fix: add timezone conversion support to time tool

[tsubasakong]

Summary

• add explicit IANA timezone support to the builtin time tool
• implement the missing convert and format operations
• support naive timestamps when timezone / from_timezone is supplied, and fall back to JobContext.metadata.user_timezone when available
• add focused tests for explicit timezone handling, context fallback, DST conversion, formatting, and invalid timezone errors

Validation

• git diff --check
• Rust toolchain is not installed on this host, so compile/test validation is deferred to CI

Fixes #662

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly upgrades the time built-in tool by integrating robust timezone awareness. It introduces the ability to convert timestamps between different IANA timezones, format them according to specified timezones and patterns, and intelligently handle naive timestamps by inferring timezone context. These enhancements provide greater flexibility and accuracy for time-related operations within the system.

Highlights

• IANA Timezone Support: Added explicit support for IANA timezone names (e.g., 'America/New_York') across various time operations.
• New Operations: Implemented new convert and format operations to allow direct timezone conversion and custom formatting of timestamps.
• Naive Timestamp Handling: Enabled the tool to interpret naive timestamps (without timezone information) when an explicit timezone or from_timezone is provided, or by falling back to the JobContext.metadata.user_timezone.
• Enhanced Parameter Schema: Updated the tool's parameter schema to include new fields like input, timezone, from_timezone, to_timezone, and format_string, while maintaining backward compatibility for existing timestamp and format parameters.
• Comprehensive Testing: Added focused test cases to validate explicit timezone handling, context fallback mechanisms, Daylight Saving Time (DST) conversions, custom formatting, and proper error handling for invalid timezones.

Changelog

• Cargo.toml
  • Added chrono-tz dependency to enable IANA timezone support.
• src/tools/builtin/time.rs
  • Updated chrono imports and added chrono_tz::Tz for timezone types.
  • Expanded the tool's description to reflect new parsing and formatting capabilities.
  • Modified the parameters_schema to include convert operation, input, timezone, from_timezone, to_timezone, and format_string fields, while retaining timestamp and format for backward compatibility.
  • Refactored the execute function to delegate time operations to new, modular helper functions.
  • Implemented execute_now, execute_parse, execute_convert, execute_format, and execute_diff functions to encapsulate specific time logic.
  • Introduced utility functions such as require_input, resolve_parse_timezone, resolve_timezone_for_output, context_timezone, optional_timezone, parse_timezone, parse_timestamp, parse_naive_datetime, and localize_naive_datetime to manage input parsing and timezone resolution.
  • Added extensive unit tests covering explicit timezone usage, context-based timezone fallback, DST transitions, custom formatting, and error handling for unknown timezones.

Activity

• The author performed git diff --check for local validation.
• Rust toolchain compilation and testing validation are deferred to CI, indicating reliance on automated build and test pipelines.

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[gemini-code-assist]

Code Review

This pull request significantly enhances the time tool by adding comprehensive timezone support, implementing convert and format operations, and including a solid set of tests. The code is well-structured, with the core logic refactored into clear, focused functions. My review focuses on improving the consistency of the JSON output across the different time operations. By standardizing the fields returned, we can make the tool more predictable, easier to maintain for developers who will consume its output, and prevent client-side parsing failures.

[gemini-code-assist]

The output of time operations is inconsistent across different operation values regarding the iso and utc_iso fields. For consistency with the now operation and to support a smoother transition, please return both iso (for backward compatibility) and the more explicit utc_iso field. This ensures a consistent and valid JSON structure, preventing potential client-side parsing failures.

Suggested change

	"iso": dt.to_rfc3339(),
	"iso": dt.to_rfc3339(),
	"utc_iso": dt.to_rfc3339(),

References

1. API endpoints should return a consistent and valid JSON structure to prevent client-side parsing failures and ensure predictability.

[gemini-code-assist]

This new convert operation only returns utc_iso. To maintain consistency with other operations like now and for backward compatibility with consumers that might expect an iso field, please add the iso field here as well, with the same value as utc_iso. This ensures a consistent and valid JSON structure, preventing potential client-side parsing failures.

Suggested change

	"utc_iso": dt.to_rfc3339(),
	"iso": dt.to_rfc3339(),
	"utc_iso": dt.to_rfc3339(),

References

1. API endpoints should return a consistent and valid JSON structure to prevent client-side parsing failures and ensure predictability.

[gemini-code-assist]

Similar to other operations, this should return both iso and utc_iso for consistency. This helps in maintaining a uniform output structure across all time-related operations, ensuring a consistent and valid JSON structure and preventing potential client-side parsing failures.

Suggested change

	result["utc_iso"] = serde_json::Value::String(dt.to_rfc3339());
	result["iso"] = serde_json::Value::String(dt.to_rfc3339());
	result["utc_iso"] = result["iso"].clone();

References

1. API endpoints should return a consistent and valid JSON structure to prevent client-side parsing failures and ensure predictability.