openclaw - 💡(How to fix) Fix [Bug]: Control UI webchat re-sends image messages 4–9× causing 413 overflow and permanent session freeze [1 participants]

Summary

When pasting/uploading an image in the Control UI (webchat), the frontend repeatedly re-sends the same message (containing ~2MB base64 image data) 4–9 times. Each duplicate is persisted into the session JSONL, quickly exceeding the provider's request body limit (HTTP 413). Auto-compaction cannot shrink base64 image data, so the session enters a fatal compaction loop and becomes permanently unresponsive.

Steps to reproduce

1. Open Control UI webchat (localhost:19000)
2. Start a conversation (a few exchanges to build some context)
3. Paste a screenshot (Cmd+V) — typical PNG ~1.5–2MB
4. Send the message

Expected behavior

• The image message is sent once
• Gateway resizes the image if needed and forwards to the model
• Session continues normally

Actual behavior

• The webchat frontend sends the same message 4–9 times within seconds (observed timestamps show ~5s intervals)
• Each message carries the full base64-encoded image (~2.2MB per message in session JSONL)
• The session file grows to 8–9MB from just one user action
• Provider returns 413 Failed to buffer the request body: length limit exceeded
• Gateway attempts auto-compaction 3 times, all fail (base64 data is incompressible)
• Gateway then attempts tool-result truncation, also fails
• Session is permanently stuck — no further messages can be processed

Evidence from logs

Gateway error log (two separate incidents, same session day):

Incident 1 — 12:17 (9 duplicates):

2026-04-24T12:17:08.578+08:00 [agent/embedded] [context-overflow-diag] sessionKey=agent:main:main messages=68 error=413 Failed to buffer the request body: length limit exceeded
2026-04-24T12:17:08.578+08:00 [agent/embedded] context overflow detected (attempt 1/3); attempting auto-compaction
... (attempts 2/3, 3/3 all fail with same 413)
2026-04-24T12:17:24.859+08:00 [agent/embedded] [context-overflow-recovery] Attempting tool result truncation (contextWindow=1000000 tokens)
2026-04-24T12:17:26.311+08:00 ... still 413

Incident 2 — 13:28 (4 duplicates, fresh session after /new):

2026-04-24T13:28:54.720+08:00 [agent/embedded] ... messages=17 error=413 Failed to buffer the request body: length limit exceeded
... (same compaction loop, same outcome)

Session JSONL analysis (Incident 2):

• Session file total: 8.7MB (70 lines, only 17 messages before the image)
• Image data per message: 2,238,656 chars base64 (~1,639 KB decoded PNG)

Root cause analysis

Two issues combine to create the crash:

1. Frontend duplicate submission (primary bug)

The webchat frontend re-sends the same image message multiple times. Possible causes:

• No client-side message deduplication (idempotency key)
• Retry logic triggered by the backend failing to respond (413 → timeout → retry with same payload)
• No backoff or max-retry limit for large payloads

2. No server-side dedup or size guard (secondary)

• Gateway accepts and persists each duplicate into the session JSONL without deduplication
• No per-message size limit or image pre-processing before session injection
• Compaction cannot reduce base64 image data, making recovery impossible once oversized

Suggested fixes

1. Client-side dedup: Assign a unique message ID on send; reject re-sends of the same ID
2. Don't retry 413: HTTP 413 is a permanent error — retrying with the same payload will always fail
3. Server-side dedup: Gateway should reject messages with duplicate content/timestamp within a short window
4. Image size guard: Resize/compress images before injecting base64 into the session (the [agents/tool-images] Image resized pipeline exists but doesn't apply to webchat inbound images)
5. Compaction awareness: When compaction fails and the oversized content is image data, consider dropping image content blocks from older messages rather than failing the entire session

Environment

• OpenClaw: 2026.4.22 (00bd2cf)
• OS: macOS 15.7.6 (Darwin arm64, Apple Silicon)
• Node.js: v22.17.0
• Install method: npm (global)
• Channel/UI: Control UI webchat (localhost)
• Model: claude-opus-4-6 via IdeaLab proxy
• Browser: Chrome (Chromium-based)

Workaround

• Avoid pasting large images directly in webchat
• Instead, save images to disk and tell the agent to read them via the read or image tool
• Or compress images to <500KB before pasting

Related issues

• #3477 — Webchat image paste causes sequence gap error (different symptom, possibly related frontend code path)
• #49328 — Control UI duplicate messages on AI reply (duplicate direction is reversed but may share retry logic)
• #53271 — Webchat images not uploaded (opposite problem — images lost vs duplicated)
• #69448 — Agent runner retries full turns on tool errors (server-side duplication, different layer)