# 09 — Settings

## 1. High-Level Overview

**Purpose**: User-scoped + system settings: language, theme, system params, directory paths, aircraft default (duplicated with Admin).

**Architectural Pattern**: Single-page feature, ~181 lines pre-consolidation.

**Upstream dependencies**: `00_foundation`, `01_api-transport`, `03_shared-ui`.

**Downstream consumers**: `10_app-shell` (routed at `/settings`).

## 2. Internal Interfaces

| Export | Notes |
|--------|-------|
| `SettingsPage()` | Top-level route component. Sub-sections: Personal (language, theme), System (params), Directories, Aircraft default. |

## 3. External API Specification

| Method | Path | Purpose |
|--------|------|---------|
| GET / PUT | `/api/annotations/settings/user` | Per-user UI preferences |
| GET / PUT | `/api/admin/settings/system` | System params (saveSystem) |
| GET / PUT | `/api/admin/settings/directories` | Storage paths (saveDirs) |
| GET / PUT | `/api/admin/settings/aircraft-default` | Aircraft default (duplicated with Admin) |

## 5. Implementation Details

**State Management**: Page-local React state per form section.

**Findings (B4, copied from state.json):**

1. **`saveSystem` / `saveDirs` lack `try/finally`** — PUT failure leaves `saving:true` permanently and the spinner never stops. Step 4.
2. **Numeric inputs use `parseInt(v) || 0`** — clearing a field silently writes 0. Step 4.
3. **No optimistic concurrency** (no version field, no ETag) — Step 6 problem-extraction.
4. **`handleToggleDefault` duplicated with AdminPage** — same global config behind two different pages. Surface intent in Step 6.
5. **Possibly should be guarded by a permission like `SETTINGS`** — spec doesn't have such a code; server-enforces via 403. Less clear-cut than the `/admin` gap. Surface in Step 6.

**Key Dependencies**: `react-i18next` (language switch).

## 7. Caveats & Edge Cases

- **Stuck-saving spinner** on PUT failure (#1).
- **Silent zero on cleared numeric input** (#2) — corrupts settings.
- **Aircraft default duplicated** with Admin — eventually one page should win.

## 8. Dependency Graph

**Must be implemented after**: `00_foundation`, `01_api-transport`, `03_shared-ui`.

**Can be implemented in parallel with**: every other feature page.

**Blocks**: `10_app-shell`.

## Module Inventory

| Path | Module Doc |
|------|------------|
| `src/features/settings/SettingsPage.tsx` | `_docs/02_document/modules/src__features__settings__SettingsPage.md` |