Add Agents array to CommittedMetadata for multi-agent checkpoints

[peyton-alt]

Note

Introduces multi-agent tracking for committed checkpoints while preserving backwards compatibility.

• Add Agents array to CommittedMetadata; keep Agent as the first agent for compat (single-session omits agents)
• Update writeMetadataJSON to merge multi-session data: deduplicate/merge agents, session_ids, files_touched, and increment session_count
• New mergeAgents helper for order-preserving deduplication
• Add tests: single-session (no agents), multi-session (ordered agents array), and deduplication; plus helper to read metadata from branch

Risk: Low — additive metadata field and merge logic covered by tests; existing reads continue using agent field

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[Copilot]

Pull request overview

This PR adds an Agents array field to CommittedMetadata to support tracking multiple agents in multi-session checkpoints. The implementation maintains full backwards compatibility with existing single-agent checkpoints while enabling proper tracking when multiple AI agents collaborate on the same checkpoint.

Changes:

• Added Agents []string field to CommittedMetadata for tracking all contributing agents in multi-session checkpoints
• Implemented agent merging logic with deduplication while preserving order
• Maintained backwards compatibility by keeping the singular Agent field populated with the first agent

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
cmd/entire/cli/checkpoint/checkpoint.go	Added Agents field to CommittedMetadata struct with appropriate JSON tag and documentation
cmd/entire/cli/checkpoint/committed.go	Implemented agent merging logic in writeMetadataJSON and added mergeAgents helper function
cmd/entire/cli/checkpoint/checkpoint_test.go	Added comprehensive test coverage for single-session (no Agents array), multi-session merge (multiple agents), and same-agent deduplication scenarios

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

The session ID generation using string(rune('0'+i)) is unconventional and could be confusing to readers. While it works correctly for i=1 and i=2 (producing "session-1" and "session-2"), a more idiomatic approach would be using fmt.Sprintf("session-%d", i) or strconv.Itoa(i) for better readability and maintainability.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

The session ID generation is incorrect. string(rune('0'+i)) creates a single-character string from a rune, which for i=1 gives '1' and for i=2 gives '2'. This means the session IDs will be "session-1" and "session-2", but if the loop were to iterate beyond i=9, it would produce non-digit characters. A safer approach would be to use string formatting like fmt.Sprintf("session-%d", i) or strconv.Itoa(i).