Fix event type names for assistant messages

[moeyui1]

Fix event type names for assistant messages per https://github.com/github/copilot-sdk/blob/main/nodejs/src/generated/session-events.ts

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• I have read and followed the Guidance for submissions involving paid services.
• My contribution adds a new instruction, prompt, agent, skill, or workflow file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, agent, skill, or workflow with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.
• I am targeting the staged branch for this pull request.

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Description

Fix the event type names for assistant messages according to the actual definition in SDK: https://github.com/github/copilot-sdk/blob/main/nodejs/src/generated/session-events.ts

Type of Contribution

• New instruction file.
• New prompt file.
• New agent file.
• New plugin.
• New skill file.
• New agentic workflow.
• Update to existing instruction, prompt, agent, plugin, skill, or workflow.
• Other (please specify):

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Additional Notes

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By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[Copilot]

Pull request overview

Updates the Node.js Copilot SDK instruction examples to use the correct session event type names for streaming assistant message/reasoning deltas, aligning the docs with the SDK’s generated event definitions.

Changes:

• Replace assistant.message.delta with assistant.message_delta in streaming switch-case example.
• Replace assistant.reasoning.delta with assistant.reasoning_delta in streaming switch-case example.
• Update the “Streaming with Progress” example to check for assistant.message_delta instead of assistant.message.delta.