fix(flags): A2A streaming

[saitarun-ent]

Description

The --stream flag was only working for HTTP agent runtimes and not A2A. This PR adds back the missing arguments needed to connect the flag to invokeA2ARuntime().

Related Issue

Closes #1887

Documentation PR

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

How have you tested the change?

• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[Copilot]

🟡 Not ready to approve

The new A2A streaming path has correctness gaps (notably text-part format handling and bearer-token streaming behavior) and lacks targeted unit test coverage for the new message/stream branch.

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Pull request overview

This PR fixes agentcore invoke --stream for A2A runtimes by plumbing the CLI --stream flag into the A2A invoke path and adding an A2A message/stream (SSE) implementation in the AgentCore client wrapper.

Changes:

• Passes the CLI --stream option through handleInvoke() into invokeA2ARuntime().
• Extends A2AInvokeOptions with a stream?: boolean flag.
• Implements an A2A message/stream SSE response reader to yield incremental text chunks.

File summaries

File	Description
src/cli/commands/invoke/action.ts	Wires --stream into the A2A invocation options passed to invokeA2ARuntime().
src/cli/aws/agentcore.ts	Adds an A2A streaming option and SSE parsing path for message/stream.

Review details

Suppressed comments (1)

src/cli/aws/agentcore.ts:1053

• Same as the status-update path: artifact-update streaming currently only recognizes kind:'text' parts, so streamed output can be silently empty if the runtime uses type:'text' parts (which is already supported in non-streaming parsing).

                  const text = artifact.parts
                    .filter(p => p.kind === 'text' && p.text)
                    .map(p => p.text!)
                    .join('');

• Files reviewed: 2/2 changed files
• Comments generated: 3
• Review effort level: Lite

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