feat: enable parallel pytest-xdist test execution with isolated per-worker databases and data directories

CLAUDE.md

@@ -13,8 +13,10 @@ make install        # pip install -e .
 make ppy            # build the single shared container image (ppy:latest); run once before launching instances
 make dev            # uvicorn --reload on port 10500
 make prod           # uvicorn 2 workers, port 10500 (backlog 8192)
-make test           # Playwright + unit tests, headless, -x fail-fast
-make test-headed    # same tests in visible browser
+make test           # Playwright + unit tests, headless, parallel (pytest-xdist -n auto, distributed per file), -x fail-fast
+make test-serial    # same tests in a single process (no xdist) for debugging
+make test-headed    # same tests in visible browsers, parallel (one Chromium window per worker)
+make test-headed-serial  # visible browser, single process (one window) for debugging
 make locust         # Locust load test, interactive web UI
 make locust-headless  # Locust CLI mode for CI
 ```
@@ -44,7 +46,7 @@ devplace containers prune-builds  # remove legacy per-project images + clear doc
 devplace containers gc-workspaces  # remove workspace dirs with no instances
 ```
 
-Tests run on ports 10501+ (xdist worker offset) with a tempfile SQLite DB and `DEVPLACE_DISABLE_SERVICES=1` so background services don't start.
+Tests run on ports 10501+ (xdist worker offset) with a per-worker tempfile SQLite DB and a per-worker `DEVPLACE_DATA_DIR` (both keyed off `_xdist_port()`), and `DEVPLACE_DISABLE_SERVICES=1` so background services don't start. `make test` runs in parallel via pytest-xdist (`-n auto --dist loadfile`): each worker is one isolated DB + data dir + uvicorn subprocess + Chromium, and `loadfile` pins all tests in a file to one worker so session fixtures (`seeded_db`) and intra-file ordering hold. Override worker count with `make test TEST_WORKERS=4` (default `auto` = one per core); use `make test-serial` for single-process debugging.
 
 ## Environment variables