Conversation history missing on resume (except last message)

Description

After upgrading from Claude Code v2.1.15 to v2.1.24+ (and later 2.1.34), some sessions only show the last message when resumed, with all prior conversation history missing. The history is present in the JSONL file but not loaded by Claude Code.

Note: Downgrading back to v2.1.15 does NOT fix the issue, indicating the corruption happened at write time, not at read time.

_Update: I'm still getting this occasionally (so it wasn't version-switch related)_

Symptoms

• Resume a session → only see the last message
• Full conversation history exists in the .jsonl file
• Affects some sessions but not others (no clear version pattern)

Investigation

Had Claude analyze a working session vs. a broken session. Found two corruption issues in the broken session's JSONL file:

1. Snapshot messageId Collision

file-history-snapshot entries have messageId values that collide with the immediately following message's uuid, creating ID ambiguity:

• Line 53: snapshot with messageId: "5c1312fa-..."
• Line 54: user message with uuid: "5c1312fa-..." (same ID!)

2. Broken Parent Chain Reference ⚠️ This is the critical bug

An entry references a parent UUID that doesn't exist in the file, breaking conversation chain traversal:

• Line 50: progress entry with parentUuid: "1b366c02-..."
• No entry in the file has uuid: "1b366c02-..."
• Should point to the previous entry: uuid: "97fdd911-..."

This broken link prevents Claude Code from traversing the conversation history backwards when loading the session. When traced back from the last message, the chain stops at this broken reference after only 6 entries instead of going back through all 26 entries in the conversation.

Root Cause

Unknown what causes the corruption during writing. Possibly related to:

• Sessions being open during version upgrade
• Specific timing/race conditions
• Not all sessions affected (sporadic issue)

Workaround

Created a Nushell script that detects and fixes both issues:

• Sets snapshot messageId to null (removes collision)
• Fixes broken parent references to point to correct preceding entries
• Creates timestamped backups (non-destructive)

Fix script: https://gist.github.com/tennox/90ef5c803ec4b64c9fbba0f71ca1ae2e

nu fix-cc-session.nu ~/.config/claude/projects/YOUR-PROJECT/SESSION-ID.jsonl

Environment

• Upgraded from: v2.1.15
• Upgraded to: v2.1.24, then v2.1.34
• OS: Linux (NixOS)
• Pattern: Some sessions affected, others not (no clear correlation with version)

Expected Behavior

Resuming a session should load the full conversation history, regardless of which version created the session.

Actual Behavior

Only the last message is displayed; all prior history is invisible despite being present in the JSONL file.