docs(clay-ads): add audience size glossary entry and match rate vs audience size FAQ

[george-dilthey]

What changed

Applied three substantive deltas from the upstream Webflow update to docs/clay-ads.md:

1. Fixed Re-target → Retarget in the key use cases bullet list (spelling consistency).
2. Added a new Audience size glossary entry (upstream added this term to distinguish it from match rate).
3. Added a new FAQ "Why is my match rate high but my audience size much smaller?" explaining that match rate and audience size count different things — match rate is the share of contacts tied to platform users, while audience size is the subset currently serviceable (opted in, signed in, eligible for the inventory).

Why

Triggered by a Webflow collection_item_published webhook for https://university.clay.com/docs/clay-ads. The upstream page received multiple changes; this PR applies the deltas that have a clean home in the local doc. See "Uncertainties" for the two deltas that were not applied.

Source link(s)

• Upstream Webflow page: https://university.clay.com/docs/clay-ads
• Verifier sub-agent returned BETA (Growth/Enterprise gate) for all applied claims. The doc already states "Ad audiences are available on Growth and Enterprise plans" in the FAQ, so the plan-access framing is already present. No additional beta note needed for the new content.
• Code evidence:
  • matchRate and audienceSize are distinct fields: clay-base/libs/api-contract/src/ad-audiences/interfaces.ts:200,202
  • Both rendered as separate labeled stats: clay-base/apps/frontend/src/components/AdAudienceSidebar/components/ProviderCard.tsx:371,417
  • Google per-network split (Search/Display) confirmed: ProviderCard.tsx:391–397; populated at clay-base/apps/frontend/src/components/AdSyncs/AdSyncSyncStage/provider-sync-run-summary.ts:61–62
  • Plan gate: clay-base/apps/frontend/src/hooks/ad-syncs/useAdsEntitlement.ts:36

Uncertainties

• Hashing paragraph not applied: Upstream added a new paragraph in Step 5 (Enhanced matching) about platform-specific hashing rules ("Google Ads takes first and last name hashed with SHA-256 but country and postal code in the clear, for instance, while Meta Ads hashes its location fields too."). The verifier confirmed this is accurate (google-field-validators.ts and meta-field-validators.ts). However, the local doc has no "Step 5: Turn on Enhanced matching" section — the local doc is structured around the old table-based workflow. No clean structural home was found; this paragraph was not inserted to avoid restructuring unrelated parts of the doc. A reviewer familiar with the local doc structure should decide where this belongs.
• Match rate definition rewording not applied: Upstream updated the Match rate glossary definition to reference "identity graph." The local version is richer — it includes specific percentage benchmarks (40–60%+ on Meta, ~95% on LinkedIn) that are locally enriched and should not be discarded. Upstream definition was not applied; local version preserved.

Related observations

• The local doc's structure (table-based workflow) diverges significantly from the upstream (Audiences segment-based workflow). Several upstream sections (Steps 1–6, "Where you can sync" table, "What to expect after your first sync") have no equivalent in local. This divergence is pre-existing and not in scope for this PR.
• The upstream FAQ "Why did fewer contacts sync than my segment contains?" was expanded with a new paragraph about first-party vs. marketplace data rules. The local doc already has richer, differently-structured coverage of this topic in "Why are some contacts excluded when I set up an ad sync?" — not applied.

Closes DOC-2033

[linear-code]

DOC-2033