check-latest: true, add 3.15 to test matrix, to test RCs (#2895)

See https://simonwillison.net/2026/Sep/1/python-315-rc-2/

.github/workflows/test.yml

@@ -11,16 +11,17 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14", "3.15"]
     steps:
     - uses: actions/checkout@v7
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v6
+      uses: actions/setup-python@v7
       with:
         python-version: ${{ matrix.python-version }}
         allow-prereleases: true
         cache: pip
         cache-dependency-path: pyproject.toml
+        check-latest: true
     - name: Build extension for --load-extension test
       run: |-
         (cd tests && gcc ext.c -fPIC -shared -o ext.so)

datasette/cli.py

@@ -670,11 +670,9 @@ def serve(
         raise click.ClickException("--token can only be used with --get")
 
     if get:
-        # Run async soundness checks before startup hooks, since invoke_startup
-        # now populates internal tables which requires querying each database
+        # --get means we don't run Uvicorn at all
         run_sync(lambda: check_databases(ds))
 
-        # Run the "startup" plugin hooks
         try:
             run_sync(ds.invoke_startup)
         except StartupError as e:
@@ -709,8 +707,7 @@ def serve(
     # on the loop (asyncio.create_task, Lock/Queue/Event objects, ...) is
     # still alive when the server starts handling requests.
     async def _serve_async():
-        # Run async soundness checks before startup hooks, since invoke_startup
-        # now populates internal tables which requires querying each database
+        # Populate internal catalog tables before invoke_startup
         await check_databases(ds)
 
         # Run the full startup sequence (immutable-database table-count

tests/test_cli_serve_server.py

@@ -127,11 +127,6 @@ def test_startup_error_fails_fast_before_port_binds(serve_with_plugins):
     A "startup" plugin hook that raises StartupError must fail fast: print
     the message, exit non-zero, and never accept a connection on the port -
     the failure must happen before uvicorn.Server binds the socket.
-
-    Note this is a characterization test, not a regression test: it also
-    passes on unmodified main, where startup already ran ahead of
-    uvicorn.run(). It earns its keep once startup moves into the ASGI
-    lifespan, where fail-fast is genuinely at risk.
     """
     proc, port = serve_with_plugins(
         {"startup_error_plugin": STARTUP_ERROR_PLUGIN}, wait_for_startup=False