/rewind says "conversation will be forked" but never creates a resumable fork

[chrisvaillancourt]

Bug Description

/rewind promises "The conversation will be forked" but mutates the session in place. After rewinding, the original session disappears from /resume and claude --resume. No fork is created.

CLI text shown at rewind time

  Rewind

  Confirm you want to restore to the point before you sent this message:

  │ did you save the transcript anywhere? if not get it again and put it
  │ in the inbox next to the report but don't commit it.
  │ (9m ago)

  The conversation will be forked.
  The code will be unchanged.

"The conversation will be forked" promises two things:

1. The rewound conversation gets a new session ID
2. The original session stays unchanged and resumable

The docs make the same promise for --fork-session:

This creates a new session ID while preserving the conversation history up to that point. The original session remains unchanged.

— How Claude Code works → Resume or fork sessions

/rewind honors neither.

What actually happens

1. /rewind resets the branch pointer to an earlier message within the same JSONL file
2. No new session file or session ID is created
3. The original end-state vanishes from /resume and claude --resume
4. Post-rewind messages remain in the JSONL (append-only) but no UI can reach them

JSONL evidence

Session 08bbfa97-c2f2-4220-a4a4-d9ca2f10fe42:

• 204 lines, every one marked isSidechain: false — zero isSidechain: true entries
• Every message carries the same sessionId; no second session ID exists
• last-prompt / leafUuid entries advance through messages but never branch into a separate session
• No other JSONL file in the project directory references this session ID

A real fork would produce one of:

• A new JSONL file with a new session ID (containing the rewound conversation), or
• The abandoned branch marked isSidechain: true, with new messages appended as isSidechain: false

Neither occurred.

Expected behavior

When /rewind says "The conversation will be forked":

1. Create a new session with a new session ID for the rewound conversation
2. Leave the original session unchanged and visible in /resume
3. Make both independently resumable

Environment

• Claude Code version: 2.1.126
• OS: macOS 26.4.1 (Darwin, arm64)
• Platform: CLI

Related issues

• Rewind history lost after compaction in sessions with many rewinds (branching tree) #24471 — isSidechain never set on rewound branches; compaction severs the tree. Same root cause, different symptom: that issue covers the rewind picker losing history; this one covers the original session vanishing from /resume.
• [FEATURE] Add option to rewind conversation without creating a fork #9279 (closed) — Requests rewind without forking. Its description confirms rewind is designed to fork every time, making the current behavior a bug.
• Rewind + "Summarize from here" drops pre-rewind messages instead of preserving them #47987 — "Summarize from here" after rewind drops pre-rewind messages. Same class of data loss, different trigger.

[github-actions]

Found 3 possible duplicate issues:

1. Rewind history lost after compaction in sessions with many rewinds (branching tree) #24471
2. Agent sub-sessions pollute /resume picker — isSidechain never set to true #35800
3. [FIX] Rewind picker shows no pre-compact messages for sessions > 5 MB #44772

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

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🤖 Generated with Claude Code

[chrisvaillancourt]

Not a duplicate. Each linked issue describes a different problem:

• Rewind history lost after compaction in sessions with many rewinds (branching tree) #24471 — Rewind picker loses history after compaction severs a large branching tree (10,671 nodes, 275 branch points, 3 root nodes). My session: 155 nodes, 1 root, no compaction.
• Agent sub-sessions pollute /resume picker — isSidechain never set to true #35800 — Agent sub-sessions pollute /resume because isSidechain is never set on them. My session is a single user session with no sub-agents.
• [FIX] Rewind picker shows no pre-compact messages for sessions > 5 MB #44772 — Rewind picker drops pre-compact messages in sessions > 5 MB (SKIP_PRECOMPACT_THRESHOLD). My session is 878 KB, never compacted.

All four issues share a root cause — isSidechain is never set to true — but each manifests differently. This one: /rewind promises "The conversation will be forked" but creates no fork. The original session vanishes from /resume.

DAG analysis

The JSONL is append-only, so the full history survives and can be audited:

Total DAG nodes:   155
Root nodes:        1 (no compaction)
File size:         878 KB (well under #44772's 5 MB threshold)
Branch points:     5 (parentUuid with 2+ children)
isSidechain=true:  0 out of 155

The rewind branched at node 2427ae57 (a system message):

                        2427ae57 (system, ts=14:34:36Z)
                           │
              ┌────────────┴────────────┐
              │                         │
     3b9ed7b5 (user, 14:34:48Z)   e3de1c04 (user, 15:07:58Z)
     [user message A]              [user message B — the rewind target]
              │                         │
         133 descendants            12 descendants
     (main path — leaf here)     (orphaned — no path from leaf)

Both children: isSidechain: false. The final leafUuid (d707f738) sits on the left branch. The right branch — 13 messages — is orphaned: no leafUuid points to it, no UI can reach it, and no separate session file exists for it.

What sets this apart

	#24471	#35800	#44772	This issue
Trigger	Many rewinds + compaction	Agent sub-sessions	Session > 5 MB + compaction	Single /rewind
Symptom	Picker loses history	/resume polluted	Picker drops pre-compact messages	Original session gone from /resume
Compaction?	Yes (3 root nodes)	No	Yes (SKIP_PRECOMPACT_THRESHOLD)	No (1 root, 878 KB)
Core claim	Picker can't navigate branching tree	isSidechain not set on agents	readTranscriptForLoad truncates	CLI says "forked" but no fork exists

The docs say: "This creates a new session ID while preserving the conversation history up to that point. The original session remains unchanged." The /rewind UI says "The conversation will be forked." Neither happened.

[arnfaldur]

Just learned about this the hard way. Very frustrating bug.

[shaunhegarty]

Also just experienced this. Used it specifically because it promised to retain the conversation and now an long and expensive context is lost

[m13v]

the thing that bit me with rewind is that fork and rewind are wired to the same branch-pointer move, so 'forked' really just means resetting the leaf inside the same JSONL. a real fork needs a second session id and a second file, otherwise an append-only log can only ever represent one live branch and the old end-state drops off /resume the second you rewind. once i started treating every fork as its own session file from the start, restart and resume stopped stepping on each other. the single-sessionId-per-file assumption is the whole bug.