Create a new app silently fails with 404

[SeanningTatum]

Summary: Clicking "Create" in the "Create a new app" dialog POSTs to /dev/apps/{name}/builder/save?tmp=true, which returns 404 Not Found when adk web falls back to ApiServer. The UI dismisses the dialog with no error feedback and the app is never created.

Steps to Reproduce

1. Run adk web (without python-multipart installed)
2. Click the app selector dropdown
3. Click the + ("Create new agent") button
4. Enter a valid app name (e.g. my_test_app)
5. Click Create

Expected Behavior

New app scaffold is created and the builder opens for my_test_app.

Actual Behavior

Dialog dismisses silently. No app is created. Browser console shows:

Failed to load resource: the server responded with a status of 404 (Not Found)

Network trace:
POST /dev/apps/my_test_app/builder/save?tmp=true → 404 {"detail": "Not Found"}

Additionally, on every page load while an app is selected:
GET /dev/apps/{app}/build_graph → 404
GET /dev/apps/{app}/build_graph_image?dark_mode=false → 404
GET /dev/apps/{app}/build_graph_image?dark_mode=true → 404
GET /dev/apps/{app}/builder?ts=... → 404
GET /dev/apps/{app}/eval_sets → 404
GET /dev/apps/{app}/eval_results → 404

Server startup log emits:
WARNING - DevServer not found, falling back to ApiServer. Dev-only endpoints will not be available.
WARNING - python-multipart not installed. Builder UI endpoints will not be available.

Screenshots

Environment

google-adk	2.0.0
Python	3.12.12
OS	macOS Darwin 24.2.0
Command	uv run adk web

[SeanningTatum]

Root cause identified

DevServer (which registers all /dev/ endpoints) fails to import silently and falls back to ApiServer — which has none of those routes, hence the 404s.

The import chain:

dev_server.py
  → utils/evals.py
    → evaluation/gcs_eval_set_results_manager.py
      → google.cloud.exceptions   ← ImportError: google-cloud-core not installed
      → google.cloud.storage      ← ImportError: google-cloud-storage not installed

Workaround

uv add google-cloud-core google-cloud-storage
# or: pip install google-cloud-core google-cloud-storage

After installing both, DevServer imports correctly and all /dev/ endpoints work as expected.

Reproduction path

Created project with adk create and followed the quickstart docs. Neither google-cloud-core nor google-cloud-storage are installed by default — and the fallback to ApiServer is silent (warning only in server logs, not surfaced in the UI), so the 404s are the only indication something is wrong.