integrate-arcjet-guard-google-adk-py

# Integrate Arcjet Guard into Python Google ADK `arcjet.guard.google_adk` wraps the agent's existing Arcjet client. It never talks to the Arcjet API itself. Shared Guard fundamentals (client, rules, labels, decisions, capture, registration) live in [../arcjet/references/guards_python.md](../arcjet/references/guards_python.md). Load that reference for anything that is not Google ADK-specific. Official Python `google-adk>=2.0.0,<3` only — not JS `@google/adk` (`@arcjet/guard/google-adk/v2`, docs https://docs.arcjet.com/guards/google-adk/), not `@google/genai`, not Go / Java ADK. Importing `arcjet.guard.google_adk` does not load LangChain, CrewAI, or the JS adapter. The extra is safe (no chromadb). Exports: `guard_tool`, `guard_plugin`, `google_adk_context`. There is no inbound helper and no approval helper. Three surfaces, one decision rule: - **An authored `LlmAgent`** → `guard_tool`. Assign the returned callback to `LlmAgent(before_tool_callback=...)`. This is not a wrap around `FunctionTool`. - **Runner-wide / tools you did not attach a callback to** → `guard_plugin`. A Runner `BasePlugin` whose `before_tool_callback` is the run-wide gate. Put it **first**. - **Correlation** → `google_adk_context` reads a caller-owned id. It never mints. It never reads `invocation_id`. It never reads `trace_id`. It never reads session-service auto-ids. DENY is a skip dict with `arcjetDenied: true` (`ArcjetDenialResult`, camelCase keys). ADK treats any mapping — including `{...