# Naming Conventions

> Version: 1.1
> Last Updated: 2026-06
> **This document is the authoritative source. `CLAUDE.md` only links here.**

This document defines naming rules for files, directories, and identifiers across the Cherry Studio monorepo. It encodes both industry consensus (React/TypeScript, Node.js, shadcn/Next.js) and project-specific conventions.

---

## Table of Contents

1. [Quick Reference](#1-quick-reference)
2. [Core Principles](#2-core-principles)
3. [File Naming](#3-file-naming)
4. [Directory Naming](#4-directory-naming)
5. [Identifier Naming](#5-identifier-naming)
6. [Edge Cases](#6-edge-cases)
7. [Decision Tree](#7-decision-tree)
8. [Appendix: References](#appendix-references)

---

## 1. Quick Reference

The 90% case. See later sections for full rules and edge cases.

| What you're naming | Convention | Example |
|---|---|---|
| Business React component file | `PascalCase.tsx` | `Sidebar.tsx` |
| `packages/ui/` shadcn component file | `kebab-case.tsx` | `button.tsx`, `input-group.tsx` |
| Hook file | `useXxx.ts` (camelCase, `use` prefix) | `useChatContext.ts` |
| Util / function file (function-as-default-export) | `camelCase.ts` | `markdownConverter.ts` |
| Class-as-default-export file | `PascalCase.ts` (matches class name) | `KnowledgeService.ts`, `IpcChannel.ts` |
| Test file | `*.test.ts(x)` | `mcp.test.ts` |
| Config file | `*.config.ts` | `vitest.config.ts` |
| Type declaration | `*.d.ts` (lowercase / kebab) | `env.d.ts` |
| Top-level meta doc | `UPPERCASE.md` | `README.md`, `CLAUDE.md` |
| Regular doc | `kebab-case.md` | `database-testing.md` |
| npm package directory (`packages/*`) | `kebab-case` | `ai-sdk-provider/` |
| Business React component directory | `PascalCase` | `CodeEditor/` |
| Bucket directory (categorical container) | lowercase **plural** noun | `services/`, `utils/`, `hooks/` |
| Business / domain module directory | `camelCase` | `apiServer/`, `fileProcessing/` |
| Feature module directory (large, multi-file domain) | `features/<camelCase>/` | `features/apiGateway/` |
| `packages/ui/` directory | `kebab-case` | `primitives/`, `button-group/` |
| TanStack route file under `src/renderer/routes/` | `kebab-case.tsx` | `api-server.tsx`, `quick-assistant.tsx` |

> Stateful singleton capabilities use only `Service` (default) or `Manager` (instance pool); multi-instance helper classes take no suffix — see §5.2. Files placed inside any `utils/` directory drop the `Utils` suffix — the directory already declares the role; see §3.2.

---

## 2. Core Principles

Three rules trump any specific table below when in conflict:

1. **Consistency beats style choice.** A directory that consistently uses a "suboptimal" convention is healthier than one mixing two "correct" conventions.
2. **Cross-platform case safety.** Never rely on case to distinguish two files (e.g. `Foo.ts` and `foo.ts` in the same directory). macOS/Windows are case-insensitive by default; Linux is case-sensitive. Mixing breaks CI.
3. **Toolchain constraints win.** npm package names, shadcn CLI conventions, and Next.js routing rules are hard requirements — they override stylistic preference.

---

## 3. File Naming

### 3.1 React Component Files (`.tsx`)

| Location | Convention | Rationale |
|---|---|---|
| `src/renderer/components/**` | `PascalCase.tsx` | Filename mirrors the exported component name. |
| `src/renderer/pages/**` | `PascalCase.tsx` | Filename mirrors the exported component name. |
| `packages/ui/**` (shadcn-derived) | `kebab-case.tsx` | Required by shadcn CLI for cross-OS file resolution. |

The component's **exported identifier** is always `PascalCase`, regardless of filename style:

```tsx
// packages/ui/src/components/primitives/button.tsx
export function Button() { /* ... */ }

// src/renderer/components/Sidebar.tsx
export function Sidebar() { /* ... */ }
```

### 3.2 TypeScript Source Files (`.ts`)

Choose based on **what the file's default / primary export is**:

| Primary export | Convention | Example |
|---|---|---|
| Hook function (`useXxx`) | `camelCase.ts`, must start with `use` | `useShortcuts.ts` |
| Plain function or function group | `camelCase.ts` | `markdownConverter.ts`, `fileOperations.ts` |
| Class (especially services) | `PascalCase.ts` (matches class name) | `KnowledgeService.ts`, `IpcChannel.ts`, `WindowManager.ts` |
| Constants / enums only | `camelCase.ts` | `errorCodes.ts` |
| Re-export barrel | `index.ts` | — |

**Note:** Files under `packages/ui/` use `kebab-case.ts` regardless of export type (e.g. `use-dnd-reorder.ts`, `reorder-visible-subset.ts`), per §4.6 — that scope-specific rule overrides this section. The exported identifier (e.g. `useDndReorder`) remains `camelCase`.

**Inside any `utils/` directory** — the directory declares the role, so the filename does not repeat it:

```
utils/assistant.ts   ✅
utils/model.ts       ✅
utils/notesTree.ts   ✅
```

A `*Utils` suffix is used only when the file lives outside any `utils/` directory.

**Hooks (`useXxx.ts`)** — live in `src/renderer/hooks/` (default, may group into sub-folders by feature) or co-located with the consuming feature.

**Renderer wrappers around `window.api.*`** — the renderer does not use `*Api`, `*Client`, or any other IPC-wrapper suffix. Categorize wrappers by module shape per §5.2.

**Leading-underscore files (`_xxx.ts`)** — inside a resource-file directory (one file per resource/domain, e.g. `db/schemas/`, `api/schemas/`), a `_`-prefixed file is a **cross-resource shared construct, not a private file**. It holds helpers reused across sibling resource files and is deliberately deep-imported by both siblings and external consumers. Examples: `db/schemas/_columnHelpers.ts`, `api/schemas/_endpointHelpers.ts`. The `_` marks "not itself a resource," never "internal — do not import."

### 3.3 Test Files

- **Suffix**: `*.test.ts` or `*.test.tsx`. Do **not** use `.spec.*`.
- **Location**: prefer co-location in `__tests__/` subdirectory next to source. Inline (`foo.ts` + `foo.test.ts` in same dir) is also acceptable.
- **Filename base**: match the file under test (`mcp.ts` → `mcp.test.ts`).

### 3.4 Config Files

- Pattern: `*.config.ts` (or `*.config.js` / `*.config.mjs` when TS is unsupported).
- Examples: `vitest.config.ts`, `electron.vite.config.ts`, `drizzle.config.ts`.

### 3.5 Type Declaration Files

- Pattern: `*.d.ts`, all-lowercase or `kebab-case`.
- Examples: `env.d.ts`, `global-types.d.ts`.

### 3.6 Markdown / Documentation

| Type | Convention | Example |
|---|---|---|
| Top-level meta docs at repo root | `UPPERCASE.md` | `README.md`, `CLAUDE.md`, `DESIGN.md`, `CONTRIBUTING.md` |
| Per-directory README | `README.md` (always uppercase) | `src/main/core/paths/README.md` |
| All other docs (under `docs/`, `packages/*/docs/`, etc.) | `kebab-case.md` | `database-testing.md`, `lan-transfer-protocol.md` |

### 3.7 JSON / YAML / TOML

- `package.json`, `tsconfig.json`: tool-mandated names; do not customize.
- Project-specific config JSON: `kebab-case.json` (`turbo.json` is an exception — tool-mandated).

---

## 4. Directory Naming

Directory naming splits into category rules (§4.1–§4.3, §4.5–§4.7, §4.10) and cross-cutting rules: §4.4 (file vs subdirectory), §4.8 (top-level closed), §4.9 (singular vs plural).

### 4.1 npm Package Directories — `kebab-case`

`packages/*` directory names must be `kebab-case`. The directory name must equal the `name` field in `package.json` (minus the scope prefix).

```
packages/ai-sdk-provider/      ✅
packages/mcp-trace/            ✅
packages/extension-table-plus/ ✅
packages/somePkg/              ❌ (camelCase not allowed)
packages/SomePkg/              ❌ (PascalCase not allowed)
```

### 4.2 Business React Component Directories — `PascalCase`

When a directory **is** a component (i.e. contains the component's named file such as `Sidebar.tsx`, or groups files under one component name), use `PascalCase`.

```
src/renderer/components/Sidebar/         ✅
src/renderer/components/CodeEditor/      ✅
src/renderer/components/MarkdownEditor/  ✅
```

### 4.3 Bucket Directories — `lowercase plural noun`

"Bucket" = a categorical container holding many unrelated items of the same kind.

```
services/   utils/   hooks/   components/   pages/   types/
```

Bucket names are **plural** (see §4.9 for singular-vs-plural rules across all directory kinds). Do **not** invent variants like `Services/` or `helpers-and-utils/`.

### 4.4 File-Level vs Subdirectory Organization Inside a Bucket

Inside any bucket or domain directory, a **single file is the default**. Promote to a subdirectory only when the topic requires multiple files.

| Situation | Layout | Examples |
|---|---|---|
| One file can express the entire capability / topic | One `.ts` file | `services/CacheService.ts`, `utils/assistant.ts`, `hooks/useChatContext.ts` |
| Implementation is too large for one file, **or** the topic owns several closely related artifacts (helpers, types, sub-files) that belong together | A subdirectory grouping the files | `services/messageStreaming/`, `services/ocr/`, `utils/markdown/`, `hooks/translate/` |

Do not pre-create a subdirectory for anticipated growth — promote only when the second file actually arrives.

### 4.5 Business / Domain Module Directories — `camelCase`

When a directory represents a **named domain** (a coherent business module with its own internal structure), use `camelCase`.

```
src/main/ai/streamManager           ✅
src/main/services/fileProcessing/   ✅
```

Placement — whether a domain module lives as a top-level `features/<domain>/` or as a subdirectory inside a bucket like `services/` — is governed by §4.10; this section governs only its name.

### 4.6 shadcn / `packages/ui` Directories — `kebab-case`

Everything inside `packages/ui/` (both files and directories) follows shadcn conventions:

```
packages/ui/src/components/primitives/        ✅
packages/ui/src/components/primitives/button-group/  ✅
```

### 4.7 Convention-Mandated Directories

These have fixed names dictated by tools or community convention:

| Directory | Purpose |
|---|---|
| `__tests__/` | Test files (Jest/Vitest convention) |
| `__mocks__/` | Mock files (Jest/Vitest convention) |
| `node_modules/` | Dependencies (npm) |
| `dist/`, `build/`, `out/` | Build output |

### 4.8 Top-Level Directories — Closed by Default

The set of top-level directories under each of:

- repository root `/`
- `/src/`
- `/src/main/`, `/src/renderer/`, `/src/preload/`
- `/src/shared/`

is **closed by default**. Adding one is a structural commitment.

**A new top-level directory MAY be added only when the PR description establishes both:**

1. **Necessity** — no existing top-level bucket can host the new files without semantic loss.
2. **Completeness** — the new directory has a clear scope, follows §4.3 (plural bucket) or §4.5 (singular domain module) form, and does not overlap with any existing bucket.

If either is in doubt, place the files inside an existing bucket. Subdirectories under existing buckets are unrestricted.

For the per-root applications of this rule, see [Main Process Architecture §4](./main-process-architecture.md) (`/src/main/`), [Renderer Architecture §6](./renderer-architecture.md) (`/src/renderer/`), and [Shared Layer Architecture §2](./shared-layer-architecture.md) (`/src/shared/`).

### 4.9 Singular vs Plural

Choose number based on what the directory **conceptually contains**, not on which sounds nicer.

| Directory role | Number | Examples |
|---|---|---|
| **Collection bucket** — holds many items of the same kind | **plural** | `services/`, `utils/`, `hooks/`, `components/`, `pages/`, `types/`, `models/`, `shortcuts/`, `agents/` |
| **Namespace / theme** — represents one subject area, not a collection | **singular** | `config/`, `data/`, `auth/`, `api/`, `ipc/`, `file/` |
| **Business / domain module** — named action or concept | **singular** (default) | `apiServer/`, `fileProcessing/`, `webSearch/`, `bootConfig/` |
| **Component directory** (dir = component) | follows the **component name** | `Avatar/`, `CodeEditor/` (singular component); `SearchResults/` (component representing a group) |

Decision rule: ask "does this directory hold **many of X**?" — yes → plural; no → singular. When two readings both make sense, pick the one that matches the directory's **default import name** (e.g. `import { ... } from './config'` reads naturally with `config/` singular).

**Same stem, different number — decide by role, not by the word.** A name like `agent` is not inherently singular or plural; its number follows the role the directory plays. The `agents/` listed above is the **collection-bucket** reading — e.g. `src/main/ai/agents/`, which holds many agent implementations (`builtin/`, `cherryclaw/`, …). The same stem is **singular** when the directory is a feature **namespace** that groups one feature's code rather than many agents — `src/renderer/hooks/agent/` (holds the agent feature's hooks, not agents) and `src/renderer/components/chat/agent/` are singular, matching their sibling namespaces (`hooks/chat/`, `hooks/tab/`, `hooks/translate/`). Reading the `agents/` entry as "the word *agent* is always plural" is the trap: apply the decision rule to the directory's actual contents.

### 4.10 Feature Modules — `features/` vs Type Buckets

A **feature module** is a self-contained domain directory under a process root's `features/` bucket — `src/main/features/` and `src/renderer/features/` — that co-locates *everything* one domain owns: its services or components, domain-local utils and hooks, and any adapters, routes, or other domain-specific helpers, in one tree.
`features/` is itself a bucket (lowercase plural, §4.3); each module inside is a `camelCase` domain directory (§4.5).

**A domain earns a `features/<domain>/` home only when it is large, complex, and multi-file** — cohesion alone is not enough.

| The domain is… | Home | Layout |
|---|---|---|
| Large / complex — spans more than one concern (e.g. a service plus its own adapters, routes, utils) | `features/<domain>/` | self-contained tree; the service class lives inside it (§5.2) |
| Headless multi-file capability — a service plus its **private, topic-specific** satellites (adapters, stateless helpers, per-instance classes); no UI | `services/<topic>/` | one curated `index.ts` barrel; internals private and exempt from shape routing ([Renderer Architecture §3.1](./renderer-architecture.md)) |
| One cohesive service, even if domain-specific | `services/<Domain>Service.ts` | a single file — private helpers stay **inline**; a **generic** helper → `utils/<topic>.ts`; its first **topic-specific** satellite file → grow into `services/<topic>/` (row above) |
| A small cross-domain / standalone helper | `services/` or `utils/` | a single file |

This is the §4.4 promotion rule applied at the top level: a domain graduates in steps — a single file → a `services/<topic>/` topic directory → its own `features/` module — only as the additional files actually arrive and span more than one concern.
Do not pre-create a `features/<domain>/` for an anticipated module.
`features/` holds high-cohesion domain code; the sibling type-buckets (`services/` + `utils/` in main; `components/` + `hooks/` + `services/` + `utils/` in the renderer) hold everything below that bar — single-file pieces and `services/<topic>/` capabilities.
A large, multi-file domain left scattered across the `services/` and `utils/` buckets instead of gathered into one `features/<domain>/` is the §6.7 scattered/impure anti-pattern.

**Canonical example** — `src/main/features/apiGateway/`:

```
features/apiGateway/
├── ApiGatewayService.ts   # the domain service (§5.2)
├── adapters/              # domain-specific sub-modules
├── middleware/
├── routes/
└── utils/                 # domain-local utils, not the global src/main/utils/ bucket
```

For the main process, [Main Process Architecture](./main-process-architecture.md) covers `features/` vs the type-buckets (`services/` / `utils/`) and the dependency direction; for the renderer, [Renderer Architecture](./renderer-architecture.md) places `features/` within the full layering (windows → pages → features → components → packages/ui), with per-directory responsibilities and dependency rules.

---

## 5. Identifier Naming

Names inside source code — separate axis from filenames.

| Identifier kind | Convention | Example |
|---|---|---|
| Component, Class, Interface, Type alias, Enum type | `PascalCase` | `class KnowledgeService`, `interface UserConfig`, `type Status` |
| Variable, function, method, parameter | `camelCase` | `fetchUser`, `isReady` |
| Hook | `camelCase` with mandatory `use` prefix | `useChatContext` |
| Constant, enum member | `UPPER_SNAKE_CASE` | `MAX_RETRY_COUNT`, `IpcChannel.GetConfig` |
| Private class member | no `_` prefix; use `private` modifier | `private cache` |
| Generic type parameter | `PascalCase`, prefer descriptive | `<TItem>`, `<TError>` (avoid bare `T` for non-trivial cases) |

### 5.1 Singular vs Plural in Identifiers

| Identifier kind | Number | Example |
|---|---|---|
| Class, interface, type alias, enum type | **singular** | `User`, `OrderItem`, `LogLevel` (not `Users`, `OrderItems`) |
| Variable / property holding a single value | **singular** | `const user = ...`, `currentOrder` |
| Variable / property holding a collection (array, `Map`, `Set`) | **plural** | `const users = [...]`, `orderItems`, `connectedClients` |
| Boolean | no plural; use `is` / `has` / `can` / `should` prefix | `isReady`, `hasPermission`, `canEdit`, `shouldRetry` |
| Function returning one item | **singular** verb phrase | `getUser(id)`, `findOrder()` |
| Function returning many items | **plural** noun in name | `getUsers()`, `listOrders()`, `fetchPendingJobs()` |
| Function that mutates a collection | verb + plural object | `addUsers(...)`, `removeTags(...)` |
| Event / handler name | follows the event subject | `onMessageReceived` (one), `onItemsLoaded` (many) |

### 5.2 Suffix for Stateful Singleton Capabilities — `Service` (default) / `Manager` (instance pool)

A module that owns **retained module-level state, resources, or a lifecycle** — a **singleton capability** — MUST be implemented as a class managed as a singleton (two valid forms — see below) and take exactly one of two suffixes:

| Suffix | Use when the class… | Examples |
|---|---|---|
| `Service` | Provides a cohesive **domain capability / API surface**. The **default** for any singleton capability. | `CacheService`, `DataApiService`, `FileService`, `ExportService` |
| `Manager` | Owns and coordinates a **pool / registry of many homogeneous instances**, and that coordination is its defining job. | `WindowManager` (window pool), `TabLruManager` |

**Decision rule:** ask "is this class's primary job to own and coordinate a *set of many like instances*?" — yes → `Manager`; otherwise → `Service` (default when unsure).

A `Service` / `Manager` class lives where its domain ownership lies (e.g. `src/main/data/CacheService.ts`, `src/main/core/window/WindowManager.ts`); placement under `services/` is not required.

**The criterion is statefulness, not mechanism.** Module-scope mutable bindings, closure-held registries, and retained top-level third-party instances (`const listeners = new Map()`, `export const emitter = new Emittery()`) qualify exactly as class fields do — normalize them into the class + singleton + suffix form instead of keeping a plain name: a plain camelCase name asserts statelessness (routing table below).

**What counts as state** — values retained **across calls** that change observable behavior. Not state: a transparent perf cache (memoization that changes only latency), and transient in-flight values confined to a single async flow (e.g. a listener registered and removed within one operation).

**Multi-instance helper classes take no suffix.** A class with per-instance state, instantiated by its consumers (a tokenizer, a transport, a subscription — `ShikiStreamTokenizer`, `IpcChatTransport`, `TopicStreamSubscription`), is not a singleton capability: name it a plain `PascalCase` descriptive noun. The suffix marks the singleton-capability **role**, not the presence of fields.

**Stateless modules are NOT classes for this rule** — pure function collections, queries, conversions, and SDK wrappers without retained state stay plain modules and do not receive a `Service` / `Manager` suffix.

**If a module looks like it wants to be a `Service` but is not a stateful singleton capability, route it — ownership first, then shape.** A module consumed by exactly **one** owner co-locates with that owner (feature internals, or a private satellite behind a `services/<topic>/` barrel — [Renderer Architecture §3.1](./renderer-architecture.md), [Main Process Architecture](./main-process-architecture.md)) and skips this table. The table routes **shared** modules; stateless shared modules default to `utils/`:

| Actual shape of the module | Right home | Naming |
|---|---|---|
| Stateless helper — computes values (queries, conversions, predicates, formatters); **reads** via downward infra (`data` / `ipc`) are fine | `utils/` (or feature-local `utils/` subdirectory) — the **default** for stateless shared modules | `<topic>.ts` (camelCase; no `Utils` suffix — see §3.2) |
| Stateless module with **outward side effects** (opens windows / popups, writes the clipboard, fires app events, performs `data` / `ipc` **writes**, drives other subsystems; logging does not count) — or **dependency-forced** out of `utils/` (must import `services/`, which `utils/` may not) | `services/` (or feature-local `services/`) — state the reason in the PR | `<topic>.ts` (camelCase; **no** `Service` suffix — it is not a stateful class) |
| Multi-instance stateful helper class | co-located with its consumer (topic dir / feature), or `services/` | `PascalCase` descriptive noun, **no suffix** (`IpcChatTransport`) |
| Depends on React lifecycle / state / context | `hooks/` (or co-located with the consuming feature) | `useXxx.ts` (the `use` prefix is the role marker — see §3.2) |
| Renders JSX / owns view markup | `components/` (shared) or `pages/` (route-bound) | `Xxx.tsx` (PascalCase — see §3.1) |
| Single-call pass-through to `window.api.*` | inlined at the call site | (no file) |

#### Two valid forms of a `Service`

The `Service` suffix names a **role** (a stateful domain capability), not a **mechanism**. A class earning the suffix may be implemented as either:

| Form | Pattern | Used when |
|---|---|---|
| Lifecycle service | `@Injectable('XxxService')` + `extends BaseService`, accessed via `application.get('XxxService')` | The service owns long-lived resources OR registers persistent side effects |
| Direct-import singleton service | `export const xxxService = new XxxService()` | No long-lived resources, no persistent side effects, but still has class-level state (e.g. cached SDK instances) |

The criteria for choosing between them are defined in [`docs/references/lifecycle/lifecycle-decision-guide.md`](lifecycle/lifecycle-decision-guide.md).

### 5.3 Drizzle Schema Inferred Row Types

Every Drizzle table in `src/main/data/db/schemas/` exports its inferred select/insert types using the **`Row` suffix** form:

| Inferred from | Type name | Example |
|---|---|---|
| `xxxTable.$inferSelect` | `XxxRow` | `AgentRow`, `McpServerRow` |
| `xxxTable.$inferInsert` | `InsertXxxRow` | `InsertAgentRow`, `InsertMcpServerRow` |

```ts
export const mcpServerTable = sqliteTable('mcp_server', { /* ... */ })

export type McpServerRow = typeof mcpServerTable.$inferSelect
export type InsertMcpServerRow = typeof mcpServerTable.$inferInsert
```

`Row` names the raw database row and is deliberately distinct from the API entity type (`XxxEntity`, e.g. `WorkspaceEntity`) the row is mapped to in the shared layer. The `Xxx` stem matches the table-derived `xxxTable` const (see §3.2), so `agent_workspace` → `agentWorkspaceTable` → `AgentWorkspaceRow` / `InsertAgentWorkspaceRow`.

Do **not** use the alternatives that previously coexisted here: `XxxSelect` / `XxxInsert`, `Xxx` / `NewXxx`, or Drizzle's docs-style `SelectXxx` / `InsertXxx`. The `Row` suffix is chosen over Drizzle's docs form precisely because it keeps the DB-row type visibly separate from the API `XxxEntity` type.

---

## 6. Edge Cases

### 6.1 Acronyms and Initialisms

When an acronym (API, URL, ID, HTTP, MCP, AI) appears inside `PascalCase` or `camelCase`:

- **First letter uppercase, rest lowercase** — `HttpClient`, `UserId`, `ApiServer`, `McpService`.
- **Never all-caps** — `HTTPClient`, `UserID`, `APIServer` are forbidden.
- **At the start of `camelCase`** — entirely lowercase: `httpClient`, `userId`, `apiServer`.
- **Same form applies to filenames** — `McpService.ts`, not `MCPService.ts`.

### 6.2 Case-Only Renames

`git` on macOS defaults to `core.ignorecase=true`, which silently swallows pure case-change renames. Always use the two-step pattern:

```bash
git mv Foo.tsx _tmp_foo.tsx
git mv _tmp_foo.tsx foo.tsx
```

### 6.3 Two Files Differing Only in Case

Forbidden. `Button.tsx` and `button.tsx` in the same directory will break on case-insensitive file systems.

### 6.4 Barrel / Index Files

A **barrel** is an `index.ts` (always lowercase) whose sole job is to re-export a directory's public surface. It is not a convenience: it **declares an encapsulation boundary** — the directory's other files are private, and every outside importer goes through the barrel. This section is the single authority for barrels across all four processes; the per-process docs ([Shared §3.1](./shared-layer-architecture.md), [Main §2.1](./main-process-architecture.md), [Renderer §3.1/§5](./renderer-architecture.md)) *apply* it, they do not restate it.

**The `index` filename is reserved for barrels, and a barrel is always `index.ts`.** A directory's own implementation — including its main component — lives in a named file (`RichEditor.tsx`, never `RichEditor/index.tsx`); a pure re-export has no JSX, so a barrel is never `.tsx`. An `index.tsx` is therefore always a violation, with no exceptions: a barrel that should be `.ts`, an implementation that should be a named file, or a TanStack index route that should use the flat dot form (`<segment>.index.tsx`, §6.6) — there the `index` token is a path segment, never the filename.

Rules 1–3 are lint-enforced; rule 4 is a review judgment.

1. **Re-export only** — explicit named re-exports, nothing else: no `export *`, no `export default` implementation, no local declarations, no logic. (`export *` destroys the curated surface and tree-shaking; a barrel carrying logic is a module wearing a door's name.)
2. **Enforced sole entry, or no barrel** — a barrel is real only if lint forbids outside code from deep-importing the directory's internals. **A directory whose internals cannot be closed off should not have a barrel**: an unenforced door is worse than none — two entry surfaces to maintain, and the leak returns.
3. **No nesting** — a barrel must not re-export another barrel. A parent directory that merely aggregates independent sub-modules gets no barrel; each cohesive sub-unit owns its own. (Hence the bucket roots `types/`, `utils/`, `services/` have no root `index.ts` — §4.8.)
4. **One cohesive unit, not an aggregator** — a barrel's exports are a connected API consumers take as a set. A directory holding several independently-consumed concerns should be split into separate boundaries or demoted to a no-barrel container. Not lint-checkable — a design call.

> **Orthogonal to tree-shaking.** Barrel hygiene bounds leakage but does not replace root `sideEffects`: a rule-clean barrel that exports both a light and a heavy symbol still drags the heavy subgraph into a light consumer unless the bundler can prove side-effect freedom. The two are separate layers; both are needed.

> **Dev builds don't tree-shake.** In dev, importing one symbol loads every module the barrel reaches, rule-clean or not. Rule 4 is what bounds this cost — a cohesive API is consumed as a set anyway; when one heavy member hurts a light consumer, split the boundary or code-split at the call site — never deep-import past the door.

> **Dynamic `import()` is an import.** Rule 2 applies unchanged: cross-boundary lazy loading enters through the barrel, never through an internal file; only code inside the boundary may lazy-load its own internals. (Renderer §5 shows the `React.lazy` form.)

### 6.5 Directory Name vs Package Name

In `packages/*`, the directory name and `package.json#name` (after stripping scope) must match exactly. Renaming one requires renaming the other.

### 6.6 TanStack Router File-Based Routes

Files under `src/renderer/routes/` are **kebab-case** — TanStack Router maps filename directly to URL.

Reserved tokens (TanStack-defined):

| Token | Meaning |
|---|---|
| `__root.tsx` | Root layout |
| `<segment>.index.tsx` | Index route — always the flat dot form (`settings.index.tsx`); a bare `index.tsx` is banned even here (§6.4) |
| `$<param>.tsx` | Dynamic segment (e.g. `$appId.tsx`) |
| `$.tsx` | Catch-all |

### 6.7 Bucket Anti-Patterns

A bucket directory drifts toward unhealth when **any** of these accumulate:

1. **Singular name on a directory that holds many like items** — should be a §4.3 bucket but was misclassified as a §4.9 namespace.
2. **Impure contents** — files inside the bucket that do not match the bucket's declared kind (e.g. a directory named after one React pattern that also holds wrapper components which do not use that pattern).
3. **Thin bucket** — a top-level bucket holding 0–2 files for an extended period is usually an over-eager extraction; reconsider whether it should be a subdirectory inside an existing bucket (see §4.8).
4. **Overlapping scope** — two top-level buckets whose names could each plausibly host the same file. One of them is redundant or the boundary is ill-defined.

Any of these signals warrants a consolidation review.

---

## 7. Decision Tree

```
Naming a new FILE
├─ React component (.tsx)?
│  ├─ Under src/renderer/routes/?  → kebab-case.tsx  (api-server.tsx)
│  ├─ Under packages/ui/?              → kebab-case.tsx  (button.tsx)
│  └─ Under src/renderer/?         → PascalCase.tsx  (Sidebar.tsx)
├─ React hook?                    → useXxx.ts       (useShortcuts.ts)
├─ Primary export is a class?     → PascalCase.ts   (KnowledgeService.ts)
├─ Primary export is function(s)? → camelCase.ts    (markdownConverter.ts)
├─ Type declaration?              → *.d.ts          (env.d.ts)
├─ Test?                          → *.test.ts(x)
├─ Config?                        → *.config.ts
└─ Documentation?
   ├─ Repo-root meta?             → UPPERCASE.md    (README.md)
   └─ Other?                      → kebab-case.md   (database-testing.md)

Naming a new DIRECTORY
├─ npm package (packages/*)?      → kebab-case      (ai-sdk-provider)
├─ Under packages/ui/?            → kebab-case      (primitives, button-group)
├─ Is itself a React component?   → PascalCase      (CodeEditor)
├─ Bucket / categorical container? → lowercase plural noun  (services, utils)
├─ Large/complex multi-file domain? → features/<camelCase>/  (apiGateway, §4.10)
├─ Business domain module?        → camelCase       (apiServer, fileProcessing)
└─ Unsure singular vs plural?     → see §4.9
```

---

## Appendix: References

This document distills consensus from:

- [Airbnb JavaScript Style Guide](https://github.com/airbnb/javascript) — file name matches default export
- [Google TypeScript Style Guide](https://google.github.io/styleguide/tsguide.html)
- [shadcn/ui conventions](https://github.com/shadcn-ui/ui) — kebab-case files, PascalCase exports
- [Next.js file-naming guidance](https://nextjs.org/docs)
- [typescript-eslint `naming-convention` rule](https://typescript-eslint.io/rules/naming-convention/)