Patterns from shipping a ?welcome=creator outreach modal: piggyback on the existing chat-popup session-suppression flag instead of new props, build UTM-tagged URLs only at link-construction time (GA4 auto-captures; CRM link tracking preserves params), and never let CRM re-syncs blank optional fields.
Shipped a query-param-triggered pitch modal (?welcome=creator) on a public calculator page for B2B2C creator outreach. Three reusable patterns:
1. Suppress competing popups via their existing session key, not new plumbing. The page already had a chat-FAB auto-popup (scroll/time/exit-intent triggers) that honored a sessionStorage dismissal flag checked at fire time (can_auto_open()). The new modal's onMount just sets that same key — the auto-popup goes dormant for the whole session with zero changes to the other component, and the FAB stays manually clickable. Audit the existing popup's gating conditions first; if it checks a flag at trigger time (not mount time), setting the flag from a sibling component that mounts in the same tick is race-free.
2. UTM tags need zero frontend code — but audit for server-side redirects first. GA4 captures utm_* client-side from the landing URL, and CRM link-tracking wrappers (e.g. Folk) preserve query params, so the only code that touches UTMs is the pipeline helper that constructs the outreach URL (urlencode([('welcome','creator'),('utm_source',...),...])). The one thing that breaks this silently: a server hook that 301-redirects tracking params to a clean URL for SEO. Check hooks before shipping; prefer canonical-tag-on-pathname over redirects when client-side attribution matters.
3. CRM upsert re-syncs must include optional fields only when non-empty. A per-record URL field (set only after an artifact is published) was added to a CRM custom-field sync. If the desired-fields dict always included the key, a re-sync from a record without the URL would blank a CRM-side value set earlier (same class of bug as reverting a manually-advanced Status). Rule: fields that are 'set once when known' get included in the upsert payload only when truthy; the diff against current CRM values then never produces a destructive write.
Also: post-signup redirect from such a modal should use the clean path (param stripped), or returning users get re-pitched by their own welcome modal.