[jmgasper]

What was broken

The previous PM-6594 fix (PR #19) added default challenge forum watches and new-topic emails. QA found that forum opt-out did not update topic/announcement watch states, and individually unwatched topics could still receive forum notifications.

Root cause

Topic reads treated any TopicWatch row as watched and ignored the forum preference. Topic unwatch deleted the row, losing the opt-out required to override forum defaults. New challenge topics also automatically watched their author independently of the forum preference.

What was changed

• Resolve topic list/detail watch state from the explicit topic choice, falling back to the effective challenge forum preference.
• Persist challenge-topic opt-outs and exclude them from notification recipients, including members watching through the forum or an ancestor.
• Preserve individual topic watches across forum opt-out and individual opt-outs across forum re-watch. Announcements follow the same rules.
• Let newly created challenge topics inherit the author's forum preference. Preserve general forum author watches and unwatch behavior.
• Add the TopicWatch.watching column, regenerate Prisma exports, and update documentation. Existing watch rows are preserved as opt-ins because historical rows do not distinguish manual from automatic author watches.

Deploy migration 20261020000000_topic_watch_preferences before this API, then Platform UI PR #2527. The previous challenge-watch migration remains required. No dependency changes.

Any added/updated tests

• HTTP regressions for registrants and copilots: list/detail/email consistency through watch → unwatch → re-watch, individual opt-ins/opt-outs, announcements, newly authored topics while unwatched, and explicit topic re-watch.
• PostgreSQL tests for inherited/null versus explicit true/false projections, default preservation, and idempotent preference updates.
• Command and recipient filtering regressions, including a topic opt-out overriding forum and ancestor watches.

Validation after nvm use:

• pnpm lint and pnpm build: passed; changed service/test files also checked directly with ESLint.
• pnpm exec prisma migrate deploy: all six migrations passed on disposable local PostgreSQL.
• pnpm test --runInBand with PostgreSQL schema checks: 193 passed, eight optional public-forum database tests skipped.
• All database suites enabled: 200 passed, one failed. The public-import category-topic:99001 provenance failure also reproduces on unchanged origin/develop (seven passed, one failed). No unrelated importer changes were made.