docs(maintainers): add agent directives for types packages

Author: zimeg

AGENTS.md

@@ -91,6 +91,7 @@ npm run build --workspace=@slack/socket-mode
 
 Individual packages have their own `AGENTS.md` with package-specific guidance:
 
+- `packages/types/AGENTS.md` — shared type definitions, Block Kit types, event types
 - `packages/web-api/AGENTS.md` — adding API methods, code generation, client architecture
 
 ## Development Philosophy

packages/types/AGENTS.md

@@ -0,0 +1,95 @@
+# AGENTS.md — @slack/types
+
+Instructions for AI coding agents working on this package.
+
+## Package Overview
+
+Shared TypeScript type definitions for the Slack platform. Provides Block Kit elements, composition objects, event types, views, message attachments, message metadata, chunk types, and other common structures used across `@slack/*` packages.
+
+## Architecture
+
+### Source Layout
+
+```txt
+src/
+├── block-kit/                  # Block Kit UI framework types
+│   ├── block-elements.ts       # Interactive elements (buttons, menus, inputs, etc.)
+│   ├── blocks.ts               # Layout blocks (section, actions, context, etc.)
+│   ├── composition-objects.ts  # Text objects, option objects, filter objects, etc.
+│   └── extensions.ts           # Extended block types (e.g., for messages, modals)
+├── common/                     # Shared small types
+│   ├── bot-profile.ts          # Bot profile structure
+│   └── status-emoji-display-info.ts
+├── events/                     # Slack event type definitions
+│   ├── index.ts                # Barrel export for all event types
+│   └── *.ts                    # One file per event category (message, channel, user, etc.)
+├── calls.ts                    # Slack Calls types
+├── chunk.ts                    # Streaming chunk types
+├── dialog.ts                   # Legacy dialog types
+├── message-attachments.ts      # Message attachment types
+├── message-metadata.ts         # Message metadata types
+├── views.ts                    # Modal and Home tab view types
+└── index.ts                    # Root barrel export
+```
+
+### Key Design Principles
+
+- **Pure types** — this package contains only TypeScript type definitions (interfaces, type aliases, enums). No runtime code.
+- **Barrel exports** — `src/index.ts` re-exports everything. Consumers import directly from `@slack/types`.
+- **Discriminated unions** — Block Kit types use discriminated unions keyed on `type` (e.g., `KnownBlock`, `BlockElement`).
+
+## Critical Rules
+
+1. **All types are manually maintained** — there is no code generation in this package.
+2. **Export everything from `src/index.ts`** — every public type must be reachable from the barrel.
+3. **No runtime code** — this package must only contain type definitions, no JavaScript logic.
+
+## Naming Conventions
+
+- **Types/Interfaces**: PascalCase
+- **Block types**: `{Kind}Block` (e.g., `SectionBlock`, `ActionsBlock`)
+- **Element types**: `{Kind}Element` or `{Kind}Action` (e.g., `ButtonElement`, `StaticSelectAction`)
+- **Event types**: `{Category}{Action}Event` (e.g., `MessageChangedEvent`, `ChannelCreatedEvent`)
+- **Composition objects**: descriptive PascalCase (e.g., `PlainTextElement`, `MrkdwnElement`, `Option`, `ConfirmationDialog`)
+
+## Adding New Types
+
+### Adding a New Block Kit Element
+
+1. Add the interface to the appropriate file in `src/block-kit/`:
+   - **Layout blocks** → `blocks.ts`
+   - **Interactive elements** → `block-elements.ts`
+   - **Composition objects** → `composition-objects.ts`
+   - **Message/modal extensions** → `extensions.ts`
+2. Add the new type to the relevant discriminated union (e.g., `KnownBlock`, `BlockElement`).
+3. Verify it is exported through `src/index.ts` (already covered if the file is re-exported).
+
+### Adding a New Event Type
+
+1. Find or create the appropriate category file in `src/events/` (e.g., `channel.ts`, `message.ts`).
+2. Define the event interface following existing patterns in that file.
+3. Export the new type from `src/events/index.ts`.
+
+### Adding a New Top-Level Type Category
+
+1. Create a new `.ts` file in `src/`.
+2. Add the `export * from './<filename>'` line to `src/index.ts`.
+
+## Testing
+
+```bash
+npm test --workspace=packages/types         # build + type tests
+npm run test:types --workspace=packages/types # tsd only
+```
+
+- **Test framework**: tsd (type-level testing only)
+- **Test files**: `test/*.test-d.ts`
+- **No unit tests** — since there is no runtime code, only type-level tests are needed.
+
+Use `expectType`, `expectAssignable`, `expectError`, and `expectNotAssignable` from tsd to validate type correctness.
+
+## Common Pitfalls
+
+- **Discriminated union membership** — when adding a new block or element type, forgetting to add it to the union type (e.g., `KnownBlock`) means it won't be recognized in typed arrays like `KnownBlock[]`.
+- **Downstream impact** — types defined here are consumed by `@slack/web-api`, `@slack/webhook`, `@slack/socket-mode`, and other packages. Breaking changes require coordination.
+- **Optional vs. required fields** — match the Slack API documentation. Fields that are always present in API responses should be required; fields that are conditionally present should be optional.