feat(cli): add JSON output support for list-sessions#24690

[Khalodddd]

Summary

This PR resolves #24690 by adding support for the --output-format json flag to the list-sessions command. Previously, the command would only output human-readable text, regardless of the format flag, making it difficult to use session data in automated scripts or third-party integrations.

Problem

The listSessions function was previously hardcoded for string-based terminal output only. Additionally, the generateSummary function was called unconditionally, which often produced background logs (e.g., "Generating summary...") that would corrupt the JSON output if a user tried to pipe the data to another tool like jq.

Details

• JSON Support: Modified packages/cli/src/utils/sessions.ts to detect OutputFormat.JSON from the config.
• Output Cleanliness: Wrapped the generateSummary call in a conditional check. It is now skipped when JSON is requested, ensuring a clean data stream to stdout.
• Refactoring: Extracted the sorting logic into a sortedSessions constant. This ensures that the order of sessions (sorted by startTime) is identical in both text and JSON modes.
• Formatting: Used JSON.stringify(sortedSessions, null, 2) for standardized, pretty-printed JSON.

Related Issues

Fixes #24690

How to Validate

1. Build the bundle:

   npm run bundle

2. Test command:

   node .\bundle\gemini.js --list-sessions --output-format json

See attached Image for validation

[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 enhances the list-sessions command by introducing JSON output support, enabling better integration with external tools and scripts. It ensures that the output remains clean by conditionally suppressing auxiliary summary logs when JSON mode is active and standardizes the session sorting logic for consistency.

Highlights

• JSON Output Support: Added support for the --output-format json flag to the list-sessions command to facilitate automated data processing.
• Output Cleanliness: Wrapped the generateSummary call in a conditional check to prevent background logs from polluting the JSON output.
• Refactoring: Extracted session sorting logic into a constant to ensure consistent ordering across both text and JSON output formats.

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[gemini-code-assist]

Code Review

This pull request introduces JSON output support for the listSessions command and prevents summary generation when JSON is requested. The review feedback identifies a redundant sorting operation that can be removed and suggests using grapheme-aware string truncation to avoid issues with multi-byte Unicode characters in the terminal output.

[gemini-code-assist]

The SessionSelector.listSessions() method already returns an array of sessions sorted by startTime (ascending), as implemented in the underlying getSessionFiles utility. Re-sorting the array here is redundant and adds unnecessary complexity. You can simply use the sessions array directly.

  const sortedSessions = sessions;