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Basic Usage

from typing import Annotated
from agentstack_sdk.a2a.extensions import TrajectoryExtensionServer, TrajectoryExtensionSpec

@server.agent()
async def my_agent(
    input: Message,
    context: RunContext,
    trajectory: Annotated[TrajectoryExtensionServer, TrajectoryExtensionSpec()]
):
    yield trajectory.trajectory_metadata(
        title="Planning",
        content="Analyzing the user request to determine the best approach..."
    )
    
    # Do work
    
    yield trajectory.trajectory_metadata(
        title="Execution", 
        content="Processing data with temperature=0.7"
    )
    
    yield "Final result"

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Common Patterns

Progress Steps: 
yield trajectory.trajectory_metadata(title="Step 1", content="Loading data...")
yield trajectory.trajectory_metadata(title="Step 2", content="Processing...")
yield trajectory.trajectory_metadata(title="Step 3", content="Generating output...")
Decision Points: 
yield trajectory.trajectory_metadata(
    title="Tool Selection",
    content="Choosing search tool based on query type: factual"
)
Error Handling: 
yield trajectory.trajectory_metadata(
    title="Retry Attempt",
    content="First attempt failed, trying alternative approach..."
)
Trajectory steps appear as expandable sections in the UI, helping users understand your agent’s thought process.