openclaw - 💡(How to fix) Fix Heartbeat transcript writes empty user messages, breaks AWS Bedrock [1 comments, 2 participants]

Summary

Commit 58a31b12f7 ("fix(agents): keep runtime wakeups out of chat transcript", merged 2026-04-26) introduced a regression where heartbeat runs write empty user messages ({"role":"user","content":[{"type":"text","text":""}]}) into the session transcript. AWS Bedrock rejects these with:

The text field in the ContentBlock object at messages.X.content.0 is blank.
Add text to the text field, and try again.

This accumulates over time (one per heartbeat cycle, ~every 30 minutes) and eventually causes the Bedrock API call to fail when the empty message falls within the context window.

Root Cause

In src/auto-reply/reply/get-reply-run.ts line 501-505:

const transcriptBodyBase = isHeartbeat
    ? ""                    // <-- Bug: empty string gets persisted as user message
    : hasUserBody
      ? baseBodyFinal
      : "[User sent media without caption]";

Before this commit, transcriptBodyBase was always non-empty (either the actual body text or a placeholder). The intent of the change was to keep heartbeat prompts out of the visible transcript, but the empty string still flows through to transcriptCommandBody → transcriptPrompt, which gets persisted as a user message with content: [{ type: "text", text: "" }].

The Bedrock provider (amazon-bedrock.js) has empty-text guards for assistant messages but not for user messages or toolResult messages, so the empty content passes through to the API.

Steps to Reproduce

1. Configure an AWS Bedrock model (e.g., amazon-bedrock/global.anthropic.claude-opus-4-6-v1)
2. Enable heartbeats (default 30-minute interval)
3. Wait for several heartbeat cycles
4. Send a message — eventually Bedrock rejects with the blank text error

Evidence

Session transcript analysis shows 11 empty user messages, all at exact 30-minute intervals matching heartbeat timing:

2026-04-27 00:31:54 UTC  {"role":"user","content":[{"type":"text","text":""}]}
2026-04-27 01:00:12 UTC  (same)
2026-04-27 01:30:12 UTC  (same)
...every 30 mins...
2026-04-27 05:01:51 UTC  (same)

Suggested Fix

Two complementary fixes:

1. Root cause (get-reply-run.ts)

When isHeartbeat is true and transcriptBodyBase is empty, either:

• Skip persisting the user message to the transcript entirely, or
• Use a non-empty placeholder like "[heartbeat]" that gets filtered by the existing heartbeat pair filter

2. Defensive (amazon-bedrock.js in pi-ai)

Add the same empty-text guard that exists for assistant messages to user messages and toolResult messages:

// In convertMessages, user case:
if (typeof m.content === "string") {
    const sanitized = sanitizeSurrogates(m.content);
    if (sanitized.trim().length === 0) continue; // Skip empty user messages
    ...
}

Environment

• OpenClaw version: 2026.4.26
• OS: macOS (Darwin 25.4.0 arm64)
• Provider: AWS Bedrock (Claude Opus 4.6)
• Regression introduced in: commit 58a31b12f7 (2026-04-26)
• Last working version: 2026.4.11

Related

• #30117 (closed as not planned — same symptom, different root cause)