PR #73658: fix(agents): drop blank-text ContentBlocks on every Anthropic transcript path (#73640)

• Repository: openclaw/openclaw
• Author: hclsys
• State: closed | merged: False
• Link: https://github.com/openclaw/openclaw/pull/73658

Description (problem / solution / changelog)

What

Fixes #73640. Anthropic's API rejects requests whose messages.N.content.K carries a { type: "text", text: "" } block:

Validation error: The text field in the ContentBlock object at messages.64.content.0 is blank. Add text to the text field, and try again.

Once that 400 fires for a session, every subsequent turn replays the same transcript and hits the same error — the session is wedged with no per-turn recovery path.

Root cause

sanitizeSessionMessagesImages in src/agents/pi-embedded-helpers/images.ts was the only place filtering empty-text blocks before the provider call, but it only did so on a single narrow path: role === "assistant" AND stopReason !== "error" AND sanitizeMode === "full" AND (when preserveSignatures is on) no thinking/redacted_thinking block present.

Empty { type: "text", text: "" } blocks survived for five other branches:

1. role === "user" content arrays — only image sanitization ran, never touched text blocks
2. role === "toolResult" content arrays — same
3. role === "assistant" with stopReason === "error" — bypassed the filter entirely
4. role === "assistant" under sanitizeMode === "images-only" — bypassed the filter
5. role === "assistant" with preserveSignatures AND thinking block — kept original content including blank text

Any one of those five paths could produce a transcript Anthropic rejects.

Fix

Extract the inlined empty-text filter into a small dropEmptyTextBlocks(content) helper at the top of the file, and apply it uniformly to all five sites:

function dropEmptyTextBlocks<T>(content: readonly T[]): T[] {
  return content.filter((block) => {
    if (!block || typeof block !== "object") return true;
    const rec = block as { type?: unknown; text?: unknown };
    if (rec.type !== "text") return true;
    return typeof rec.text === "string" && rec.text.trim().length > 0;
  });
}

The helper only rewrites text blocks; thinking, redacted_thinking, tool_use, tool_result, and image blocks pass through unchanged. The previous isThinkingOrRedactedBlock carve-out (which kept blank-text companions when a thinking block was present under preserveSignatures) is removed because dropping empties never disturbs thinking-block ordering — and it still triggered the 400.

Test changes

• Updated the existing preserves interleaved thinking block order when signatures are preserved regression test (the canary for the preserveSignatures branch). Title now ends … and drops blank-text companions. The test still pins thinking / redacted_thinking ordering; the blank-text companion is now expected to be dropped.
• New test drops blank-text content blocks on user, toolResult, and error-stopped assistant turns (#73640) pinning the four previously-unfiltered branches in one go.

Verified locally

npx oxlint src/agents/pi-embedded-helpers/images.ts
# Found 0 warnings and 0 errors.

npx vitest run \
  src/agents/pi-embedded-helpers.sanitize-session-messages-images.removes-empty-assistant-text-blocks-but-preserves.test.ts \
  src/agents/pi-embedded-runner.sanitize-session-history.policy.test.ts \
  src/agents/pi-embedded-runner.sanitize-session-history.test.ts
# Tests  116 passed (116)

Pre-implement audit

1. Existing-helper check. The empty-text filter shape was already inlined in the working assistant-full-mode branch (images.ts:143-152); the new helper is the natural extraction. isEmptyAssistantMessageContent (same file, line 35) uses an identical predicate and is left in place because it serves a different caller (full-message classifier vs per-block filter). ✅
2. Shared-helper caller check. dropEmptyTextBlocks is module-private. The 5 call sites are all inside sanitizeSessionMessagesImages. No external contract change. ✅
3. Broader-fix rival scan. Zero rival PRs on #73640. ✅

lobster-biscuit: 73640-anthropic-empty-text-content-block

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Changed files

• CHANGELOG.md (modified, +1/-0)
• src/agents/pi-embedded-helpers.sanitize-session-messages-images.removes-empty-assistant-text-blocks-but-preserves.test.ts (modified, +130/-4)
• src/agents/pi-embedded-helpers/images.ts (modified, +69/-24)