_database() -> str:
+    """Create a fresh test database with a random suffix and return its name."""
+    db_name = f"test_{uuid.uuid4().hex[:16]}"
+    # autocommit=True is required for CREATE DATABASE (cannot run in a tx block).
+    with psycopg.connect(_MAINTENANCE_DSN, autocommit=True) as conn:
+        with conn.cursor() as cur:
+            cur.execute(f'CREATE DATABASE "{db_name}"')
+    return db_name
+
+
+def _drop_test_database(db_name: str) -> None:
+    """Forcefully terminate connections and drop *db_name*. Idempotent."""
+    with psycopg.connect(_MAINTENANCE_DSN, autocommit=True) as conn:
+        with conn.cursor() as cur:
+            # Kick any lingering connections held by aiosqlite-style pools that
+            # didn't dispose cleanly. WITH (FORCE) is Postgres 13+.
+            cur.execute(
+                """
+                SELECT pg_terminate_backend(pid)
+                FROM pg_stat_activity
+                WHERE datname = %s AND pid <> pg_backend_pid()
+                """,
+                (db_name,),
+            )
+            cur.execute(f'DROP DATABASE IF EXISTS "{db_name}"')
+
+
+@pytest_asyncio.fixture
+async def pg_db_url() -> AsyncIterator[str]:
+    """Yield an isolated Postgres database URL; drop the DB on teardown.
+
+    Usage::
+
+        async def test_something(pg_db_url: str) -> None:
+            db = Database(pg_db_url)
+            await db.init_schema()
+            ...
+
+    The returned URL uses the asyncpg driver. To get a sync URL for tools
+    like alembic, replace ``postgresql+asyncpg://`` with ``postgresql+psycopg://``.
+    """
+    db_name = _create_test_database()
+    try:
+        yield _async_url(db_name)
+    finally:
+        _drop_test_database(db_name)