[DOCS] Monitoring usage docs missing `claude_code.at_mention` OpenTelemetry event

Documentation Type

Missing documentation (feature not documented)

Documentation Location

https://code.claude.com/docs/en/monitoring-usage

Section/Topic

"Events" section in the OpenTelemetry monitoring guide

Current Documentation

The docs currently say:

Claude Code exports the following events via OpenTelemetry logs/events (when OTEL_LOGS_EXPORTER is configured): Event Name: claude_code.user_prompt ... Event Name: claude_code.tool_result ... Event Name: claude_code.api_request ... Event Name: claude_code.api_error ... Event Name: claude_code.api_request_body ... Event Name: claude_code.api_response_body ... Event Name: claude_code.tool_decision ... Event Name: claude_code.permission_mode_changed ... Event Name: claude_code.auth ... Event Name: claude_code.mcp_server_connection ... Event Name: claude_code.internal_error ... Event Name: claude_code.plugin_installed ... Event Name: claude_code.skill_activated ... Event Name: claude_code.api_retries_exhausted ... Event Name: claude_code.hook_execution_start ... Event Name: claude_code.hook_execution_complete ... Event Name: claude_code.compaction

No documentation currently exists here for the claude_code.at_mention OpenTelemetry log event added in v2.1.122.

What's Wrong or Missing?

The monitoring guide presents itself as the reference for Claude Code OpenTelemetry log events, but it does not document the new claude_code.at_mention event for @-mention resolution.

That leaves observability users without:

A. The event name to filter on

There is no entry telling users that claude_code.at_mention exists.

B. The event schema

The page does not explain which attributes this event emits, so users cannot build dashboards, alerts, or audit queries around @-mention resolution.

C. Release-to-docs continuity

The feature was added in v2.1.122, but the OpenTelemetry reference page has not been updated to reflect it.

Suggested Improvement

Add a new event subsection in the "Events" section for claude_code.at_mention, following the same format used for other OpenTelemetry events:

Event Name: claude_code.at_mention

Document:

• when the event is emitted during @-mention resolution
• the attributes included on the event
• any redaction or OTEL_LOG_TOOL_DETAILS gating behavior, if applicable
• how this event relates to existing @-mention features for files, subagents, and MCP resources

If the event is only emitted for certain @-mention types or only after successful resolution, that scope should be stated explicitly.

Impact

Medium - Makes feature difficult to understand

Additional Context

Affected Pages:

| Page | Line(s) | Context |
|------|---------|---------|
| https://code.claude.com/docs/en/monitoring-usage | 475-810 | OpenTelemetry events reference lists documented log events but does not include claude_code.at_mention |

Total scope: 1 page affected

Relevant release context: v2.1.122 added claude_code.at_mention as an OpenTelemetry log event for @-mention resolution, so the monitoring reference should be updated to match.