PR #75339: fix(agents): normalize structured delta.content blocks to prevent [object Object] in chat replies

• Repository: openclaw/openclaw
• Author: lonexreb
• State: open | merged: False
• Link: https://github.com/openclaw/openclaw/pull/75339

Description (problem / solution / changelog)

Bug being fixed

Closes #75268. Same family of bug as the closed #70806.

Mistral with native reasoning enabled returns OpenAI-compatible streaming delta.content as an array of typed blocks instead of a flat string (per Mistral native reasoning docs):

{"delta": {"content": [
  {"type": "thinking", "thinking": "Let me think..."},
  {"type": "text", "text": "Here is the answer."}
]}}

The transport loop at src/agents/openai-transport-stream.ts treated delta.content as a string unconditionally:

if (choice.delta.content) {
  appendTextDelta(choice.delta.content);  // gets an array, downstream concat → "[object Object]"
}

So the array fell through to appendTextDelta and downstream string concatenation produced "[object Object]" repeating once per block in user-visible chat replies. The corruption then propagated into session transcript files and memory, matching the reporter's symptoms exactly.

Fix

Add normalizeStructuredContentDelta() that handles the three observed shapes:

Block types thinking / reasoning / reasoning.text route to thinking deltas; anything else with a text/content/thinking string field routes to text deltas. Unrecognized objects with no string-valued field produce zero parts (no [object Object] leak).

Reused the same normalizer in the reasoning_content / reasoning / reasoning_text fallback inside getCompletionsReasoningDeltas, so non-string payloads in those fields also stop collapsing to [object Object].

Why this is the best fix

• Right layer: the OpenAI-compatible transport is shared across all OpenAI-compatible providers, not just Mistral. The fix protects every provider that ever ships structured delta blocks (including future ones), without provider-specific compat flags.
• Defensive by design: any object/array that doesn't yield string text is dropped silently rather than coerced. The regression test explicitly asserts [object Object] never appears in normalized parts even for unrecognized object shapes.
• Backwards compatible: the existing string fast path is unchanged; existing 96 tests in the same file still pass.
• Complements PR #67203: that PR (currently open) tried to extend getCompletionsReasoningDeltas to handle arrays, but it doesn't touch delta.content itself, which is the actual user-visible leak path described in #75268. This PR covers both delta.content and the reasoning_content/reasoning/reasoning_text family with one shared helper.

Test plan

• pnpm test src/agents/openai-transport-stream.test.ts — 103/103 pass (7 new + 96 existing)
• pnpm tsgo:core — clean
• pnpm tsgo:core:test — clean
• pnpm exec oxfmt --check — clean
• 7 new regression cases cover: plain string, empty/null/undefined, mixed array, reasoning + reasoning.text block types, untyped block with content field, unrecognized objects (explicit [object Object] non-leak assertion), and skipped empty/non-string text fields.

https://github.com/openclaw/openclaw/issues/75268

Changed files

• CHANGELOG.md (modified, +1/-0)
• src/agents/openai-transport-stream.test.ts (modified, +112/-0)
• src/agents/openai-transport-stream.ts (modified, +119/-6)