# ADR-003: SSR Strategy - Go Templates with Preact Hydration

## Status
Accepted

## Context
The application needs to serve document pages that are readable without JavaScript (for performance and accessibility), while providing rich interactivity (comments, editing, search) when JavaScript is available. We need a server-side rendering strategy that works with our Go backend and Preact frontend.

## Decision
**Strategy C**: Go's `html/template` renders initial HTML for all pages. Preact hydrates interactive components on the client.

### Implementation Details

1. **Server Rendering**:
   - Go handlers query database for document content
   - Markdown parsed to HTML server-side (Goldmark)
   - `html/template` renders full page with document HTML embedded
   - No JavaScript required for reading

2. **Client Hydration**:
   - Preact components mount into designated DOM containers
   - Comments, search, editor are Preact islands
   - Static content remains server-rendered HTML
   - `preact-iso` handles client-side navigation between pages

3. **Data Passing**:
   - Initial state embedded as JSON in `<script type="application/json">` tags
   - Preact reads initial state during hydration, avoids extra API calls
   - CSP nonce applied to all inline scripts

## Consequences

### Positive
- First contentful paint is instant (pure HTML)
- SEO-friendly without extra complexity
- Graceful degradation: works without JS
- Go templates are auto-escaping XSS-safe
- No V8/JS runtime embedded in Go binary
- Smaller client bundle (only interactive components)

### Negative
- Some code duplication: markdown parsing logic in both Go and JS (for preview)
- Template syntax is verbose compared to JSX
- Hydration can cause flicker if not carefully managed
- Client state must reconcile with server-rendered HTML

## Alternatives Considered

### Go Templates Only (No Preact)
- **Pros**: Zero client JS, maximum performance
- **Cons**: No interactive features (comments, real-time sync, search)
- **Rejected**: Doesn't meet collaboration requirements

### Embedded JS Runtime (QuickJS/V8)
- **Pros**: True isomorphic rendering, JSX templates
- **Cons**: Adds C dependency, complex build, larger binary, security surface area
- **Rejected**: Violates minimal dependency principle

### Preact SSR via WASM
- **Pros**: Same templates on server and client
- **Cons**: WASM overhead, complex build pipeline, slower than Go templates
- **Rejected**: Go templates are faster and simpler

## References
- Go html/template security: https://pkg.go.dev/html/template
- Preact hydration: https://preactjs.com/guide/v10/server-side-rendering
- Islands Architecture: https://jasonformat.com/islands-architecture/
