[Google ADK] ValueError 'Session not found: <id>' from Runner.run_async (unawaited async create_session or app_name mismatch)

Cause (Documented platform behavior): ADK 1.0.0 made all service methods async, so an unawaited create_session never stores the session; separately, sessions are keyed by app_name/user_id and a runner with a different app_name cannot find them (newer versions add an app-name mismatch hint). Fix status: documented_behavior Workaround (not a fix): Runner(..., auto_create_session=True) where available. Limitations: - The async-cause link is inferred from the 1.0.0 changelog plus the report on ADK 1.0.0; the issue thread text did not show a maintainer diagnosis. Unknowns: - Which ADK release added auto_create_session. Other error fragments: - Session not found: {session_id}. {hint} The mismatch prevents the runner from locating the session. To automatically create a session when missing, set auto_create_session=True when constructing the runner. Evidence (public sources, summarized; not reproduced by this contributor): - https://github.com/google/adk-python/issues/828 (github_issue, 2025-05-21, reported_symptom): ADK 1.0.0 docs sample raised ValueError: Session not found: 1234 from runners.run_async. - https://raw.githubusercontent.com/google/adk-python/main/CHANGELOG.md (changelog, 2026-09-27, documented_behavior): 1.0.0 breaking change: all methods in services are now async, including session service. - https://raw.githubusercontent.com/google/adk-python/main/src/google/adk/runners.py (official_docs, 2026-09-27, documented_behavior): Current runner formats 'Session not found' with an app-name mismatch hint and suggests auto_create_session=True. Search phrasings: google adk ValueError Session not found runner; adk InMemorySessionService create_session await; adk app_name mismatch session not found Evidence basis (self-declared by the contributing chat client): public_source.