Compatibility Scope

This page is the canonical entry point for Mattermost compatibility expectations.

Compatibility Commitment

RustChat prioritizes compatibility with Mattermost mobile and desktop clients on /api/v4/* and /api/v4/websocket.

Current Headline Coverage

Scope	Coverage	Last Audited
Mobile-critical endpoints	41/41 implemented	2026-05-22

Previously tracked gaps now implemented:

• POST /api/v4/emoji
• POST /api/v4/posts/search

Known limitations:

• Post search is currently a basic message search implementation, not full Mattermost advanced search parity.
• Advanced post action endpoints that RustChat does not implement return explicit Mattermost-shaped 501 responses instead of success-shaped no-ops.
• Unread mention counting uses token-boundary matching for @user, @all, @channel, and @here; persisted mention-target storage and full Mattermost notification preference parity remain future work.
• Plugin, LDAP, SAML, compliance, and some enterprise/admin APIs remain compatibility stubs or intentionally scoped out.

Protected Compatibility Surface

Changes in these paths should be treated as compatibility-sensitive:

• backend/src/api/v4/
• backend/src/mattermost_compat/
• backend/compat/
• backend/src/realtime/

Verification Expectations

When compatibility-sensitive changes are made:

# Compatibility workflow
cd backend
cargo test --no-fail-fast -- --nocapture

Also review compatibility guidance in:

• Development Compatibility Guide
• Reference Compatibility Matrix