Claude Code extension hangs in multi-root workspaces (Add Folder to Workspace)

Google Antigravity
,
1

Reporting here for visibility. The defect is in the Anthropic-published
extension (anthropic.claude-code), and I have filed it upstream with
Anthropic — but it only surfaces inside Antigravity, so it may involve how
Antigravity reports a multi-folder workspace to the extension.

Summary. With more than one folder in the workspace, a new Claude Code
session never responds. The spinner runs forever, the stop button is
unresponsive, and closing the session is the only way to recover.

Environment

  • Antigravity IDE 2.1.1 (com.google.antigravity-ide)
  • Bundled extension: anthropic.claude-code 2.1.221-darwin-arm64
  • macOS 26.5.2 (25F84), arm64

Steps to reproduce

  1. Open Antigravity 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: it hangs before producing any output. No transcript file is ever
written under ~/.claude/projects/, so it blocks before the session loop
starts. The interrupt button does nothing.

What rules out other causes

  • A single-folder workspace in the same Antigravity process works fine (that
    session ran for over two hours the same day).
  • The same two folders, driven by the standalone Claude Code CLI at the very
    same version 2.1.221, work correctly — both interactively
    (cd ProjectA && claude --add-dir ProjectB) and headless (8 seconds,
    exit code 0). Same engine version, same folders, same configuration: it only
    fails through the IDE.
  • Not a trust prompt (permissions.defaultMode is auto, and no dialog appears
    in the terminal), not project size (13 and 4 files), not a user SessionStart
    hook (14 ms, 10 s timeout, and it fired identically in the working session).

The IDE lockfile shows the folder list reaching the extension correctly:

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

The extension was updated to 2.1.221 on the morning of 2026-08-04 and the hang
appeared the same afternoon; multi-root workspaces worked before. I cannot
confirm the previous version, so treat that correlation as indicative only.

Has anyone else hit this since the last extension update?