IDE extension hangs indefinitely when the workspace contains more than one folder (multi-root)

Summary

In a multi-root workspace, a new Claude Code session in the IDE never responds.
The UI shows a spinner indefinitely, the stop/interrupt button is unresponsive, and
the only way to regain control is to close the session. The same two folders work
correctly with the standalone CLI at the identical version, so the defect appears to
be in the extension's handling of multiple workspace folders, not in the core.

Reported first to support@anthropic.com, who directed me here as the channel
engineering monitors for extension-specific defects.

Environment

• Extension: anthropic.claude-code 2.1.221-darwin-arm64 (installed 2026-08-04 11:39 local)
• Claude Code CLI (standalone): 2.1.221
• Host IDE: Antigravity IDE 2.1.1 (com.google.antigravity-ide)
• OS: macOS 26.5.2 (25F84), arm64
• permissions.defaultMode: "auto"

Steps to reproduce

1. Open the IDE with a single folder, ProjectA.
2. File > Add Folder to Workspace > ProjectB.
3. Start a new Claude Code session.
4. Send any message.

Expected

The session responds, as it does with a single-folder workspace.

Actual

The session hangs before producing any output. The stop button does not respond.
Closing the session is the only recovery.

Evidence

• The IDE lockfile for the hung session correctly lists both folders, so the folder

list does reach the extension:

~/.claude/ide/<port>.lock ->
{"pid":<pid>,"workspaceFolders":["/Users/<user>/.../ProjectA",
"/Users/<user>/.../ProjectB"],"ideName":"Antigravity IDE","transport":"ws"}

• No transcript file was ever created under ~/.claude/projects/ for that session,

i.e. it hung before persisting anything. Combined with the unresponsive stop
button, this points to a block upstream of the session loop rather than a
stalled API call.

Controls (what rules out other causes)

• Single-folder workspace, same IDE process (same pid), same day, a folder in the

same parent tree: works normally (session ran for 2+ hours).

• Same two folders via the standalone CLI at the same version 2.1.221:

cd ProjectA && claude --add-dir ProjectB works both interactively (responds in
seconds) and headless (claude -p "..." --add-dir ... completed in 8s, exit 0).
Same engine version, same folders, same configuration — it only fails through
the IDE extension.

• Not a SessionStart hook: mine runs in 14 ms with a 10 s timeout, and fired

identically in the working single-folder session.

• Not project size: the two folders contain 13 and 4 files respectively.
• Not a trust prompt: permissions.defaultMode is "auto", and no trust dialog

appears in the terminal for the same folders.

• Not an MCP server: the only configured MCP server is global, so it was equally

present in the working CLI control.

Regression note

The extension was updated to 2.1.221 on the morning of 2026-08-04 and the hang was
first observed the same afternoon. Multi-root workspaces worked before. I cannot
confirm which earlier version was in use, so treat the correlation as indicative.

Paths are anonymised. Happy to provide debug logs on request.