Copilot telemetry hook write replaces all of ~/.copilot/hooks/aspire-telemetry.json #22218

Is there an existing issue for this?

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Describe the bug

CopilotAgentClient.ConfigureTelemetryHookAsync builds a new JSON object and writes it over the whole ~/.copilot/hooks/aspire-telemetry.json file. Any entries a user adds to that file by hand are lost each time aspire agent init runs, including a global refresh where no agents are selected. This whole-file write has been on main since #18009 and moved into CopilotAgentClient in #20946.

The file is named for Aspire and owned by it, and Copilot reads every file in ~/.copilot/hooks, so users can keep their own hooks in other files. Even so, merging into existing content (as the Claude settings.json path already does) would be safer.

Raised in review on #22078: #22078 (comment)

Expected Behavior

Running aspire agent init updates only the Aspire-managed hook entries in aspire-telemetry.json and preserves any other content in the file.

Steps To Reproduce

1. Run aspire agent init and configure Copilot so ~/.copilot/hooks/aspire-telemetry.json is created.
2. Add a custom hook entry to that file by hand.
3. Run aspire agent init again.
4. The custom entry is gone.

Exceptions (if any)

N/A

Aspire doctor output

N/A

Anything else?

Relevant code: src/Aspire.Cli/Agents/Copilot/CopilotAgentClient.cs (ConfigureTelemetryHookAsync).