fix(api): normalize content field format before sending to provider - #67767
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Bifrost and OpenRouter strictly validate the message content field,
rejecting assistant messages whose content is neither a string nor
an array of Content block dicts with HTTP 400: 'content field is
neither a string nor an array of Content blocks'.
This was triggered when malformed content (e.g., an array of plain
strings like ["thinking", "text"], or dicts missing the 'type'
key) reached the wire via thinking-only prefill continuation or
message merging.
Fix: add content format normalization to sanitize_api_messages(),
the final pre-API chokepoint that already handles empty tool_calls,
orphaned tool results, and duplicate call IDs. Normalizations:
- Array of plain strings -> Content block array
[{'type':'text','text':'...'}, ...]
- Dicts missing 'type' key -> add type='text' fallback
- Non-string, non-list values -> convert to str
- None/null -> pass through unchanged
alt-glitch
added
type/bug
teknium1
reviewed
Jul 25, 2026
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Thanks for targeting strict-provider message validation. The compatibility gap is still actionable: sanitize_api_messages() on current main has no content-shape normalization (agent/agent_runtime_helpers.py:2762-2957).
Problems
- The new pass is not the final request mutation. The main loop calls
_sanitize_api_messages()before_drop_thinking_only_and_merge_users()(agent/conversation_loop.py:1403-1416), so content can still be changed after this normalization. - The diff contains no regression tests. Existing merge coverage only asserts typed-block inputs and outputs (
tests/run_agent/test_thinking_only_sanitizer.py:244-268). - The proposed merge explanation is not reproduced by current code: mixed string/list branches create typed text blocks, while list/list only concatenates its existing operands (
agent/agent_runtime_helpers.py:1352-1369).
Suggested changes
- Normalize after the drop/merge pass in both request paths, or prove later mutations cannot introduce invalid content.
- Add full request-path tests for malformed lists, typeless dicts, scalar/dict values, and valid typed blocks.
Automated hermes-sweeper review.
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| # --- Normalize content field formats ──────────────────────────── | ||
| # Bifrost/OpenRouter reject assistant messages whose `content` is | ||
| # neither a string nor an array of Content block dicts (e.g. an |
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This is not the final content mutation in the main path: _drop_thinking_only_and_merge_users() runs after this sanitizer at agent/conversation_loop.py:1403-1416. Please place the normalization after that pass (and mirror the summary path), or demonstrate that the later pass cannot create an invalid wire shape.
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Problem
Bifrost and OpenRouter strictly validate the message
contentfield, rejecting assistant messages whose content is neither a string nor an array of Content block dicts with HTTP 400:"content field is neither a string nor an array of Content blocks".This is triggered when malformed content reaches the wire via:
drop_thinking_only_and_merge_userscan produce content as an array of plain strings instead of proper Content blocksFix
Add content format normalization to
sanitize_api_messages(), the final pre-API chokepoint that already handles emptytool_calls, orphaned tool results, and duplicate call IDs.["hello", "world"](strings array)[{"type":"text","text":"hello"}, {"type":"text","text":"world"}][{"text":"no type"}](dicts missingtype)[{"type":"text","text":"no type"}]{"weird": "format"}(non-string, non-list)str(..)None/ valid string / valid content blocksTesting
All core normalization paths verified:
type→type="text"fallback added