# Wire DashboardConfig + Add Caching + Add Size Limits

## Goal

Activate the dead `DashboardConfig` module, add basic server-side caching to eliminate redundant disk I/O on every API request, and add input size limits to the review POST endpoint.

## Requirements

### R1. Wire DashboardConfig into the frontend

`dashboard/config.py` defines 5 settings but none are consumed by the server or client. `self.config` is loaded at `ui/app.py:323` and immediately abandoned.

**Fix**:
- Add `GET /api/config` endpoint returning `config.to_dict()`
- Add `PUT /api/config` endpoint accepting `body: dict` and calling `config.save()`
- On dashboard init (`dashboard.js:466`), fetch `/api/config` and apply:
  - `auto_refresh_interval` → set polling interval (default 2s)
  - `default_view` → switch to board/stats/timeline on load
  - `theme` → set CSS `data-theme` attribute
  - `show_timelines` → show/hide timeline elements
  - `column_width` → set CSS `--col-min-width` variable
- Remove hardcoded `setInterval(refreshData, 2000)` on line 462 and use config value

### R2. Add server-side caching for task scans

Currently every `/api/tasks`, `/api/task/{name}`, and `/api/review-summary` call does a full `discover_tasks()` — reading all artifact files from disk. At 2s polling, this is thousands of file reads per minute for ~84KB of data.

**Fix**:
- Add a module-level cache with TTL (e.g., 1 second or triggered by review writes)
- `/api/tasks` returns cached data within TTL window
- `/api/task/{name}` looks up task by name from cached list instead of re-scanning
- Writing a review (`/api/task/{name}/review` POST) invalidates the cache
- Cache stores the list of `Task` objects, not the serialized JSON

### R3. Add input size limits to review POST

`ui/app.py:250-263` reads `content_length` from the header and reads the full body with no bounds check. A malicious client can:
- Send `Content-Length: 999999999` and never send the body → blocks single-threaded server (DoS)
- Send a 10MB comment → writes 10MB to REVIEW.md (disk abuse)

**Fix**:
- Add `MAX_POST_BODY = 65536` (64KB) constant
- If `content_length > MAX_POST_BODY`, return 413 Payload Too Large
- If `content_length <= 0`, return 400 Bad Request
- Cap `comment` to 4096 characters before writing to disk

### R4. Add `/api/task/{name}` to use cache

`_serve_task()` at `ui/app.py:170-195` calls `discover_tasks()` to find one task. Use the cache from R2 for O(1) lookup.

## Acceptance Criteria

- [ ] `GET /api/config` returns current config as JSON
- [ ] `PUT /api/config` with `{"theme": "dark"}` persists to `dashboard-config.json`
- [ ] Dashboard JS reads config on init and applies theme, default_view, auto_refresh_interval
- [ ] Changing config via dashboard-config.json and restarting dashboard applies the settings
- [ ] `/api/tasks` within TTL returns cached data (no disk reads on second poll)
- [ ] Writing a review via POST invalidates cache; next `/api/tasks` re-reads from disk
- [ ] POST with `Content-Length: 1000000` returns 413
- [ ] POST with comment > 4096 chars truncates to 4096 before writing
- [ ] `test_config.py` tests still pass
- [ ] `test_app.py` tests still pass

## Non-Goals

- Not implementing persistent caching (disk/memcached) — in-memory TTL is sufficient
- Not adding authentication to config endpoints (config changes require local access by design)
- Not optimizing `discover_tasks()` itself — the cache removes the hot path