Fix multi-session attribution summary loss

[peyton-alt]

Fix multi-session attribution summary loss

When multiple agent sessions contribute to the same checkpoint (same base commit), per-session
InitialAttribution data was being lost during condensation — the root CheckpointSummary only reflected
the latest session's attribution, not the aggregate across all sessions.

This PR fixes the problem with three changes:

1. Combined attribution on CheckpointSummary

• Adds a combined_attribution field to CheckpointSummary that holds the summed attribution across all
  sessions in a checkpoint
• After all sessions are condensed in PostCommit, updateCombinedAttributionForCheckpoint reads each
  session's InitialAttribution, aggregates the line counts (agent lines, human added/modified/removed,
  total committed), and writes the result back to the root metadata
• Existing combined_attribution is preserved when the summary is rewritten by subsequent session
  condensations

2. Lightweight ReadSessionMetadata path

• Adds GitStore.ReadSessionMetadata() that reads only metadata.json for a given session index — no
  transcript or prompt blobs
• Used by the aggregation logic to avoid expensive full-content reads when only attribution data is
  needed

3. Diagnostic prompt_attributions persistence

• Persists raw per-prompt attribution diagnostics (PromptAttributions) as JSON in each session's
  metadata.json
• Wired through both v1 and v2 committed checkpoint writers
• Enables root-cause analysis of attribution bugs by showing exactly which prompt recorded which "user"
  lines

Note

Medium Risk
Updates checkpoint metadata schema and post-commit behavior to persist new diagnostic attribution data and to mutate root checkpoint metadata after writes; errors could affect checkpoint history or attribution reporting for existing multi-session checkpoints.

Overview
Fixes multi-session attribution loss by introducing a root-level combined_attribution field on CheckpointSummary and updating it after all sessions are condensed.

Adds a cheap ReadSessionMetadata path plus UpdateCheckpointSummary to recompute/sum per-session initial_attribution and persist the aggregate without rewriting session content; root summary writes now preserve any existing combined_attribution instead of dropping it.

Also persists raw per-prompt attribution diagnostics by JSON-encoding PromptAttributions into session metadata.json (prompt_attributions), and wires this through both v1 and v2 committed checkpoint writers. Includes a regression test covering multi-session combined attribution persistence.

^{Written by Cursor Bugbot for commit 44bde7b. Configure here.}

[Copilot]

Pull request overview

Fixes loss of attribution summary information when a single checkpoint is associated with multiple sessions, and adds diagnostic persistence for prompt-level attribution inputs.

Changes:

• Adds a post-commit step to compute and persist a combined (multi-session) attribution value at the checkpoint root.
• Persists raw per-prompt attribution data into session metadata for debugging attribution issues.
• Preserves any previously-written combined_attribution when rewriting the root checkpoint summary.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
cmd/entire/cli/strategy/manual_commit_hooks.go	Updates PostCommit to compute/store combined attribution for multi-session checkpoints.
cmd/entire/cli/strategy/manual_commit_condensation.go	Serializes prompt attribution details into WriteCommittedOptions for persistence.
cmd/entire/cli/checkpoint/v2_committed.go	Writes prompt_attributions into v2 session committed metadata.
cmd/entire/cli/checkpoint/committed.go	Writes prompt_attributions, preserves combined_attribution in root summary, and adds an update method to patch root metadata after sessions are written.
cmd/entire/cli/checkpoint/checkpoint.go	Extends committed metadata schemas/options with prompt_attributions and root combined_attribution.

[peyton-alt]

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