Changed example to use the Global Instruction Plugin (#1244)

[JuanCaCoder]

Changed the code sample to use the GlobalInstructionPlugin.

[JuanCaCoder]

📝 Executive Summary

• Migrates the Python A2A Consuming Quickstart sample from the deprecated Agent.global_instruction parameter to GlobalInstructionPlugin registered via App(plugins=[...]).
• Aligns the quickstart with the modern ADK application architecture and prevents runtime DeprecationWarning exceptions while preserving global instruction behavior across sub-agents.
• Target doc: docs/a2a/quickstart-consuming.md (rendered under /a2a/quickstart-consuming/).

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🗂️ PR Consolidation & Verification Mapping

PR / Source Reference	Original Section	New Section	Change Description	Codebase Verification
docs/a2a/quickstart-consuming.md	#### How it works (Snippet)	#### How it works (Snippet)	Removed deprecated global_instruction from root_agent = Agent(...); added App(name="a2a_basic", root_agent=root_agent, plugins=[GlobalInstructionPlugin(...)]).	✅ PASS google/adk/plugins/global_instruction_plugin.py:L58-L85 google/adk/apps/app.py:L53-L83
docs/a2a/quickstart-consuming.md	#### How it works (Prose)	#### How it works (Admonition)	Added !!! note "Global instructions via Plugins" note explaining deprecation of Agent.global_instruction and pointing to GlobalInstructionPlugin.	✅ PASS google/adk/agents/llm_agent.py:L758-L766 docs/agents/llm-agents.md:L206-L210
docs/a2a/quickstart-consuming.md	Introductory text	Introductory text	Added link to GlobalInstructionPlugin under /plugins/#prebuilt-plugins.	✅ PASS docs/plugins/index.md:L67-L68

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🔍 Technical Verification Report

1. GlobalInstructionPlugin Implementation & Lifecycle:

   • Source: src/google/adk/plugins/global_instruction_plugin.py:L58-L115
   • Verified: GlobalInstructionPlugin inherits from BasePlugin. Its constructor accepts global_instruction: Union[str, InstructionProvider] = "" and name: str = "global_instruction". In before_model_callback, it resolves static strings or InstructionProvider callables and prepends the instruction to llm_request.config.system_instruction.

2. Agent.global_instruction Deprecation:

   • Source: src/google/adk/agents/llm_agent.py:L288-L299, L758-L766
   • Verified: The field is marked deprecated in docstrings and emits a runtime DeprecationWarning ("global_instruction field is deprecated and will be removed in a future version. Use GlobalInstructionPlugin instead for the same functionality at the App level.").

3. App Container Architecture:

   • Source: src/google/adk/apps/app.py:L53-L83
   • Verified: App requires name: str and root_agent: Union[BaseAgent, Any, None]. It accepts plugins: list[BasePlugin] = Field(default_factory=list), which applies registered plugins application-wide across all local and remote sub-agents.

4. Runner plugins Deprecation:

   • Source: src/google/adk/runners.py:L285-L286, L386-L387
   • Verified: Passing plugins directly to Runner is deprecated in favor of App(plugins=[...]), confirming App as the canonical entry point for plugin registration.

[JuanCaCoder]

📝 Executive Summary

• Updates the A2A Consuming Quickstart sample to replace the deprecated Agent.global_instruction parameter with the modular GlobalInstructionPlugin registered at the App level.
• Aligns the guide with ADK's modern architecture, ensuring application-wide instructions and personality persist across hierarchical sub-agents without runtime deprecation warnings.
• Targets: Target Doc: docs/a2a/quickstart-consuming.md

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🗂️ PR Consolidation & Verification Mapping

PR / Source Reference	Original Section	New / Updated Section	Change Description	Codebase Verification & GitHub Source
PR #2177 / Branch	docs/a2a/quickstart-consuming.md	docs/a2a/quickstart-consuming.md	Deprecate Agent(global_instruction=...) and adopt App(plugins=[GlobalInstructionPlugin(...)])	✅ PASS – global_instruction_plugin.py:L58-L124

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🔍 Technical Verification Report

1. GlobalInstructionPlugin Plugin Architecture:

   • Claimed Doc Behavior: Replaces the deprecated global_instruction field on Agent by providing system instruction injection across the agent hierarchy via GlobalInstructionPlugin registered on App.
   • Verified Code Implementation: GlobalInstructionPlugin extends BasePlugin and hooks into before_model_callback to prepend the global instruction to llm_request.config.system_instruction.
   • GitHub Source Link: src/google/adk/plugins/global_instruction_plugin.py#L58-L124
   • Status: ✅ PASS

2. Agent.global_instruction Deprecation Status:

   • Claimed Doc Behavior: States that the global_instruction parameter on Agent is deprecated in favor of GlobalInstructionPlugin.
   • Verified Code Implementation: LlmAgent.global_instruction is explicitly marked deprecated in docstrings and triggers a DeprecationWarning in _get_global_instruction.
   • GitHub Source Link: src/google/adk/agents/llm_agent.py#L288-L299, src/google/adk/agents/llm_agent.py#L758-L767
   • Status: ✅ PASS

3. App Container Initialization & Plugin Support:

   • Claimed Doc Behavior: Encapsulates root_agent and plugins inside an App(name="a2a_basic", root_agent=root_agent, plugins=[...]) definition.
   • Verified Code Implementation: App defines fields name: str, root_agent: Union[BaseAgent, Any, None], and plugins: list[BasePlugin] = Field(default_factory=list).
   • GitHub Source Link: src/google/adk/apps/app.py#L53-L83
   • Status: ✅ PASS

4. Module Imports Verification:

   • Claimed Doc Behavior:
     • from google.adk.apps import App
     • from google.adk.plugins.global_instruction_plugin import GlobalInstructionPlugin
     • from google.adk.agents.llm_agent import Agent
   • Verified Code Implementation:
     • App is exported in google.adk.apps.__all__.
     • GlobalInstructionPlugin is defined in google.adk.plugins.global_instruction_plugin.
     • Agent is defined as TypeAlias = LlmAgent in google.adk.agents.llm_agent.
   • GitHub Source Link: src/google/adk/apps/__init__.py#L20-L27, src/google/adk/plugins/global_instruction_plugin.py#L58-L74, src/google/adk/agents/llm_agent.py#L1322
   • Status: ✅ PASS

5. Internal Anchor Reference:

   • Claimed Doc Behavior: Links to [GlobalInstructionPlugin](/plugins/#prebuilt-plugins).
   • Verified Code Implementation: Section ## Prebuilt Plugins exists in docs/plugins/index.md and indexes GlobalInstructionPlugin.
   • GitHub Source Link: docs/plugins/index.md#L56-L73
   • Status: ✅ PASS