[Follow-up] Preserve empty tool completion turns in OpenAI prompt normalization

[CJackHwang]

Motivation

• A recent normalization change dropped tool/function messages when their normalized content was empty, which removes the signal that a tool call completed and can trigger repeated tool calls or missing final answers.

Description

• Restore preservation of tool/function turns in normalizeOpenAIMessagesForPrompt by emitting a "null" placeholder when normalizeOpenAIContentForPrompt returns an empty string for those roles instead of skipping the message.
• Keep tool/function messages mapped to the user role as before so tool results remain part of the prompt stream.
• Add a regression unit test TestNormalizeOpenAIMessagesForPrompt_EmptyToolContentPreservedAsNull in internal/adapter/openai/message_normalize_test.go that verifies empty tool output is preserved as the "null" placeholder.

Testing

• Ran go test ./internal/adapter/openai and the package tests passed (ok).

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Codex Task

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Project	Deployment	Actions	Updated (UTC)
ds2api	Ready	Preview, Comment	Mar 21, 2026 5:19pm