chore(release/candidate): release 2.1.0

[Jacksunwei]

🤖 I have created a release beep boop

2.1.0 (2026-05-23)

Features

• Add chart generation and artifact loading to data agent (db06416)
• Add support for creating sandboxes from templates and snapshots (cbd14eb)
• Add user.id to gen_ai.user.message log records for telemetry (eb379be)
• Fix error message telemetry for tool calls (e56c021)
• Preserve transcription event order in conversation trajectory (b3d0759)

Bug Fixes

• ci: Add python-dateutil dependency to stale-bot workflow (84fa984)
• ci: Prevent workflow failures in relocated adk_team samples (55cbc8c)
• ci: Use absolute path for PYTHONPATH in upload docs workflow (85223e6)
• cli: Fix --reload_agents for web (1307f8e)
• cli: Inform user to install optional dependency on missing google.cloud (57d677c)
• convert Union[Pydantic, Pydantic] tool args at runtime (104edc8), closes #5799
• Fix bug where grounding metadata in Gemini 3.1 live was being silently discarded (b9751eb)
• fix input and output transcription finished events for Gemini v3.1 (d17a2a3)
• lazy-import GCS evaluation managers in evals utility (5f91a9d)
• Make google-cloud-storage import lazy in skill utils (416775d)
• resolve circular import caused by llm_request (7e38fc8)
• Resolve circular import in base_tool (92cf192)
• tests: Append trailing newline to JSON test outputs (3329ced)
• tools: Prevent session drop on MCP tool error (933653c)
• update EditFileTool to handle cross-platform line breaks and escape regex characters (1f24553)

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