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DRU-1149 -- SPA fallback breaks on FastAPI 0.162: Accept: */* no longer serves index.html #1169

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Merged
czpython merged 1 commit into from
Nov 10, 2026
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DRU-1149 -- SPA fallback breaks on FastAPI 0.162: Accept: */* no longer serves index.html #1169

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11 changes: 6 additions & 5 deletions backend/druks/api/server.py
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Original file line number Diff line number Diff line change
Expand Up @@ -376,11 +376,12 @@ async def mcp_not_found(path: str) -> None:


def serve_spa(app: FastAPI, dist: Path = _SPA_DIST) -> None:
"""Serve the platform's own dashboard the way an app's ``dist/`` is
served — FastAPI's low-priority frontend routes, so every API path (and every
app frontend, registered earlier) wins, and unknown paths fall back to
index.html for client-side routing. A bare pip install ships no SPA build;
then the API serves JSON only."""
"""Serve the platform's own dashboard the way Druks serves an app's ``dist/``.
FastAPI serves both from low-priority frontend routes. Every API path wins over
them. Every app frontend registers earlier and also wins. An unknown path falls
back to index.html for client-side routing. The index.html fallback needs a
navigation request with an ``Accept: text/html`` header. A bare pip install
ships no SPA build. Without a build, the API serves JSON only."""
if (dist / "index.html").is_file():
app.frontend("/", directory=dist)

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10 changes: 6 additions & 4 deletions backend/tests/test_spa_serving.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
from druks.db import db_session
from fastapi import Depends, FastAPI, HTTPException
from fastapi.testclient import TestClient
from sqlalchemy.orm import Session


def _app_with_spa(dist: Path) -> FastAPI:
Expand All @@ -30,7 +31,7 @@ def test_spa_serves_index_assets_and_client_routes(tmp_path):
assert "druks" in client.get("/").text
assert client.get("/assets/app.js").status_code == 200
# An unknown path is a client-side route: index.html, not a 404.
assert "druks" in client.get("/work_items/42").text
assert "druks" in client.get("/work_items/42", headers={"Accept": "text/html"}).text


def test_api_paths_win_over_the_spa(tmp_path):

@druks-ai druks-ai Bot Nov 10, 2026

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medium. After the 0.162 bump, this test passes without the code it protects. TestClient sends Accept: */*. On 0.162, FastAPI never serves the index.html fallback for that header. So /api/nope returns 404 whether the /api/{path:path} catch-all exists or not.

I checked this: I deleted api_not_found from _app_with_spa and ran the file. On 0.139.0, this test fails, as it should. On 0.162.0, all 5 tests pass. The case the catch-all protects, which the comment on line 40 describes, is a browser navigation to an unknown /api/* path. Line 41 needs the same header as the client-route requests:

assert client.get("/api/nope", headers={"Accept": "text/html"}).status_code == 404

This goes past AC2, which kept this test unchanged. But it has the same cause and the same fix as AC1, and review.md item 14 requires a test to fail when the code it guards is gone. With the header, the test fails without the catch-all on both 0.139 and 0.162.

Expand All @@ -55,15 +56,16 @@ def test_cache_policy_lives_with_the_server(tmp_path):
assert asset.headers["cache-control"] == "public, max-age=31536000, immutable"
# index.html must revalidate every load or a deploy leaves stale bundles.
assert client.get("/").headers["cache-control"] == "no-cache"
assert client.get("/work_items/42").headers["cache-control"] == "no-cache"
assert (
client.get("/work_items/42", headers={"Accept": "text/html"}).headers["cache-control"]
== "no-cache"
)
# API responses carry no frontend cache policy; nor does a missing asset.
assert "cache-control" not in client.get("/api/thing").headers
assert "cache-control" not in client.get("/assets/gone.js").headers


def test_request_that_never_touches_the_db_opens_no_connection(monkeypatch):
from sqlalchemy.orm import Session

connected = []
original = Session._connection_for_bind

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