Session hangs on startup when additionalDirectories contains unreachable network drive path (Windows)

Bug Description

When ~/.claude/settings.json contains an additionalDirectories entry pointing to a network drive that is not currently mounted (e.g., Z:\scripts when the NAS is offline), Claude Code hangs indefinitely during session startup, resulting in a 60-second handshake timeout.

Steps to Reproduce

1. Mount a network drive (e.g., Z: → NAS share)
2. In a Claude Code session, approve access to a path on that drive (e.g., Z:\scripts)
3. This adds Z:\scripts to permissions.additionalDirectories in ~/.claude/settings.json
4. Disconnect from the network / unmount the drive
5. Try to start a new Claude Code session → hangs indefinitely

Expected Behavior

Claude Code should either:

• Skip unreachable directories with a warning instead of hanging
• Use a timeout when scanning additionalDirectories paths
• Not block session startup on directory enumeration

Actual Behavior

Session startup blocks completely. No error message is shown. After 60 seconds, a handshake timeout occurs (in VS Code extension) or the CLI just hangs.

Root Cause Investigation

Through binary search on the settings.json entries, I isolated the exact blocker: a single additionalDirectories entry pointing to an unmounted network drive (Z:\scripts). Removing just that one entry immediately fixed the startup.

This is a common scenario for users who work from different locations (e.g., home with NAS vs. mobile/train without NAS).

The 803 permission rules and 13 hooks in the same settings.json were NOT the problem — all were restored successfully after removing the unreachable path.

Environment

• OS: Windows 11 Pro 10.0.26200
• Claude Code: 2.1.109 (VS Code Extension + CLI)
• Shell: Git Bash

Related Issues

• #46647 (Handshake timeout — same symptom, possibly same root cause for some users)
• #29935 (UNC paths in settings.json)
• #24140 (Symlinked .claude on network drive)

Workaround

I wrote a SessionStart hook that warns about unreachable paths at session start. However, this only warns after startup — it cannot prevent the hang since the directory scanning happens before hooks run.

The real fix needs to be in Claude Code's startup sequence: additionalDirectories scanning should have a timeout or use non-blocking I/O.