Tell real conversations from system-only threads (0.3.3)

[rameerez]

A system message is a message: post_system_message! bumps messages_count and moves last_message like a human one. The inbox relies on that, so "Your ride was cancelled" still surfaces a thread nobody typed in. Ops walls, moderation lists and analytics ask the opposite question: did a person actually say anything here? CarHey's madmin chats wall answered it with its own EXISTS subquery and a PostgreSQL-only DISTINCT ON "last human message" query. The primitive belongs in the gem.

Everything is additive. The inbox, unread counts, messages_count and last_message behave exactly as before.

• Chats::Message.conversational: kind text and not deleted. A captionless photo counts, a tombstone does not.
• Chats::Conversation.with_conversation / .without_conversation: one correlated EXISTS / NOT EXISTS, built through Arel from Message.conversational so the two definitions cannot drift. They compose with inbox_for, about and unread_by and never multiply rows.
• Conversation#last_conversational_message: the newest of those, or nil. It is a query, not the denormalized pointer.
• Chats::Message.last_conversational_in(conversations): the one-query batch twin for lists, ranked with ROW_NUMBER like Chats::Inbox's stacks. It returns a relation, so a host can narrow the columns before index_by(&:conversation_id). The ranked subquery is built unscoped so a chained .select never leaks into it.

README gains "Real conversations vs system-only threads" under the data model, plus the API reference lines and the Upgrading note. CHANGELOG has 0.3.3 - unreleased, and Chats::VERSION is 0.3.3. No gem was built or published.

Validation, run locally on Ruby 3.4.7:

Leg	Result
SQLite, Rails 8.1	340 runs, 1,400 assertions, 0 failures
SQLite, Rails 7.1	340 runs, 1,400 assertions, 0 failures
PostgreSQL 18	340 runs, 1,400 assertions, 0 failures
MySQL 8.4	340 runs, 1,400 assertions, 0 failures
RuboCop	82 files, no offenses

The new test/models/chats/conversational_scopes_test.rb has 15 tests. They cover text vs system vs tombstone vs empty threads in both directions, the exact-complement property, composition with inbox_for and unread_by, a single-query assertion for the scopes and the batch helper, and a created_at tie broken the way recent_first breaks it.

Host follow-up after the bump: CarHey's Madmin::ChatsDashboard swaps HUMAN_MESSAGE_SQL / real_conversations for with_conversation, and its human-message count and last-message queries for Message.conversational and last_conversational_in.

🤖 Generated with Claude Code

https://claude.ai/code/session_01T5EyMJjNWMPADZwjXBdiiZ