feat: ~/.config/writ/config.toml for theme (presets/custom/overrides) and font (family+size), threaded into the app

Author: wilfreddenton

Cargo.lock

@@ -48,7 +48,7 @@ math = ["dep:ratex-parser", "dep:ratex-layout", "dep:ratex-render", "dep:ratex-t
 editor = ["git", "github", "watch"]
 
 # the desktop editor application (winit shell). implies editor.
-app = ["editor", "remote-images", "mermaid", "math", "dep:winit", "dep:arboard", "dep:open", "dep:clap"]
+app = ["editor", "remote-images", "mermaid", "math", "dep:winit", "dep:arboard", "dep:open", "dep:clap", "dep:toml", "dep:dirs"]
 
 # the GhostText daemon (writd binary)
 ghosttext = ["app", "dep:tokio-tungstenite", "dep:futures"]
@@ -88,6 +88,8 @@ rustls = { version = "0.23.36", features = ["ring"], optional = true }
 unicode-segmentation = "1.13"
 serde = { version = "1", features = ["derive"] }
 serde_json = { version = "1", optional = true }
+toml = { version = "0.8", optional = true }
+dirs = { version = "5", optional = true }
 tokio = { version = "1", features = ["full"], optional = true }
 tokio-tungstenite = { version = "0.29", optional = true }
 tree-sitter = "0.26"

Cargo.toml

@@ -29,9 +29,30 @@ Flags:
 | `--autosave` | Save on every edit (used by the GhostText daemon) |
 | `--github-repo <owner/repo>` | GitHub context for ref validation (else auto-detected from the git remote) |
 | `--github-token <token>` | GitHub API token (or the `GITHUB_TOKEN` env var) for ref validation, hover cards, and autocomplete |
+| `--config <path>` | Config file location (default `~/.config/writ/config.toml`) |
 
 writ is rendered on [winit](https://github.com/rust-windowing/winit) + [wgpu](https://wgpu.rs) + [Vello](https://github.com/linebender/vello) + [Parley](https://github.com/linebender/parley) (GPU 2D rendering and text layout). On Linux/Mesa (including Asahi) select the Vulkan backend with `WGPU_BACKEND=vulkan`. Fonts are resolved via [Fontique](https://github.com/linebender/parley) with fontconfig loaded at runtime — no `-dev` headers needed.
 
+### Configuration
+
+writ reads an optional TOML config from `~/.config/writ/config.toml` (platform config dir, overridable with `--config <path>`). It sets the theme and the document font; a missing or malformed file just falls back to the built-in defaults. See [`config.example.toml`](config.example.toml) for a fully commented example.
+
+```toml
+[font]
+family = "JetBrains Mono"   # must be monospace; verified at startup, falls back if not
+size = 18.0
+
+[theme]
+name = "nord"               # built-in: dracula (default), nord, solarized-light — or a [themes.*] you define
+
+[theme.overrides]           # optional per-color hex tweaks on top of the selected theme
+comment = "#7A88B8"
+```
+
+- **Themes.** Pick a built-in preset by `name`, or define your own under `[themes.<name>]` (any omitted color is inherited from dracula) and select it. `[theme.overrides]` applies hex tweaks on top. The 12 color slots are `background`, `surface`, `foreground`, `selection`, `comment`, `red`, `orange`, `yellow`, `green`, `cyan`, `purple`, `pink`.
+- **Font.** The family **must be monospace** — writ verifies fixed-pitch at startup and falls back to the system monospace (with a warning) if the font is proportional or not installed, protecting its deterministic wrapping.
+- Config is read once at startup; edits take effect on the next launch.
+
 ### Inline git diff
 
 When the open file lives in a git repository, writ renders a live inline diff against `HEAD`: added lines and words are tinted green, deleted lines appear as red "ghost" rows above their position, all with the same markdown rendering as the rest of the document. writ watches the file, so edits made by an external tool (e.g. an AI agent) reload and re-diff live.