# AGENTS.md — Build guide for Mattermost Professional ## Project scope Run private team channels with threaded replies, unread tracking, search and a single reviewed incoming integration. Catalogue verdict: kinda. The core loop is buildable, but a dependable replacement becomes a real weekend or multi-day project. For Mattermost Professional, self-host team chat with channels, threads, search, and integrations. The hard boundary is managed operations, mobile push, enterprise security, support, and governance, plus network, moderation, and communication infrastructure. Use the implementation prompt below to define the deliverable. Complete each phase's acceptance checks before extending the scope. ## Working agreement - Inspect the repository and its existing instructions before choosing paths, dependencies or commands. Keep one coherent stack and explain changes to the proposed architecture. - Plan a vertical slice that accepts a real input and produces the useful output described below. Persist only the state the prompt calls for; respect memory-only and upstream-managed workflows. Use fixtures only when they are clearly labelled. - After scaffolding, document the actual install, development, check and build commands in README and keep them synchronized with the package or project manifest. Do not report commands as successful unless they ran. - Work in small steps. At handoff, list implemented flows, checks actually performed, remaining blockers, and any credentials or provider setup the owner must supply. - Do not publish, spend money, contact customers, delete source data or run irreversible migrations without the project owner's authorization. ## Prerequisites - Runtime and tools: TypeScript, React, Node and PostgreSQL with workspace membership enforced on the server. - Before starting: A PostgreSQL database, session authentication, two isolated example workspaces and private attachment storage. ## Stack and architecture - TypeScript, React, Node and PostgreSQL with workspace membership enforced on the server - Data design: Store Workspace, Membership, Channel, Message, ThreadRoot and ReadCursor; private channel membership gates history, files, search and event delivery. - Setup: A PostgreSQL database, session authentication, two isolated example workspaces and private attachment storage ## Security and data integrity - Check membership on reads, mutations, attachments and exports. Keep activity history separate from editable current state; do not make private records public through search. - Begin with one workspace and asynchronous delivery receipts. Enterprise identity, compliance retention, voice calls and federation are separate requirements; do not claim chat transport alone provides them. - Keep secrets outside client bundles and exported projects; document what leaves the device and make retention/deletion controls visible. ## Agent implementation rules - Project rule — domain: Store Workspace, Membership, Channel, Message, ThreadRoot and ReadCursor; private channel membership gates history, files, search and event delivery. - Project rule — scope and recovery: Begin with one workspace and asynchronous delivery receipts. Enterprise identity, compliance retention, voice calls and federation are separate requirements; do not claim chat transport alone provides them. - Project rule — acceptance: Remove a member from a private channel during a connected session; subsequent events and attachment reads are denied and search no longer reveals its messages. - Project rule — delivery: document real setup commands and permissions; do not claim a build, accuracy level, performance result or security certification that has not been demonstrated. ## Optional agent skills and references - Recommended skill: [supabase-postgres-best-practices](https://github.com/supabase/agent-skills/blob/main/skills/supabase-postgres-best-practices/SKILL.md) — review this PostgreSQL domain schema, uniqueness constraints, transaction boundaries and access-scoped queries; Supabase hosting is not required. Follow the maintainer's installation instructions and match its requirements to the chosen runtime. - Recommended skill: [web-design-guidelines](https://github.com/vercel-labs/agent-skills/blob/main/skills/web-design-guidelines/SKILL.md) — review keyboard access, focus, validation, error recovery and the readable work/review interface or HTML report. Follow the maintainer's installation instructions and match its requirements to the chosen runtime. Read the linked SKILL.md and its dependencies before adding a skill. Select only the skills matching this project's runtime and task; their documentation does not supply API access, credentials or approval to perform external actions. Pin the reviewed revision where the tool supports it. Follow the chosen agent's documented project-level installation mechanism. ## Distribution ideas These are optional planning notes. Obtain the owner's approval before publishing or contacting anyone. - Demonstrate this working slice using synthetic or explicitly authorized non-sensitive examples: Run private team channels with threaded replies, unread tracking, search and a single reviewed incoming integration. - Share a synthetic example export and the acceptance walkthrough; keep real customer, health, financial and source data private: Remove a member from a private channel during a connected session; subsequent events and attachment reads are denied and search no longer reveals its messages. - State the limits before asking someone to replace their existing tool: Begin with one workspace and asynchronous delivery receipts. Enterprise identity, compliance retention, voice calls and federation are separate requirements; do not claim chat transport alone provides them. ## Engineering roadmap 1. Phase 1 — Pin the working slice and create its example input: Run private team channels with threaded replies, unread tracking, search and a single reviewed incoming integration. Confirm setup: A PostgreSQL database, session authentication, two isolated example workspaces and private attachment storage. 2. Phase 2 — Implement persistence and write-time invariants before decorating the UI: Store Workspace, Membership, Channel, Message, ThreadRoot and ReadCursor; private channel membership gates history, files, search and event delivery. 3. Phase 3 — Connect the working view to real saved state. Check membership on reads, mutations, attachments and exports. Keep activity history separate from editable current state; do not make private records public through search. 4. Phase 4 — Expose the app-specific limits and recovery path in context: Begin with one workspace and asynchronous delivery receipts. Enterprise identity, compliance retention, voice calls and federation are separate requirements; do not claim chat transport alone provides them. 5. Phase 5 — Walk through this concrete acceptance case and preserve its exported evidence: Remove a member from a private channel during a connected session; subsequent events and attachment reads are denied and search no longer reveals its messages. Finish the README and backup/restore instructions; report unfinished capabilities explicitly. ## Paid-product capabilities outside this build - managed operations, mobile push, enterprise security, support, and governance - network effects - native mobile apps - video and voice infrastructure - enterprise moderation and discovery ## Implementation prompt Build the following focused alternative to Mattermost Professional. This is a deliberately limited personal or small-team substitute, not parity with the paid service. WORKING SLICE Run private team channels with threaded replies, unread tracking, search and a single reviewed incoming integration. SETUP AND ARCHITECTURE Use TypeScript, React, Node and PostgreSQL with workspace membership enforced on the server. Prerequisites: A PostgreSQL database, session authentication, two isolated example workspaces and private attachment storage. Before integrating anything, record actual versions and permissions, plus model files or provider limits only where used, in the README; make unavailable dependencies visible rather than simulating success. DOMAIN MODEL AND INVARIANTS Store Workspace, Membership, Channel, Message, ThreadRoot and ReadCursor; private channel membership gates history, files, search and event delivery. IMPLEMENTATION CONTRACT Check membership on reads, mutations, attachments and exports. Keep activity history separate from editable current state; do not make private records public through search. Provide an input/setup view, the main work view, and a review/export view appropriate to this workflow. Preserve the last saved state if a job or save fails. Include empty, loading, permission-denied, partial and retryable-error states. Log identifiers and error categories without secret values or unnecessary private content. APP-SPECIFIC BOUNDARY AND RECOVERY Begin with one workspace and asynchronous delivery receipts. Enterprise identity, compliance retention, voice calls and federation are separate requirements; do not claim chat transport alone provides them. ACCEPTANCE SCENARIO Remove a member from a private channel during a connected session; subsequent events and attachment reads are denied and search no longer reveals its messages. Also reopen the app after an interrupted operation, confirm the saved record/export remains inspectable, and document the recovery action. These are implementation acceptance requirements, not a claim that this guide has been tested. DELIVERY Deliver a runnable repository with migrations or project-format versioning, a non-sensitive example, environment/permission setup, the exact manual acceptance steps, and a backup/export-and-restore walkthrough. Implement the working slice before optional integrations; list any deferred paid-product capabilities honestly. Do not add capabilities outside the working slice just to resemble the original product. PROJECT RULES FOR AGENTS.md Keep the domain invariants above executable at the write boundary. Propose scope changes before adding providers or permissions. Never fabricate source evidence, publish results, identity matches or successful delivery. Preserve user originals and require an explicit confirmation for destructive changes or external publication. ## Completion evidence Demonstrate the prompt's acceptance scenarios against the scoped workflow. Include setup from a clean checkout and failure recovery. Check persistence across restart and export/restore only for the state the prompt says to store; for memory-only tools, confirm that temporary content is discarded as specified. Record actual results and remaining limitations. A detailed plan alone does not establish a working replacement.