Bug Description

When installing a plugin from a git URL (e.g., superpowers@git+https://github.com/obra/superpowers.git), opencode fails on Windows because it uses the raw URL as a directory name in the cache path.

Error

ENOENT: no such file or directory, mkdir 'C:\Users\Ivan\.cache\opencode\packages\superpowers@git+https:\github.com\obra\superpowers.git'

Root Cause

The plugin installer constructs the cache directory path by appending the raw package specifier (e.g., superpowers@git+https://github.com/obra/superpowers.git) directly to the packages cache directory. On Windows, the : character and path separators from the URL are invalid in file/directory names, causing mkdir to fail.

The problematic path transforms https:// into https:\ (backslash due to Windows path normalization), which contains a colon — a forbidden character in Windows filenames.

Reproduction Steps

1. On Windows, add a git-based plugin to opencode config:

   {
     "plugins": ["superpowers@git+https://github.com/obra/superpowers.git"]
   }

2. Run opencode run --print-logs "hello"
3. Observe the ENOENT error during plugin installation

Expected Behavior

The plugin should install successfully. The cache directory name should be derived from a URL-safe encoding (e.g., URL-encoding, hashing, or stripping invalid characters) of the git URL.

Actual Behavior

Installation fails with ENOENT because the cache directory path contains Windows-invalid characters (:).

Environment

Log Excerpt

INFO  service=plugin path=superpowers@git+https://github.com/obra/superpowers.git loading plugin
INFO  service=npm pkg=superpowers@git+https://github.com/obra/superpowers.git installing package
ERROR service=plugin pkg=superpowers version=git+https://github.com/obra/superpowers.git error=ENOENT: no such file or directory, mkdir 'C:\Users\Ivan\.cache\opencode\packages\superpowers@git+https:\github.com\obra\superpowers.git' failed to install plugin

Suggested Fix

When constructing the cache directory name for git-based plugins, sanitize the URL by either:

1. Hashing the URL (e.g., SHA-256 or MD5) to produce a safe directory name
2. URL-encoding or replacing invalid characters (:, /, <, >, |, ?, *) with safe alternatives
3. Using a combination of package name prefix + hash suffix for readability

This would also prevent similar issues with other URL-based package specifiers on Windows.