feat: add Slack adapter with multi-platform ChatAdapter architecture

Introduces a platform-agnostic adapter layer (ChatAdapter trait + AdapterRouter)
that decouples session management, streaming, and reactions from any specific
chat platform. Refactors Discord support to implement this trait and adds a
new Slack adapter using Socket Mode (WebSocket) with auto-reconnect.

- Extract ChatAdapter trait with send/edit/thread/react methods + message_limit()
- Extract AdapterRouter with shared session routing, edit-streaming, and reactions
- Decouple StatusReactionController from serenity types (uses Arc<dyn ChatAdapter>)
- Implement DiscordAdapter (ChatAdapter for Discord via serenity)
- Implement SlackAdapter (ChatAdapter for Slack via reqwest + tokio-tungstenite)
- Add [slack] config section (bot_token, app_token, allowed_channels, allowed_users)
- Support running Discord + Slack simultaneously in one process
- Session keys namespaced by platform (discord:xxx, slack:xxx)
- Unicode emoji → Slack short name mapping for reactions

Relates to openabdev#93, openabdev#94, openabdev#86

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 2 people

Cargo.lock

@@ -14,7 +14,10 @@ serenity = { version = "0.12", default-features = false, features = ["client", "
 uuid = { version = "1", features = ["v4"] }
 regex = "1"
 anyhow = "1"
+async-trait = "0.1"
+futures-util = "0.3"
 rand = "0.8"
 reqwest = { version = "0.12", default-features = false, features = ["rustls-tls", "multipart", "json"] }
 base64 = "0.22"
 image = { version = "0.25", default-features = false, features = ["jpeg", "png", "gif", "webp"] }
+tokio-tungstenite = { version = "0.21", features = ["rustls-tls-webpki-roots"] }

Cargo.toml

@@ -1,8 +1,16 @@
+# Enable one or more adapters. At least one [discord] or [slack] section is required.
+
 [discord]
 bot_token = "${DISCORD_BOT_TOKEN}"
 allowed_channels = ["1234567890"]
 # allowed_users = ["<YOUR_DISCORD_USER_ID>"]  # empty or omitted = allow all users
 
+# [slack]
+# bot_token = "${SLACK_BOT_TOKEN}"     # Bot User OAuth Token (xoxb-...)
+# app_token = "${SLACK_APP_TOKEN}"     # App-Level Token (xapp-...) for Socket Mode
+# allowed_channels = ["C0123456789"]   # Slack channel IDs
+# allowed_users = ["U0123456789"]      # Slack user IDs (optional)
+
 [agent]
 command = "kiro-cli"
 args = ["acp", "--trust-all-tools"]