fix(analytics): record link-configured UTMs on click events (SIT-382)

[onamfc]

SIT-382

The problem

click_events.utm_* was only ever populated from the inbound query string on the short-link request. UTMs configured in link settings are appended to the destination URL by buildRedirectUrl, so they reached the landing page but never the click row. Every campaign analytics surface read NULL for a link-tagged click.

Verified against production: a pro-tier workspace had 0 of 3,111 clicks carrying a campaign, all-time, while 3,758 of its web events carried one.

The change

resolveClickUtms() resolves source / medium / campaign independently — inbound query-string value wins, link configuration fills anything left blank.

Inbound takes precedence because a value a sharer put on the short URL is more specific than static link configuration. Production has one workspace running Meta ads into a link whose configured campaign is the placeholder test; letting configuration win would replace their real per-ad campaign IDs with test.

Blank and whitespace-only values resolve to undefined rather than '', since campaign analytics filters on IS NOT NULL AND <> '' but groups on the raw value. Values are stored trimmed so " ig" and "ig" don't split into two UTM library entries. A repeated query parameter arriving as an array falls through to configuration instead of being handed to a VARCHAR column.

Blast radius

Strictly additive — no backfill, so no historical number changes. The write is inside setImmediate after the response, so redirect latency is untouched.

redirect.ts changes are two hunks (the import and the resolution block). Nothing within 90 lines of buildRedirectUrl (467, 606) or lf_click (629) — the destination URL and click-id paths are provably untouched.

Verification

• npx tsc --noEmit clean
• 213 tests pass across 14 files, including redirect.safety.test.ts
• npm run build clean
• 13 new cases in utils.test.ts covering precedence, per-key mixing, blanks, whitespace, non-object utm_parameters, and array query params

Note for whoever deploys

Campaign data will appear to start from zero on deploy day for workspaces that tag links. It's new data, not a spike — worth a changelog line so nobody trends across the discontinuity.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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