mattermore/DECISIONS.md

Design Decisions

This file records architectural choices and the alternatives considered. New entries are added when a design decision is resolved (not when options are brainstormed). Unresolved questions live in DESIGN.md §10.

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Why Mattermost Plugin vs Bot Account

Context: AI assistants in Mattermost can be implemented as plugins (running inside the Mattermost server process) or as bot accounts (independent services using the REST API and WebSocket).

Alternatives considered:

1. Plugin — hooks into slash commands, message hooks, KV store, System Console config UI, and the plugin lifecycle. No separate process to manage. Deployment is a single .tar.gz upload.
2. Bot account — separate service, more language freedom, but requires managing OAuth tokens, WebSocket reconnection, a separate process with its own lifecycle, and the bot account itself in Mattermost.

Outcome: Plugin chosen for v0.1.0 because:

• Single deployment artifact
• Built-in config UI via System Console
• No bot account to create and maintain
• KV store for persistence without a database
• Simpler for the target audience (self-hosted teams)

Trade-off: Plugin runs inside the Mattermost process — bugs can affect server stability. Mitigated by standard isolation practices (panic recovery, goroutine lifecycle management).

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Why Ollama

Context: Backend LLM provider for the plugin.

Alternatives considered:

1. Ollama — Single binary, simple REST API, streaming, model management, self-hosted (data never leaves the infrastructure). Community Edition friendly.
2. OpenAI / Anthropic API — SaaS, API key required, data leaves the network, ongoing API costs. Not aligned with self-hosted Mattermost ethos.
3. Local inference (llama.cpp, etc.) — More complex to set up and manage. Ollama wraps this with a clean API.

Outcome: Ollama. It matches the self-hosted, no-data-leaves paradigm of Mattermost Community Edition and provides the simplest API surface for a plugin to consume.

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Why Per-Channel Per-User Context (Proposed)

Context: When a user sends /ai <prompt>, should the plugin remember previous exchanges?

Alternatives considered:

1. Per-user global — Context follows the user across channels. Simple but confusing: context from a #general question leaks into #dev.
2. Per-channel per-user — Each user gets separate context in each channel. Natural mapping: different channels are different topics.
3. No context — Stateless. Simplest but every prompt is isolated; users can't have a conversation.

Outcome (proposed): Per-channel per-user. Marked as D2 in DESIGN.md — not final until v0.1.0 implementation.

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