Output Directives

Overview

Agents can control platform-specific message delivery by prefixing their output with [[key:value]] directives. OAB parses and strips these before sending to the platform.

Format

[[reply_to:1502606076451885136]]
[[ephemeral:true]]              ← future
Actual message content starts here...

Rules:

• Consecutive [[key:value]] lines at the start of output = directive header block
• First line that doesn't match [[key:value]] (with colon) = content begins
• [[X]] without colon is NOT a directive — stops parsing, preserved as content
• Directives are stripped from the final message (never visible to users)
• Unknown keys are silently ignored (forward compatible, logged at debug level)
• If the same key appears multiple times, the last value wins

Available Directives

reply_to

Reply to a specific message by ID (Discord: message_reference).

[[reply_to:1502606076451885136]]
Here is my reply to that specific message.

Value: Platform message ID. Format depends on the target adapter — Discord requires a numeric snowflake; Slack accepts ts (e.g. 1234567890.123456). The directive parser validates that the value is non-empty, ≤64 chars, and contains only ASCII alphanumeric characters plus ., -, _; per-platform format validation happens in each adapter.

Behavior:

• Discord: sends with message_reference, showing the native "replying to..." UI
• Feishu: sends via Reply API (POST /im/v1/messages/{id}/reply), showing native quote UI
• Invalid/non-existent message ID: silently falls back to plain send
• Works in both streaming and send-once modes

How agents get message IDs: Every incoming message includes message_id in SenderContext:

{
  "schema": "openab.sender.v1",
  "sender_id": "845835116920307722",
  "sender_name": "pahud.hsieh",
  "message_id": "1502606076451885136",
  "channel": "discord",
  ...
}

Multi-Agent Use Case

In a thread with multiple bots, agents can reply to each other's messages:

Human: "Review this PR" (message_id: 100)
Bot A: "Found 3 issues" (message_id: 101)
Bot B output:
  [[reply_to:101]]
  I agree with Bot A on F1, but F2 is actually fine because...

This creates clear visual conversation threads within a Discord thread — essential for multi-agent collaboration.

Comparison with Other Platforms

Platform	Reply Mechanism	Agent Control
OpenClaw	replyToMode config (off/first/all)	❌ Platform decides, always to trigger msg
Hermes Agent	DISCORD_REPLY_TO_MODE env var	❌ Platform decides, always to trigger msg
OAB	[[reply_to:message_id]] directive	✅ Agent chooses any message

Note: reply_to is currently implemented for Discord and Feishu (gateway). Slack message IDs (ts format like 1234567890.123456) are accepted by the parser but the Slack adapter does not yet send threaded replies via this directive — it falls back to plain send. Slack support can be added in a future PR.