Description

Fixes #1450.

ListTasks with DatabaseTaskStore returns HTTP 500 when a structurally valid page token contains an out-of-range timestamp. Protobuf 7.36.2 raises ValueError from Timestamp.FromNanoseconds(), while _after_cursor only converts OverflowError into InvalidParamsError.

Handle both exceptions so these tokens use the existing HTTP 400 / INVALID_ARGUMENT / Invalid page token response. The production change is one exception clause. Add four regression cases covering values immediately outside the timestamp range and very large positive/negative integers.

Verification

Tested source main at 2cc1dd5, Python 3.12.16, Windows, Protobuf 7.36.2, and SQLite/aiosqlite. Final checks used the exact dependencies exported from uv.lock with hash verification.

• Before the fix, all four new SQLite cases failed with ValueError; after the fix they pass. PostgreSQL/MySQL variants skip because their DSNs are unset.
• Exercised real Starlette REST routes, DefaultRequestHandlerV2, and an in-memory SQLite DatabaseTaskStore via httpx.ASGITransport, without mocking the conversion or store: three invalid timestamps changed from HTTP 500 to HTTP 400; ts=null and ts=0 remained HTTP 200. No provider requests.
• scripts/lint.sh: passed Ruff check/format and ty. ty reports three existing unused-ignore warnings in untouched client files; no type errors.
• The suite with the two Windows-incompatible integration modules below excluded: 2,556 passed, 215 skipped, 4 xfailed, 1 xpassed.
• The same suite with --cov=src --cov-report=term-missing --cov-fail-under=88: 93.57% coverage, same test counts.
• git diff --check: passed.

The passing suite command (with UTF-8 enabled for sample CLI subprocesses):

PYTHONUTF8=1 uv run pytest --timeout=45 -q \
  --ignore=tests/integration/cross_version/client_server/test_client_server.py \
  --ignore=tests/integration/push_notifications/test_default_push_notification_support.py

Full-suite limitations

I also ran the unfiltered suite; it was not green on this Windows host. Its initial result was 2,553 passed, 215 skipped, 4 xfailed, 1 xpassed, 3 failed, and 8 errors. The three sample CLI failures were GBK console-encoding errors and passed with PYTHONUTF8=1.

The two excluded modules fail on the unchanged production source too (verified by restoring the original exception clause and rerunning them): the cross-version harness uses POSIX os.killpg and :-joined PYTHONPATH and has short process startup/client timeouts; the push-notification harness cannot pickle a locally created FastAPI application under Windows spawn (FastAPI.setup.<locals>.openapi). I left these unrelated harnesses unchanged. Linux, PostgreSQL, and MySQL runs have not been performed locally.

Checklist

• Followed CONTRIBUTING.md and read the repository's AI workflow documents.
• Conventional Commit title and focused bug fix with regression coverage.
• Ran the lint script, unfiltered tests, and the passing suite/coverage commands described above.
• No documentation update needed: no public API or schema change.

AI disclosure: Codex investigated the code, reproduced the issue, prepared and reviewed this patch, and ran the checks under the account holder's instruction. Independent human review or reproduction is not claimed.