Document source label on gateway_function_invocation_inflight

[welteki]

Description

Documents the new source label on gateway_function_invocation_inflight,
adds its values (queue-worker, unknown) and a migration note for the
increased cardinality, notes why gateway and queue-worker inflight counts can
differ, and corrects the previously mistyped started/inflight metric names.

Motivation and Context

The gateway gained a source label on the inflight invocation metric that was
not yet documented.

• I have raised an issue to propose this change (required)

How Has This Been Tested?

Ran the docs site locally with Docker and inspected the rendered page and links.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s

[reviewfn]

AI Pull Request Overview

Disclaimer: This review was generated by automated AI and may contain errors. Do not trust its outputs without human verification.

Summary

• Documentation-only PR scoped to docs/architecture/metrics.md.
• Corrects the documented gateway started and inflight metric names.
• Adds the source label to gateway_function_invocation_inflight and documents current values.
• Includes a migration note for the new label cardinality and a PromQL aggregation example.
• Explains why gateway and queue-worker inflight metrics may not match exactly.
• No blocking findings were identified in the scoped diff.

Approval rating (1-10)

9/10. The change is clear, scoped, and publishable; no blocking issues were found in the reviewed documentation diff.

Summary per file

Summary per file

File path	Summary
docs/architecture/metrics.md	Documents gateway inflight source label, migration impact, and related metric corrections.

Overall Assessment

The PR is ready from a review perspective. The added documentation is appropriately placed near the gateway metrics table, the internal anchors resolve to existing sections, and the migration note gives users a concrete PromQL pattern to preserve pre-upgrade behaviour.

Detailed Review

Detailed Review

Content review

No blocking findings.

• The title and scope of the page still fit the change: the new subsection expands the gateway metrics reference without changing the page's structure or audience.
• The opening sentence for the source label explains user value before listing values, which makes the new label useful for readers configuring dashboards or custom autoscaling rules.
• The migration note is actionable because it names the affected gateway version, describes the cardinality change, and provides a concrete sum by (function_name) query.
• The note comparing gateway and queue-worker inflight counts prevents a likely operator confusion and links to the local JetStream section where the queue-worker metric is listed.

AI agent details.

Agent processing time: 2m52.857s
Environment preparation time: 38.921s
Total time from webhook: 3m56.925s