Paywall offer for mixer packs, shared packs, and the launch price stage (#705)

[Skeyelab]

#705, the Kit for slices 3 and 4: the offer model, shared packs, and the price stage. Stacked on #769. Auto-merge stays off until it's retargeted to main. Still no app change; the app PR wires this up behind PackAvailability.

Decisions it implements (Eric, through the coordinating session, 2026-10-16)

• Offer (PackOffer.items):
  • Pro owned: nothing.
  • Packs not offered in this build: Pro only.
  • A pack bought by this person: only .upgrade, since a second pack is hidden.
  • Only a Family Shared pack: .pro, which is option (a).
  • An Armed X Air or X32: .pack(family), then .pro.
  • Otherwise, including a generic input: .pro.
• Headline (PackOffer.headline): "Pro for your XR18", from the linked Mixer's model. Without a link it uses the family's name ("X Air", "X32").
• Availability: PackAvailability is Debug only. It doesn't reach TestFlight or the App Store until Eric tries packs on a device.
• Price stage: PriceStage.current = .launch, with the label "Launch price" at that stage only. The coordinating session set Pro to $4.99 in App Store Connect. Moving to the next stage is a one-line PR.

Shared versus bought (OwnedPurchase.isFamilyShared, ProPurchases.boughtPacks, saved for cold start)

• An upgrade this person bought counts as Pro only with a pack they bought. Buying a pack and the upgrade, then refunding the pack, can't lean on a relative's shared pack.
• An upgrade shared with them counts with any owned pack. The upgrade has Family Sharing on like Pro (Eric), so a family keeps the buyer's Pro.
• The app PR must: set isFamilyShared from transaction.ownershipType == .familyShared in ProStore.refreshOwned() (today it's always false), load the pack and upgrade products, and pass boughtPacks to PackOffer.items.

Tests, written first (PackOfferTests, ProPurchasesTests):

• Red first, then green:
  • the offer suite (compile: no PackOffer or PackAvailability);
  • sharedPackGetsPro, launchPrice and boughtVersusShared (compile);
  • boughtUpgradeNeedsBoughtPack (behavioral: the old rule let a shared pack carry it);
  • the headline trims a trailing newline (behavioral).
• Passed on their first run: sharedUpgradeWithSharedPack, because the old rule already allowed it; it now guards that case. Also the existing lastKnownPacks round-trip, which first went red when boughtPacks wasn't saved and was fixed by saving it.

Reviewed: a code-review agent found no blockers. Its "should the upgrade use bought packs?" question was settled by Eric's Family Sharing answer, as above. Its two nits (wording, newline trim) are done.

Checked: full package tests (1,031) pass, and VERIFY_QUICK=1 ./scripts/verify.sh passes.

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../ShowRecorderKit/Sources/Recording/PackOffer.swift	85.71%	3 Missing ⚠️

📢 Thoughts on this report? Let us know!