[BUG] /plugin menu: install failure error flashes briefly and menu exits — error text unreadable, only recoverable via non-interactive CLI

Preflight Checklist

• [x] I have searched existing issues and this is not a duplicate
• [x] I am on the latest version of Claude Code

What's Wrong?

When a plugin install fails inside the interactive /plugin (plugins) menu, the error message flashes on screen for a fraction of a second and the menu immediately exits. The error text is unreadable and unrecoverable — it is not shown in the conversation, not written to any log I could find, and reopening the menu gives no indication of what failed.

The only way I could recover the actual error was to leave the TUI entirely and run the non-interactive CLI, which prints it fine:

claude plugin install db-context-engineering@data-agent-kit

In my case the underlying failure was the known SSH-only clone behavior for github / git-subdir marketplace sources (#9719, #26588 — machine has no GitHub SSH key, so git@github.com: clones fail with Permission denied (publickey)). That underlying issue is already tracked; this report is specifically about the menu UX destroying the error message, which turns a diagnosable one-line git error into "installs mysteriously don't work." Everything in the interactive path (marketplace browsing, plugin details) worked, so nothing pointed at git/SSH until the CLI was used.

What Should Happen?

• The install failure should be displayed persistently in the menu (or after it closes), requiring a keypress to dismiss, instead of flashing and exiting.
• Ideally the full error is also written somewhere retrievable (e.g. shown via a "last error" entry in the menu or logged to disk) so users can diagnose after the fact.

Error Messages/Logs

The flashed/hidden error, recovered via the non-interactive CLI:

Installing plugin "db-context-engineering@data-agent-kit"...✘ Failed to install plugin "db-context-engineering@data-agent-kit": Failed to clone repository for git-subdir source: Cloning into '/home/user/.claude/plugins/cache/temp_subdir_1786398965724_1w7bei.clone'...
git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.

Steps to Reproduce

1. Use a machine with no SSH key registered with GitHub (any machine where git clone git@github.com:owner/repo fails will do — the point is any install-time failure).
2. /plugin marketplace add https://github.com/GoogleCloudPlatform/data-agent-kit.git (this marketplace declares plugins with github + ref and git-subdir sources, which install over SSH).
3. Open the /plugin menu and install any plugin from that marketplace (e.g. looker or db-context-engineering).
4. Observe: an error flashes for a fraction of a second, the menu exits, and there is no way to read the error text.

Claude Code Version

2.1.226

Platform

CLI (terminal)

Operating System

Linux (kernel 6.6)

Terminal/Shell

bash

Additional Information

• The underlying SSH-only clone default is tracked in #9719 / #26588; a CLAUDE_CODE_PLUGIN_PREFER_HTTPS env var appears to exist in the 2.1.226 binary but is undocumented (#58859). This issue is only about the error presentation in the interactive menu.
• Workaround for the underlying failure, for anyone landing here: GIT_CONFIG_COUNT=1 GIT_CONFIG_KEY_0="url.https://github.com/.insteadOf" GIT_CONFIG_VALUE_0="git@github.com:" claude plugin install <name>@<marketplace>