[BUG] Channel plugin silently fails when --channels flag is omitted

Summary

When a channel plugin (e.g., Discord) is installed but the session is started without --channels, inbound messages are silently dropped with no error or warning. The bot appears to work (typing indicator shows briefly) but notifications never reach the session.

Steps to Reproduce

1. Install the Discord plugin: /plugin install → discord@claude-plugins-official
2. Configure the bot token: /discord:configure <token>
3. Complete pairing and set allowlist policy
4. Start a new session without --channels:

``bash
claude
``

1. /reload-plugins confirms: 1 plugin MCP server — looks healthy
2. Send a DM to the bot from Discord

Expected Behavior

Either:

• The message arrives in the session, OR
• A clear warning/error explains that --channels is required for inbound notifications

Actual Behavior

• The bot receives the DM (confirmed via ps and lsof — Gateway TCP connection active)
• Discord shows "Bot is typing..." for ~2 seconds, then it disappears
• No error in stderr, no warning in the session, no notification
• The message is silently lost
• MCP tools (reply, fetch_messages) work fine — only inbound notifications are broken

Why This Is Confusing

The debugging surface is completely clean:

• /reload-plugins reports 1 plugin MCP server ✅
• Bot process is running (bun server.ts) ✅
• Discord Gateway is connected (TCP ESTABLISHED to Discord CDN) ✅
• MCP stdio pipe is connected (Unix socket to Claude Code PID) ✅
• sendTyping() succeeds (typing indicator appears) ✅
• mcp.notification() is called without throwing ✅
• Zero errors anywhere — the failure is completely silent

The root cause is that mcp.notification() sends the notification over stdio, but Claude Code doesn't process it as a channel notification without --channels. There is no feedback loop to tell the plugin (or the user) that notifications are being ignored.

Proposed Fix

When a plugin MCP server sends notifications/claude/channel but no channels are active (i.e., --channels was not passed), Claude Code should:

1. Log a warning to the session: _"Channel notification received from 'discord' but no channels are active. Start with --channels plugin:discord@claude-plugins-official to enable."_
2. Optionally, surface this in /reload-plugins output: _"Note: 'discord' is a channel plugin. Start with --channels to receive inbound messages."_

Related Issues

• #37139 — notifications dropped when session is idle (different: that's about idle sessions; this is about missing --channels flag entirely)
• #36986 — liveness indicator for channels (complementary)

Environment

• Claude Code v2.1.81
• macOS
• Plugin: discord@claude-plugins-official v0.0.1