Yemohyle/subagent telem

[yemohyleyemohyle]

Add persistent headerRequestId and parentToolCallId to the search and execute subagent telemetry for better tracking.

[Copilot]

Pull request overview

This PR improves telemetry correlation for search/execution subagent runs by (1) persisting a usable headerRequestId even when the service doesn’t echo x-request-id, and (2) propagating parentToolCallId so subagent model calls can be linked back to the parent agent tool invocation.

Changes:

• Add parentToolCallId to IChatRequestTelemetryProperties and include it in model-call telemetry events.
• Plumb parentToolCallId from tool invocation (chatStreamToolCallId) into the search/execution subagent request telemetry.
• Ensure headerRequestId is always populated by falling back to the client-generated request id when headers don’t include x-request-id.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/platform/networking/node/chatStream.ts	Includes parentToolCallId in per-model-call telemetry so subagent calls can be linked to the invoking tool call.
src/platform/networking/common/networking.ts	Extends request telemetry properties with parentToolCallId.
src/extension/tools/vscode-node/toolsService.ts	Broadens the span-context storage behavior to cover subagent tools beyond only runSubagent.
src/extension/tools/node/searchSubagentTool.ts	Passes the parent tool call id into the search subagent loop options.
src/extension/tools/node/executionSubagentTool.ts	Passes the parent tool call id into the execution subagent loop options.
src/extension/prompt/node/searchSubagentToolCallingLoop.ts	Adds requestId and parentToolCallId to subagent chat-request telemetry properties.
src/extension/prompt/node/executionSubagentToolCallingLoop.ts	Adds requestId and parentToolCallId to subagent chat-request telemetry properties.
src/extension/prompt/node/chatMLFetcher.ts	Persists headerRequestId by setting it up-front and falling back to the client request id when the response header is missing.