Filter out empty messages from LLM prompt construction#3967
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Filter out empty messages from LLM prompt construction#3967
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Empty messages (with no content and no tool calls) could be sent to the LLM, which is wasteful and potentially causes issues. This change: - Skips assistant messages with empty body and no tool calls during history construction (matching the existing guard on user messages) - Adds a safety filter (hasMessageContent) on the final messages array to catch any empty messages from any source, while preserving assistant messages with tool calls and tool response messages CS-10116 https://claude.ai/code/session_01JMzG85yR6uQUXVfnUTegXz
- Remove hasMessageContent filter: it was redundant with the inline guards already present for each message type and would silently mask construction bugs rather than surfacing them - Fix test: use correct field name `id` instead of `toolCallId` for encoded command requests (matching all other tests in the file) - Add tool result assertions to verify the assistant+tool message pairing is preserved when assistant body is empty https://claude.ai/code/session_01JMzG85yR6uQUXVfnUTegXz
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@claude iterate to fix the linting and test issues. One of the matrix tests is failing because there is an expect for one attached file that should be checking the count is 2. |
jurgenwerk
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Feb 11, 2026
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Pull request overview
This pull request filters out empty messages from LLM prompt construction to prevent wasteful and potentially problematic API calls. The change modifies the history construction logic to skip assistant messages that have both an empty body and no tool calls, matching the existing filtering behavior for user messages.
Changes:
- Modified
buildPromptForModelto conditionally add assistant messages only when they have content or tool calls - Added comprehensive test coverage for empty message filtering scenarios
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| packages/runtime-common/ai/prompt.ts | Updated assistant message construction to filter out empty messages while preserving messages with tool calls |
| packages/ai-bot/tests/prompt-construction-test.ts | Added three new tests to verify empty message filtering for assistant and user messages |
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Empty messages (with no content and no tool calls) could be sent to the
LLM, which is wasteful and potentially causes issues. This change:
history construction (matching the existing guard on user messages)
to catch any empty messages from any source, while preserving
assistant messages with tool calls and tool response messages
CS-10116
https://claude.ai/code/session_01JMzG85yR6uQUXVfnUTegXz