Problem

Plugins that hook agent_end (e.g. for cron output injection) need to persist messages into other sessions' transcripts. Currently, the only cross-session injection API available to plugins is enqueueSystemEvent, which is in-memory only and ephemeral.

This creates a fundamental limitation:

• enqueueSystemEvent queues events in memory, consumed only when the target session is activated
• Many sessions (e.g. Discord channel sessions that only receive cron announce delivery) are never activated — no user messages, no heartbeat targeting them
• If the gateway restarts before the session activates, all queued events are lost
• Even if events survive, they can accumulate unboundedly and overflow the context window on the next activation

Use Case: Cron Output → Channel Session Context

OpenClaw cron jobs with sessionTarget: "isolated" produce output delivered to Discord channels via announce mode. This delivery sends a Discord message but does not enter the target channel's persistent session context. The channel session never "remembers" what its cron jobs produced.

A plugin hooking agent_end can detect cron completions, extract the output, and should be able to persist it into the target channel's session transcript — so that when the session is eventually activated, the cron output is already in its conversation history.

Proposed Solution

Expose appendAssistantMessageToSessionTranscript (or a similar write API) through api.runtime.agent.session in the plugin runtime:

// In PluginRuntimeCore.agent.session:
appendMessageToTranscript: (params: {
  sessionKey: string;
  text: string;
  role?: "assistant" | "user";  // default: "assistant"
  idempotencyKey?: string;
}) => Promise<{ ok: boolean; reason?: string }>;

This would allow plugins to:

• Persist messages directly to the JSONL transcript file
• Target any session by sessionKey
• Survive gateway restarts (on-disk persistence)
• Be consumed naturally when the session is next loaded

Alternatives Considered

1. enqueueSystemEvent — in-memory only, lost on restart, requires session activation to consume
2. Dynamic import of internal transcript module — fragile (build hashes in filenames), unsupported
3. Manual JSONL file append — bypasses session manager, risks corruption, misses transcript update events
4. callGateway with sessions.send — triggers a full agent turn, expensive and side-effect heavy

Context

• The internal appendAssistantMessageToSessionTranscript function already exists in src/config/sessions/transcript.ts
• It is used by outbound-send-service.ts and deliver.ts for delivery mirroring
• It handles idempotency, deduplication, and emits transcript update events
• It is already exported from config/sessions/transcript.runtime.ts but not wired into the plugin runtime surface

Environment

• OpenClaw 2026.4.24
• Plugin: openclaw-plugin-cron-context