test(#265): broaden messaging conformance beyond C7–C14/1:1 (+ fix a .NET pagination bug)

[TortoiseWolfe]

What & why

The shared conformance suite (the anti-drift alarm across the Supabase↔.NET seam) covered only C7–C14 on a 1:1 conversation — the honest DoD from #265. This extends it (both providers run the identical cases) to close the biggest gaps, keeping the owner-blocking #280 arc moving.

New cases (12 → 19 per provider)

• C7 getMessageById — a participant reads the row; an outsider gets null.
• getProfiles — batch display-name/avatar lookup returns the requested users.
• markAsDelivered — a participant sets delivered_at; a non-participant outsider cannot.
• C7 pagination — newest-first, cursor + hasMore.
• C5 archive/unarchive — a per-participant view flag (the other participant's view is untouched).
• C1/C2 group scoping — a new group conversation + conversation_members in the harness; a member reads it, an outsider gets no metadata and no rows.

Full pnpm test:rls = 127/127 (both providers + the RLS suite + the #321 backstop).

Caught + fixed a real bug 🎯

The pagination case exposed a genuine .NET provider bug: DotnetMessagingProvider.getMessages returned the raw server JSON as MessagesPage, but the server serializes with the global snake_case policy, so the flag arrives as has_more — meaning hasMore was undefined. Pagination would silently break whenever the app runs on the .NET backend. Fixed the provider to map has_more → hasMore (the rows are already snake_case MessageRow, matching the wire). This is exactly the anti-drift catch the suite exists for — the existing tests never checked hasMore, so it was latent.

Harness (symmetric in both runners)

groupConversationId + group seeding (NULL participants per the check_group_participants constraint; membership via conversation_members), a conversationId param on seedMessage, delivered_at on readMessage, and a readConversation helper.

Still out of scope (honest)

• Realtime (C29) — the .NET realtime provider is a 5s polling fallback; a deterministic cross-provider assertion is timing-sensitive. Deferred (C29 is already indirectly covered by the outsider-sees-zero-rows check).
• C15–C28 — unallocated rule numbers (the interface defines only C1–C14 + C29). Materializing them is a design task (what rules?), not test-writing.

Self-validates: the diff touches tests/contract/** + src/services/messaging/**, both in the Conformance gate's path filter, so that gate runs the full test:rls against a fresh dual-provider stack.

Refs #265, #280.

🤖 Generated with Claude Code