[BUG] Code tab opens detached scratch workspace after 1.46388.1 update, breaking project .claude/commands

## Description

After a Claude Desktop app update to **1.46388.1** (auto-updated/relaunched ~2026-09-03 22:18 PT), new/reopened conversations in the Code tab are opening in a detached, anonymous "scratch workspace" instead of the project folder that was previously open/selected. This breaks any project-local `.claude/commands/*.md` custom slash command, since the session has no `.claude` directory to resolve them from.

## Expected behavior

A Code tab conversation should open attached to the project folder the user was working in (or the one they explicitly select), so project-local `.claude/commands/*.md` files resolve normally via `/`.

## Actual behavior

- New conversations land in `~/Library/Application Support/Claude/scratch-workspaces///scratch-/` with no project folder attached.
- The `/` autocomplete only surfaces items from the Skill catalog (SKILL.md-based skills) — it does not search `.claude/commands/*.md` at all, so a project command like `/mem` no longer even shows as a suggestion once the session has no project attached.
- This had been working continuously for the user for weeks before the update; nothing in the affected project's `.claude/commands/mem.md` file or its underlying CLI dependency changed in that window (last edits weeks prior), ruling out a project-side cause.

## Environment

- Claude Desktop macOS, version 1.46388.1
- Update staged/relaunched: 2026-09-03 ~21:53–22:18 PT (from local `config.json`: `updaterBannerStagedAt`, `version_first_launch`)

## Repro steps

1. Have a custom slash command installed at `/.claude/commands/foo.md`, previously working via `/foo` in a Code tab conversation rooted in ``.
2. Update Claude Desktop to 1.46388.1 (or start a fresh conversation after the update without explicitly picking a project folder).
3. Type `/foo` in the new conversation.

## Result

`/foo` is absent from autocomplete (only Skill-catalog matches show), and the session's working directory is an unattached scratch workspace rather than ``.

Start by reproducing on Claude Desktop macOS 1.46388.1 with a project containing .claude/commands/foo.md, then open a new Code tab conversation and type /foo. The issue names the scratch workspace path under ~/Library/Application Support/Claude/scratch-workspaces/ and the slash-command autocomplete as the key behavior. Done means the Code tab attaches to the selected project folder and project-local commands appear in autocomplete again.

索引モデルが issue の本文から書いたものです。