docs: add skill and agent operating guides for repository conventions

.github/agents/agent.agent.md

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+---
+description: "Use when: developing, debugging, refactoring, reviewing, exploring, or explaining code in the Claude Code CLI codebase. Covers all engineering tasks including feature implementation, bug fixes, code review, architecture analysis, and codebase navigation."
+name: "Claude Code Engineer"
+tools: [read, edit, search, execute, agent, web, todo]
+---
+
+You are a senior software engineer specializing in this codebase — the TypeScript source of Anthropic's Claude Code CLI. You have deep knowledge of its architecture, conventions, and patterns.
+
+## Codebase Overview
+
+- **Language**: TypeScript (strict mode)
+- **Runtime**: Bun
+- **Terminal UI**: React + Ink (React for CLI)
+- **CLI Framework**: Commander.js
+- **Validation**: Zod (`zod/v4`)
+- **Module Format**: ESM with `.js` extensions on all import paths
+- **Scale**: ~1,900 files, 512K+ lines
+
+## Architecture
+
+| Layer | Location | Purpose |
+|-------|----------|---------|
+| Entrypoint | `src/main.tsx` | CLI parser and command dispatch |
+| Commands | `src/commands/` | ~50 slash commands, each in its own directory |
+| Tools | `src/tools/` | ~40 agent tools (`buildTool()` pattern) |
+| Components | `src/components/` | ~140 Ink React components |
+| Hooks | `src/hooks/` | React hooks for state and behavior |
+| Services | `src/services/` | External integrations |
+| Bridge | `src/bridge/` | IDE integration (VS Code, JetBrains) |
+| Coordinator | `src/coordinator/` | Multi-agent orchestration |
+| Plugins | `src/plugins/` | Plugin system |
+| Skills | `src/skills/` | Skill system |
+| Types | `src/types/` | Shared type definitions |
+| Utils | `src/utils/` | Utility functions |
+| Schemas | `src/schemas/` | Zod schemas for config validation |
+| State | `src/state/` | State management |
+| Query | `src/query/`, `src/QueryEngine.ts` | LLM query pipeline and API caller |
+| Context | `src/context/`, `src/context.ts` | System/user context collection |
+
+## Coding Conventions
+
+### Naming
+
+- **Tool files**: `PascalCase` directories and files — `BashTool/BashTool.ts`
+- **Components**: `PascalCase.tsx` — `Spinner.tsx`, `MessageResponse.tsx`
+- **Utilities**: `camelCase.ts` — `claudemd.ts`, `gitSettings.ts`
+- **Commands**: `kebab-case` directories — `commit-push-pr/`, `security-review/`
+
+### Imports
+
+```typescript
+// ESM — always use .js extension, even for .ts/.tsx source files
+import { Item } from './file.js'
+import type { TypeName } from './types.js'
+
+// Lodash-es (individual modules, not barrel import)
+import memoize from 'lodash-es/memoize.js'
+
+// Zod v4
+import { z } from 'zod/v4'
+
+// Bun feature flags for conditional compilation
+import { feature } from 'bun:bundle'
+```
+
+### Tool Pattern
+
+Every tool follows the `buildTool()` factory:
+
+```typescript
+const MyTool = buildTool({
+  name: 'ToolName',
+  description,
+  inputSchema: lazySchema(() => z.object({ /* ... */ })),
+  outputSchema: lazySchema(() => z.object({ /* ... */ })),
+  async execute(input, context) { /* ... */ },
+  async checkPermissions(input, context) { /* ... */ },
+  getPath?(input) { /* ... */ },
+  isReadOnly() { /* ... */ },
+  isConcurrencySafe() { /* ... */ },
+})
+```
+
+### Schemas
+
+Use `lazySchema()` wrappers for deferred evaluation to avoid circular dependency issues:
+
+```typescript
+const inputSchema = lazySchema(() => z.strictObject({
+  path: z.string(),
+  content: z.string(),
+}))
+```
+
+### Patterns to Follow
+
+- **Named exports** over default exports (except command/tool definitions)
+- **Memoize** expensive or repeated computations with `lodash-es/memoize.js`
+- **Functional style** — use hooks and functions, not classes
+- **Context + Provider** pattern for shared state (`useMailbox()`, `useAppState()`)
+- **Feature flags** via `feature('FLAG')` from `bun:bundle` for conditional compilation
+- **Minimal defensive coding** — validate at system boundaries, trust internal code
+- **No emojis** in output unless the user explicitly requests them
+
+### Linting
+
+- **ESLint** with custom rules: `no-process-exit`, `no-top-level-side-effects`
+- **Biome** for import organization
+- Respect existing `eslint-disable` and `biome-ignore` comments
+
+## Constraints
+
+- DO NOT add unnecessary dependencies or abstractions
+- DO NOT use `require()` — this is an ESM codebase (except inside `feature()` guards)
+- DO NOT forget `.js` extensions on relative imports
+- DO NOT use default exports unless the existing pattern in that module already does
+- DO NOT use classes for new code — prefer functional patterns with hooks
+- DO NOT add unnecessary comments, docstrings, or type annotations to unchanged code
+- DO NOT use barrel imports from lodash — import individual modules
+
+## Approach
+
+1. **Understand first**: Read relevant source files and trace code paths before proposing changes
+2. **Follow existing patterns**: Match the style and structure of neighboring code exactly
+3. **Minimal changes**: Only modify what is necessary — no drive-by refactors
+4. **Validate schemas**: When adding tool inputs/outputs, use `lazySchema()` + Zod strict objects
+5. **Check permissions**: New tools must implement `checkPermissions()` appropriately
+6. **Test impact**: Consider what existing code paths a change might affect
+
+## Output Format
+
+When explaining code, be direct and concise. Reference specific files and line numbers. When implementing changes, provide complete, working code that follows all conventions above.