fix: show available sessions for invalid --resume identifiers

[sonwr]

When gemini --resume <id> receives an invalid identifier, the CLI already has the matching project sessions in memory but only tells the user to run --list-sessions.

This change includes a compact list of available sessions directly in the error output so the user can immediately retry with a valid index or UUID.

What changed

• pass available sessions into the invalid resume SessionError
• include a compact session summary in the error message
• limit inline output to 10 sessions and point users to --list-sessions for the full list
• add tests for inline session summaries and truncation behavior

Testing

• npx vitest run packages/cli/src/utils/sessionUtils.test.ts packages/cli/src/gemini.test.tsx

Fixes #21764

[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 improves the user experience of the gemini CLI tool by providing immediate, actionable feedback when an invalid session identifier is used with the --resume command. Instead of simply stating the identifier is invalid and suggesting --list-sessions, the error message now directly presents a concise list of available sessions, allowing users to quickly correct their input without an extra step.

Highlights

• Enhanced Error Messaging: The gemini --resume command now provides a compact list of available sessions directly within the error message when an invalid session identifier is used, improving user guidance.
• Session List Truncation: Implemented logic to limit the inline display of available sessions to a maximum of 10, with a clear prompt to use --list-sessions for the complete list.
• New Utility Function: A new helper function, formatAvailableSessions, was added to format and manage the display of session summaries within error messages.
• Comprehensive Testing: New unit tests were introduced to verify the correct behavior of the enhanced error messages, including the display of session summaries and the truncation mechanism.

Changelog

• packages/cli/src/utils/sessionUtils.test.ts
  • Added a second session to existing test data to verify multiple sessions are displayed.
  • Updated the invalid-uuid test to assert the presence of the new session summary in the error message.
  • Introduced a new test case to specifically verify the truncation logic for displaying a limited number of sessions.
• packages/cli/src/utils/sessionUtils.ts
  • Modified the SessionError.invalidSessionIdentifier static method to accept an optional sessions array.
  • Updated the error message construction to dynamically include a formatted list of available sessions if provided.
  • Introduced MAX_SESSIONS_IN_INVALID_RESUME_MESSAGE constant to define the display limit.
  • Added a new private helper function formatAvailableSessions to generate the compact session summary string, including truncation logic.
  • Updated the SessionSelector.resolveSession method to pass the sortedSessions to the invalidSessionIdentifier error.

Activity

• No specific activity (comments, reviews, or progress updates) has been recorded for this pull request yet.

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[gemini-code-assist]

Code Review

This pull request introduces a helpful usability improvement by showing available sessions on an invalid --resume identifier. The implementation is clean and well-tested. I've identified a minor bug where the error message can show duplicated text when the session list is truncated, and I've provided suggestions to fix this in both the implementation and the corresponding test.

[gemini-code-assist]

This line introduces a small bug where the error message can contain duplicated text. The phrase Run --list-sessions to see the full list. is added here, but it's also part of the main error message template in invalidSessionIdentifier. When the session list is truncated, the user will see this instruction twice.

To fix this, this line should only mention the count of remaining sessions. The instruction to run --list-sessions will still be present once in the final error message.

Suggested change

	` ...and ${sessions.length - visibleSessions.length} more. Run --list-sessions to see the full list.`,
	` ...and ${sessions.length - visibleSessions.length} more.`,

References

1. Avoid displaying verbose validation descriptions directly to the user if they contain concatenated links or other unnecessary information. Instead, use a concise, generic message. This comment addresses duplicated text in an error message, making it more concise.

[gemini-code-assist]

Following the suggested change to avoid duplicated text in the error message, this test assertion should be updated. Instead of checking for the combined sentence, it's better to check for the truncation message (...and 2 more.) and the general instruction (Run --list-sessions...) separately to ensure both are present and the output is correct.

Suggested change

	expect((error as SessionError).message).toContain(
	'...and 2 more. Run --list-sessions to see the full list.',
	);
	expect((error as SessionError).message).toContain('...and 2 more.');
	expect((error as SessionError).message).toContain(
	'Run --list-sessions to see the full list.',
	);

References

1. Avoid displaying verbose validation descriptions directly to the user if they contain concatenated links or other unnecessary information. Instead, use a concise, generic message. This test change reflects the application of this rule to the error message.

[jackwotherspoon]

Going to close this. The author of the original issue has a PR and they are the one assigned to the issue.

Will work on accepting their PR 👍