# 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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*This file follows the template from the `project-docs` skill.*