Telemetry: capture middle-click CTA opens

[reakaleek]

Why

CTA click telemetry (cta_clicked) is emitted from a click listener on the CTA link. Per the DOM spec, middle-click ("open in new tab") fires auxclick, not click, so those engagements were silently going untracked — undercounting CTA click-through rate for anyone opening links in a background tab.

What

Bind the existing CTA activation handler to auxclick as well, gated to event.button === 1 so right-click (context menu) doesn't also count as an engagement. Left-click, Cmd/Ctrl+click, and keyboard activation are unaffected — they already fire click.

Test plan

• prettier, tsc --noEmit, and eslint all pass (verified via husky pre-commit hooks)
• Load a page with a right-gutter CTA, open DevTools Network filtered to /v1/o/l, middle-click the CTA → new tab opens and a cta_clicked log record is sent (previously nothing was sent)
• Left-click and Cmd/Ctrl+click still emit cta_clicked as before

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: f1125412-3c3d-4a28-af47-74fd501bee9a

📥 Commits

Reviewing files that changed from the base of the PR and between a636374 and 4f3cd42.

📒 Files selected for processing (1)

• src/Elastic.Documentation.Site/Assets/main.ts

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📝 Walkthrough

Walkthrough

The CTA click tracking logic in main.ts was refactored to extract the click handling into a named function, handleCtaActivation, which is now used for both the standard click listener and a new auxclick listener. The auxclick listener triggers the same handler only when the middle mouse button (button === 1) is used, enabling tracking of middle-click CTA activations that don't fire a standard click event.

Sequence Diagram(s)

sequenceDiagram
  participant User
  participant Document
  participant handleCtaActivation
  participant Telemetry

  User->>Document: click on a[data-cta]
  Document->>handleCtaActivation: click event
  handleCtaActivation->>Telemetry: emit cta_clicked

  User->>Document: middle-click on a[data-cta]
  Document->>handleCtaActivation: auxclick event (button===1)
  handleCtaActivation->>Telemetry: emit cta_clicked

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Estimated code review effort: Medium

Suggested labels: frontend, analytics

Suggested reviewers: none identified from available context

Poem
A rabbit clicks with middle paw,
No click event, but auxclick's law!
One handler now does double duty,
Tracking clicks with extra beauty. 🐰🖱️

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the main change: tracking middle-click CTA opens.
Description check	✅ Passed	The description is directly related to the telemetry change and its implementation details.
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

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch telemetry/cta-auxclick

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