[BUG] VSCode: "Fork conversation" aborts ALL running agents in the window instead of creating a fork

Summary

In the Claude Code VS Code extension, clicking "Fork conversation" (right-click a message → Fork) no longer creates a new forked conversation. Instead it aborts/stops ALL currently running agents in the VS Code window.

Example: I have 4 agents actively working in 4 separate chat tabs. I right-click any message in any chat and choose Fork conversation → all 4 running agents stop immediately. The expected behavior (a new forked conversation, leaving the others untouched) does not happen.

This is a regression — fork used to correctly open a new conversation without touching sibling sessions. It started ~5–7 days ago for me, which correlates with the extension auto-updating into the 2.1.178+ range (see Timeline below).

Steps to reproduce

1. In VS Code with the Claude Code extension, open multiple chat tabs/panes.
2. Start an agent running in each (so 3–4 sessions are actively generating).
3. Right-click on any message in any conversation → Fork conversation.
4. Observe.

Expected behavior

A new forked conversation is created from that message. Other running agents/sessions in the window are unaffected and keep running.

Actual behavior

No fork is created. Every running agent in the VS Code window is stopped/aborted — as if a global interrupt/abort signal were broadcast to all sessions instead of being scoped to the one conversation being forked.

Impact

Losing all parallel agents' in-flight work with a single mis-click is severe for multi-session workflows (several agents working in parallel across chats). It makes Fork effectively unusable while any agent is running.

Environment

• Claude Code VS Code extension (active): 2.1.185 (/home/<user>/.vscode/extensions/anthropic.claude-code-2.1.185-linux-x64)
• Also present: 2.1.183 (.vscode-server), 2.1.178 (.vscode-server)
• Claude CLI (claude --version): 2.1.175 ← note: CLI is behind the extension
• VS Code: 1.125.1 (x64)
• OS: Ubuntu 24.04.4 LTS, Linux kernel 6.17.0-35-generic, x86_64
• Setup uses both ~/.vscode/extensions and ~/.vscode-server/extensions (local + remote-server extension hosts).

Timeline (extension install dates, correlating with onset ~5–7 days ago)

| Version | Installed | Location |
| --- | --- | --- |
| 2.1.178 | 2026-06-16 | .vscode-server |
| 2.1.183 | 2026-06-19 | .vscode-server |
| 2.1.185 | 2026-06-21 | .vscode (active) |

Onset (~June 16–17) lines up with the jump into the 2.1.178 line.

Possibly related issues

• #33434 — pressing Escape kills all parallel subagents at once (same "shared abort broadcast" symptom).
• #64651 — fork-mode changes altered background-session handling / cross-session behavior.
• #33949 — ESC cannot fully cancel / cancellation scope issues.

These suggest a shared abort/cancellation signal that is not scoped to a single session, which would explain why Fork (which likely issues an interrupt on the source session) is taking down every session in the window.

Suspected root cause

The Fork action appears to dispatch an abort/interrupt that is broadcast to all sessions in the window rather than being scoped to the single conversation being forked. Scoping the abort (or not issuing one at all on fork) to only the source/new session should fix it.