VS Code sessions spontaneously split, swap, and duplicate between panels

Bug Report — High Priority

Problem

Claude Code sessions in VS Code are spontaneously splitting and swapping between open panels without user action. This results in:

1. Session splitting — A single session suddenly appears in two different VS Code Claude panels
2. Session swapping — A panel that was connected to session A suddenly starts showing session B
3. Ghost sessions — New session files appear in ~/.claude/projects/ that the user never created
4. Session duplication — Multiple Claude binary processes attach to the same session ID (confirmed via ps aux | grep resume)

Impact

• Users lose track of which panel is connected to which session
• Work in progress vanishes when a panel swaps to a different session
• Multiple processes writing to the same JSONL file causes data corruption and crashes
• Combined with the "Prompt is too long" bug (#25274), this makes Claude Code nearly unusable for multi-session workflows

Evidence from a single user session (Feb 12, 2026)

Duplicate processes on same session:

PID 71397 --resume c615748f (started 9:55 PM, active)
PID 78674 --resume c615748f (started 11:07 PM, zombie)
PID 81142 --resume c615748f (started 11:21 PM, zombie)

Three processes all attached to the same session file, spawned at different times without user action.

Ghost sessions: User had 4 active sessions. After a short period, 5 additional session files appeared that the user did not create. Several contained only the <ide_opened_file> system reminder — suggesting the extension spawned new sessions when broadcasting file-open events.

Session swapping: User's Infrastructure session (actively editing MD files) vanished from its panel. The work appeared in a different session file with a different first message ("Finder + Client Modules"), suggesting the panel swapped mid-conversation.

Environment

• Claude Code v2.1.39 (VS Code extension, macOS)
• VS Code with 4-5 Claude panels open simultaneously
• macOS Darwin 25.2.0

Severity

High — This makes multi-session workflows (the primary use case for VS Code panels) unreliable. Users cannot trust that their panel is connected to the correct session, and work disappears without warning.

Related

• #25274 (tool results embed full file content)
• #24709 (session ID not visible in tab titles)