feat: add typing indicator support via IMCore private framework

[kohoj]

Summary

Implements typing indicators for outgoing messages (closes #22) using runtime dynamic loading of Apple's IMCore private framework. This is the only way to programmatically send typing indicators — AppleScript has no equivalent capability.

What's included

1. IMsgCore — TypingIndicator struct

• startTyping(chatIdentifier:) — show the "..." typing bubble on the recipient's device
• stopTyping(chatIdentifier:) — dismiss the typing bubble
• typeForDuration(chatIdentifier:duration:) — show for N seconds, then auto-stop
• Uses dlopen to load /System/Library/PrivateFrameworks/IMCore.framework at runtime
• Connects to IMDaemonController, resolves chat via IMChatRegistry, then calls [IMChat setLocalUserIsTyping:]

2. CLI — imsg typing command

# Start typing indicator (stays until timeout or --stop)
imsg typing --to +14155551212

# Show for a specific duration
imsg typing --to +14155551212 --duration 5s

# Stop typing indicator
imsg typing --to +14155551212 --stop true

# Target by chat identifier directly
imsg typing --chat-identifier "iMessage;-;+14155551212"

# JSON output
imsg typing --to +14155551212 --json

Supports all the same chat targeting as send: --to, --chat-id, --chat-identifier, --chat-guid.

3. RPC — typing.start / typing.stop methods

{"jsonrpc":"2.0","id":1,"method":"typing.start","params":{"to":"+14155551212"}}
{"jsonrpc":"2.0","id":2,"method":"typing.stop","params":{"to":"+14155551212"}}

Also supports chat_identifier, chat_guid, chat_id, and service params.

How it works

The implementation uses the same approach as BlueBubbles — loading IMCore at runtime via dlopen/objc_getClass/sel_registerName. The core call is:

[chat setLocalUserIsTyping:YES];  // start
[chat setLocalUserIsTyping:NO];   // stop

No new dependencies are required. The private framework is available on all macOS versions that support Messages.app.

Files changed

File	Change
Sources/IMsgCore/TypingIndicator.swift	New — core typing indicator logic
Sources/IMsgCore/Errors.swift	Add typingIndicatorFailed error case
Sources/imsg/Commands/TypingCommand.swift	New — CLI command
Sources/imsg/CommandRouter.swift	Register typing command
Sources/imsg/RPCServer.swift	Add typing.start/typing.stop RPC methods

Caveats

• Private API: Uses IMCore private framework. Not suitable for Mac App Store distribution, but fine for CLI tools and side-loaded apps.
• Requires active conversation: The chat must already exist in Messages.app (same as send).
• Daemon connection: First call has ~500ms latency for IMDaemonController connection setup; subsequent calls are fast.

Testing

• swift build passes with zero errors and zero warnings
• Manual testing: imsg typing --to <number> shows the typing bubble on the recipient's iPhone
• Existing tests are unaffected (pre-existing Testing framework issue on non-Xcode-16 environments)