Capture host environment signals on MCP initialize

[edgarsskore]

Summary

Telemetry-only change, no behavior impact. Claude Code CLI, Claude Code inside the Claude Desktop app, and Cowork all report clientInfo.name = 'claude-code', so client_name alone cannot attribute initializes to the actual host.

Adds three raw, non-PII environment signals to the existing run_server_mcp_initialized event (no new event types):

Property	Source env var	CC CLI	CC in Desktop app	Cowork	Other clients
host_entrypoint	CLAUDE_CODE_ENTRYPOINT	cli	claude-desktop	—	—
host_agent	AI_AGENT	claude-code_<v>_harness	claude-code_<v>_harness	—	—
host_plugin_id	basename of CLAUDE_PLUGIN_DATA	plugin id or —	desktop-commander-inline	desktop-commander-inline	—

No client-specific branching in code — raw values are captured and segmentation happens in analytics:

CASE
  WHEN host_entrypoint = 'cli'            THEN 'claude-code-cli'
  WHEN host_entrypoint = 'claude-desktop' THEN 'claude-code-in-desktop-app'
  WHEN host_plugin_id  = 'desktop-commander-inline' THEN 'cowork'
  ELSE 'claude-code-other'
END

Testing

Verified end-to-end against production BigQuery telemetry with one controlled initialize per host (fresh client id each): all three contexts produced distinct signatures; non-Claude clients (e.g. codex-mcp-client) send no extra fields. Only the basename of CLAUDE_PLUGIN_DATA is captured — no user paths.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Improved initialization reporting by enriching the telemetry event with contextual environment details (entrypoint, agent, and plugin identifier) and truncating values for consistency.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: b9278b4c-b3ce-45c5-b0f1-e9a69980457e

📥 Commits

Reviewing files that changed from the base of the PR and between 0bdb8d8 and 14e2aa3.

📒 Files selected for processing (1)

• src/server.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• src/server.ts

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📝 Walkthrough

Walkthrough

src/server.ts now emits run_server_mcp_initialized telemetry with host_entrypoint, host_agent, and host_plugin_id derived from environment variables, and adds a path import to compute the plugin id.

Changes

Initialization Telemetry Enrichment

Layer / File(s)	Summary
Add path import and enrich telemetry event src/server.ts	Adds path import and updates the run_server_mcp_initialized capture call to include host_entrypoint, host_agent, and host_plugin_id derived from process.env.

Estimated code review effort: 1 (Trivial) | ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main telemetry change: capturing host environment signals during MCP initialization.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/initialize-host-signals

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