Rewind history lost after compaction in sessions with many rewinds (branching tree)

[harshidwasekar]

Bug Description

Rewind history is completely lost after automatic compaction in sessions that have extensive rewind usage (branching conversation tree). After compaction, only ~2 messages are visible in rewind despite the session containing a large multi-day conversation.

Environment

• Claude Code version: 2.1.34
• OS: macOS (Darwin 25.2.0)

Steps to Reproduce

1. Start a long Claude Code session
2. Use rewind frequently throughout the session (creating a non-linear conversation tree)
3. Continue working until automatic compaction (context limit) is triggered
4. After compaction, attempt to rewind — only post-compaction messages are visible

Analysis

I analyzed the session JSONL file and found the following:

Tree structure:

• Total nodes in tree: 10,671
• Main path (root to latest message): 64 messages (all post-compaction)
• Nodes on dead branches (from rewinds): 10,607
• Branch points (rewinds): 275 (max 6 children at a single branch point)
• 3 separate root nodes exist in the tree

The bug — isSidechain never set:

• Off-path user/assistant messages with isSidechain=False: 2,303
• Off-path user/assistant messages with isSidechain=True: 0

When rewinding during the session, abandoned branches were never marked as isSidechain=True. All messages in the entire tree have isSidechain=False.

When compaction occurred, it created a new root node (system message with conversation summary) with parentUuid=None. The main path now traces from this new root forward — completely disconnected from the pre-compaction tree. The original conversation (rooted at 2 earlier root nodes) is intact in the JSONL but unreachable via rewind navigation, which follows parentUuid links backward from the current leaf.

Timeline:

• Day 1 — Original session root (conversation begins)
• Day 1 through Day 3 — Extensive work with many rewinds creating 275 branch points
• Day 3 — Compaction creates new root node with summary, severing the tree
• Day 3+ — Only 64 messages on the new main path, rewind shows ~2 messages

Expected Behavior

Rewind should be able to navigate back through the pre-compaction conversation history, as it does in sessions without heavy rewind usage.

Actual Behavior

Rewind only shows messages after compaction. The entire pre-compaction conversation (spanning 2+ days of work) is inaccessible via rewind.

Possible Root Causes

1. isSidechain not being set on rewind: When the user rewinds, the abandoned branch messages should be marked isSidechain=True but this never happens (0 out of 10,671 nodes have this flag set to True)
2. Compaction disconnects the tree: The new summary root node has parentUuid=None instead of linking back into the pre-compaction tree, making the old tree unreachable via parent traversal

Workaround

The full conversation is preserved in the session JSONL file and can be read directly, but it's not navigable through the rewind UI.

This report was generated by Claude Code

[github-actions]

Found 3 possible duplicate issues:

1. [BUG] Conversation compaction loses entire history, ctrl+e unresponsive #19888
2. [BUG] Conversation chain breaks mid-session - earlier messages lost on resume #21617
3. [Bug] /rewind creates in-file branches not visible in resume picker, contrary to documentation #19451

This issue will be automatically closed as a duplicate in 3 days.

• If your issue is a duplicate, please close it and 👍 the existing issue instead
• To prevent auto-closure, add a comment or 👎 this comment

🤖 Generated with Claude Code

[scapeshift-ojones]

Your analysis of isSidechain never being set and compaction severing the tree via parentUuid=None was instrumental. I've confirmed the same findings independently on v2.1.47 — branch data is perfectly preserved in JSONL (correct parentUuid linkage, multi-child nodes) but the UI provides no way to navigate it. Right-arrow in the /resume picker does nothing.

Consolidated into #27242 alongside post-compaction history loss and a new post-plan-mode context loss scenario. All three share the same root cause: data is preserved in JSONL but the TUI has no viewer for it.

If this has been blocking your workflow, please 👍 and comment on #27242 — consolidated issues need engagement to reach the triage threshold.