Copilot CLI fails after macOS restart when persisted writer-lock device ID changes

[moonbox3]

Describe the bug

After updating to macOS 26.7.1 and restarting, Copilot CLI fails during MCP startup and request execution with:

The shared writer lock or its directory changed.

The same error occurs with copilot mcp list, preventing normal CLI use. Authentication succeeds.

The persisted writer-lock binding contains a filesystem device ID that differs from the current device ID, although the directory and lock-file inode IDs are unchanged.

Affected version

GitHub Copilot CLI 1.0.90

Steps to reproduce the behavior

1. Use Copilot CLI with existing configuration in ~/.copilot.
2. Update macOS to 26.7.1 and restart. This preceded the failure on my machine; I have not independently reproduced the OS update.
3. Launch copilot.

Observed:
"Failed to start MCP Servers: Error: The shared writer lock or its directory changed."

4. Submit a prompt.

Observed:
"Execution failed: Error: Request session.send failed with message: The shared writer lock or its directory changed."

5. Run copilot mcp list.

Observed:
"Error: The shared writer lock or its directory changed."

Expected behavior

Copilot should continue working after a macOS update/restart.

If a filesystem device-ID change invalidates the persisted writer-lock binding, Copilot should safely recover or provide an actionable recovery procedure.

Additional context

Environment:

• macOS 26.7.1, build 25G241
• Apple Silicon / arm64
• Shell: zsh

Diagnosis:
~/.copilot/.mcp-writer.binding contained:

{"root":{"platform":"unix","device":16777232,"inode":87818635},"lock":{"platform":"unix","device":16777232,"inode":241099151}}

Current filesystem metadata reported:

• ~/.copilot: device=16777233, inode=87818635
• ~/.copilot/.mcp-writer.lock: device=16777233, inode=241099151

Both inode IDs were unchanged; only the device IDs differed.

An empty temporary Copilot state directory allowed copilot mcp list to succeed.

Workaround:
Backed up .mcp-writer.binding and updated only its two device IDs to match current filesystem metadata while holding an exclusive writer lock.

Verification after repair:

• copilot mcp list succeeded.
• A fresh interactive session connected both MCP servers.
• A test prompt completed successfully.

The exact macOS mechanism behind the device-ID change is unconfirmed.

[moonbox3]

Duplicate of #4998.

Confirmed on macOS 26.7.1 with Copilot CLI 1.0.90. The persisted device ID changed from 16777232 to 16777233 while both inode IDs remained unchanged. Updating the two device IDs under an exclusive writer lock restored MCP startup and prompt execution.

Closing in favor of #4998.