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+# AGENTS.md - Coding Agent Instructions
+
+This document provides essential information for AI coding agents working in this repository.
+
+## Project Overview
+
+**Quartz** is a static site generator for publishing digital gardens and notes as websites.
+Built with TypeScript, Preact, and unified/remark/rehype for markdown processing.
+
+| Stack         | Technology                                |
+| ------------- | ----------------------------------------- |
+| Language      | TypeScript 5.x (strict mode)              |
+| Runtime       | Node.js >=22 (v22.16.0 pinned)            |
+| Package Mgr   | npm >=10.9.2                              |
+| Module System | ES Modules (`"type": "module"`)           |
+| UI Framework  | Preact 10.x (JSX with `react-jsx` pragma) |
+| Build Tool    | esbuild                                   |
+| Styling       | SCSS via esbuild-sass-plugin              |
+
+## Build, Lint, and Test Commands
+
+```bash
+# Type check and format check (CI validation)
+npm run check
+
+# Auto-format code with Prettier
+npm run format
+
+# Run all tests
+npm run test
+
+# Run a single test file
+npx tsx --test quartz/util/path.test.ts
+
+# Run tests matching a pattern (use --test-name-pattern)
+npx tsx --test --test-name-pattern="typeguards" quartz/util/path.test.ts
+
+# Build the static site
+npx quartz build
+
+# Build and serve with hot reload
+npx quartz build --serve
+
+# Profile build performance
+npm run profile
+```
+
+### Test Files Location
+
+Tests use Node.js native test runner via `tsx`. Test files follow the `*.test.ts` pattern:
+
+- `quartz/util/path.test.ts`
+- `quartz/util/fileTrie.test.ts`
+- `quartz/components/scripts/search.test.ts`
+
+## Code Style Guidelines
+
+### Prettier Configuration (`.prettierrc`)
+
+```json
+{
+  "printWidth": 100,
+  "tabWidth": 2,
+  "semi": false,
+  "trailingComma": "all",
+  "quoteProps": "as-needed"
+}
+```
+
+**No ESLint** - only Prettier for formatting. Run `npm run format` before committing.
+
+### TypeScript Configuration
+
+- **Strict mode enabled** (`strict: true`)
+- `noUnusedLocals: true` - no unused variables
+- `noUnusedParameters: true` - no unused function parameters
+- JSX configured for Preact (`jsxImportSource: "preact"`)
+
+### Import Conventions
+
+```typescript
+// 1. External packages first
+import { PluggableList } from "unified"
+import { visit } from "unist-util-visit"
+
+// 2. Internal utilities/types (relative paths)
+import { QuartzTransformerPlugin } from "../types"
+import { FilePath, slugifyFilePath } from "../../util/path"
+import { i18n } from "../../i18n"
+```
+
+### Naming Conventions
+
+| Element          | Convention   | Example                             |
+| ---------------- | ------------ | ----------------------------------- |
+| Files (utils)    | camelCase    | `path.ts`, `fileTrie.ts`            |
+| Files (comps)    | PascalCase   | `TableOfContents.tsx`, `Search.tsx` |
+| Types/Interfaces | PascalCase   | `QuartzComponent`, `FullSlug`       |
+| Type Guards      | `is*` prefix | `isFilePath()`, `isFullSlug()`      |
+| Constants        | UPPER_CASE   | `QUARTZ`, `UPSTREAM_NAME`           |
+| Options types    | `Options`    | `interface Options { ... }`         |
+
+### Branded Types Pattern
+
+This codebase uses branded types for type-safe path handling:
+
+```typescript
+type SlugLike<T> = string & { __brand: T }
+export type FilePath = SlugLike<"filepath">
+export type FullSlug = SlugLike<"full">
+export type SimpleSlug = SlugLike<"simple">
+
+// Always validate with type guards before using
+export function isFilePath(s: string): s is FilePath { ... }
+```
+
+### Component Pattern (Preact)
+
+Components use a factory function pattern with attached static properties:
+
+```typescript
+export default ((userOpts?: Partial<Options>) => {
+  const opts: Options = { ...defaultOptions, ...userOpts }
+
+  const ComponentName: QuartzComponent = ({ cfg, displayClass }: QuartzComponentProps) => {
+    return <div class={classNames(displayClass, "component-name")}>...</div>
+  }
+
+  ComponentName.css = style           // SCSS styles
+  ComponentName.afterDOMLoaded = script  // Client-side JS
+  return ComponentName
+}) satisfies QuartzComponentConstructor
+```
+
+### Plugin Pattern
+
+Three plugin types: transformers, filters, and emitters.
+
+```typescript
+export const PluginName: QuartzTransformerPlugin<Partial<Options>> = (userOpts) => {
+  const opts = { ...defaultOptions, ...userOpts }
+  return {
+    name: "PluginName",
+    markdownPlugins(ctx) { return [...] },
+    htmlPlugins(ctx) { return [...] },
+    externalResources(ctx) { return { js: [], css: [] } },
+  }
+}
+```
+
+### Testing Pattern
+
+Use Node.js native test runner with `assert`:
+
+```typescript
+import test, { describe, beforeEach } from "node:test"
+import assert from "node:assert"
+
+describe("FeatureName", () => {
+  test("should do something", () => {
+    assert.strictEqual(actual, expected)
+    assert.deepStrictEqual(actualObj, expectedObj)
+    assert(condition) // truthy assertion
+    assert(!condition) // falsy assertion
+  })
+})
+```
+
+### Error Handling
+
+- Use `try/catch` for critical operations (file I/O, parsing)
+- Custom `trace` utility for error reporting with stack traces
+- `process.exit(1)` for fatal errors
+- `console.warn()` for non-fatal issues
+
+### Async Patterns
+
+- Prefer `async/await` over raw promises
+- Use async generators (`async *emit()`) for streaming file output
+- Use `async-mutex` for concurrent build protection
+
+## Project Structure
+
+```
+quartz/
+├── bootstrap-cli.mjs    # CLI entry point
+├── build.ts             # Build orchestration
+├── cfg.ts               # Configuration types
+├── components/          # Preact UI components
+│   ├── *.tsx            # Components
+│   ├── scripts/         # Client-side scripts (*.inline.ts)
+│   └── styles/          # Component SCSS
+├── plugins/
+│   ├── transformers/    # Markdown AST transformers
+│   ├── filters/         # Content filters
+│   ├── emitters/        # Output generators
+│   └── types.ts         # Plugin type definitions
+├── processors/          # Build pipeline (parse/filter/emit)
+├── util/                # Utility functions
+└── i18n/                # Internationalization (30+ locales)
+```
+
+## Branch Workflow
+
+This is a fork of [jackyzha0/quartz](https://github.com/jackyzha0/quartz) with org-roam customizations.
+
+| Branch      | Purpose                                          |
+| ----------- | ------------------------------------------------ |
+| `main`      | Clean mirror of upstream quartz — no custom code |
+| `org-roam`  | Default branch — all customizations live here    |
+| `feature/*` | Short-lived branches off `org-roam`              |
+
+### Pulling Upstream Updates
+
+```bash
+git checkout main
+git fetch upstream
+git merge upstream/main
+git checkout org-roam
+git merge main
+# Resolve conflicts if any, then commit
+```
+
+### Working on Features
+
+```bash
+git checkout org-roam
+git checkout -b feature/my-feature
+# ... work ...
+git checkout org-roam
+git merge feature/my-feature
+git branch -d feature/my-feature
+```
+
+**Merge direction:** `upstream → main → org-roam → feature/*`
+
+## Important Notes
+
+- **Client-side scripts**: Use `.inline.ts` suffix, bundled via esbuild
+- **Isomorphic code**: `quartz/util/path.ts` must not use Node.js APIs
+- **Incremental builds**: Plugins can implement `partialEmit` for efficiency
+- **Markdown flavors**: Supports Obsidian (`ofm.ts`) and Roam (`roam.ts`) syntax