[gpt-oss] Add Tool/ConversationContext classes and harmony_utils

[WoosukKwon]

This PR does not include MCP yet. cc @heheda12345

[gemini-code-assist]

Code Review

This pull request introduces new classes for managing conversation context and tools, along with utility functions. The changes are generally well-structured, but there are a few areas that need attention. I've identified a critical bug that could cause a crash, along with several high-severity issues related to code duplication and non-deterministic behavior that impact maintainability and testability. Addressing these points will improve the robustness and quality of the new components.

[gemini-code-assist]

The while loop condition rendered_tokens[last_n] != self.last_tok is unsafe and can lead to an IndexError if self.last_tok is not present in rendered_tokens. This can occur if append_output hasn't been called, leaving self.last_tok as None, or if token generation logic changes. The loop needs a boundary check to prevent it from accessing an invalid index.

        if self.last_tok is not None:
            try:
                # Find the index of the last token from the end.
                last_tok_r_idx = rendered_tokens[::-1].index(self.last_tok)
                last_tok_idx = len(rendered_tokens) - 1 - last_tok_r_idx
                # Process tokens that appear after the last_tok
                for tok in rendered_tokens[last_tok_idx + 1:]:
                    self.parser.process(tok)
            except ValueError:
                # self.last_tok not found in rendered_tokens.
                # The original code would crash.
                pass

[WoosukKwon]

cc @simon-mo

[gemini-code-assist]

Using datetime.datetime.now() for a default start_date introduces non-determinism, which can make testing difficult and lead to flaky tests. It's better to use a fixed default date to ensure deterministic behavior, or require the caller to provide the date explicitly.

Suggested change

	if start_date is None:
	start_date = datetime.datetime.now().strftime("%Y-%m-%d")
	if start_date is None:
	start_date = "2024-01-01"

[WoosukKwon]

Good point. I think this is something we should remember and be careful about. No immediate fix though.

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