C:/Program Files/Git/plugin marketplace add silently fails to persist absolute Windows path

Description

/plugin marketplace add reports success but does not actually persist the marketplace entry to known_marketplaces.json when given an absolute Windows path. The tilde-expanded form works correctly, so this looks like a path-handling bug specific to absolute Windows paths.

Repro

1. Windows host, Claude Code session (any cwd)
2. Run: /plugin marketplace add C:/Users/<username>/Apps/marb-shared
3. Output: Successfully added marketplace: marbtrek
4. Inspect ~/.claude/plugins/known_marketplaces.json — the entry is not present.
5. Subsequent /plugin marketplace list does not show the marketplace.

Expected

The marketplace entry should be persisted to known_marketplaces.json, matching the "Successfully added" message that's shown in the chat.

Actual

The success message is shown but no persistence occurs. From the user's perspective the command silently no-ops while pretending to have succeeded.

Workaround

Use the tilde-expanded form: /plugin marketplace add ~/Apps/marb-shared — this writes to known_marketplaces.json correctly.

Environment

• OS: Windows 11 Pro 10.0.26200
• Shell: PowerShell 7+ / Git Bash
• Claude Code: latest as of 2026-04-29

Notes

I have not confirmed whether this also fails for absolute paths with backslashes (C:\Users\...) — the path I tried used forward slashes. Worth checking both forms.