Plugin marketplace auto-update triggers SSH key unlock prompt on every new session (Linux/gnome-keyring)

Description

Since the plugin marketplace was introduced (~March 20, 2026), Claude Code triggers an SSH key unlock prompt (gnome-keyring) at the start of every new session in a new project directory. This is alarming to users — it looks like a potential security incident.

Root Cause (investigated)

On startup, Claude Code runs git fetch on the plugin marketplace repository:

https://github.com/anthropics/claude-plugins-official.git
→ ~/.claude/plugins/marketplaces/claude-plugins-official/

On Linux systems using gnome-keyring (Ubuntu, Pop!_OS, etc.), git's libsecret credential helper accesses the gnome-keyring wallet to look up GitHub HTTPS credentials. This causes the keyring to re-initialize its SSH agent component, which prompts for the passphrase of any SSH private key stored in the keyring — even though no SSH connection is being made.

Steps to Reproduce

1. Linux system with gnome-keyring and a passphrase-protected SSH key stored in the keyring, mapped to github.com
2. Start Claude Code in any new project directory
3. Submit the first prompt

Expected Behavior

No SSH key prompt — the plugin update is HTTPS-only and should not involve SSH keys.

Actual Behavior

gnome-keyring prompts: _"An application wants to access the private key 'user@github.com'"_

Impact

• Alarming to users (looks like a potential security incident / prompt injection attack)
• Happened 3 times before root cause was identified
• Occurs on every new session, not just once

Environment

• OS: Pop!_OS 22.04
• gnome-keyring with SSH agent integration enabled
• SSH key for github.com stored in keyring with passphrase

Suggested Fix

• Run the marketplace git fetch with GIT_TERMINAL_PROMPT=0 and GIT_ASKPASS=/bin/true to prevent credential lookups from triggering keyring access, or
• Cache/embed a read-only token for the public Anthropic repo so no credential lookup is needed, or
• Add a user setting to disable or control plugin marketplace auto-update frequency