fix(pipenv): cache version for completion checks

- Avoid running pipenv --version on every shell startup.
- Read the cached version when available and refresh it async.
- Use the cached value to select argcomplete or legacy completion.
- Document the Pipenv version and legacy completion caches.

plugins/pipenv/README.md

@@ -29,6 +29,18 @@ plugins=(... pipenv ...)
   - `pvenv` is aliased to `pipenv --venv`
   - `ppy` is aliased to `pipenv --py`
 
+## Cache
+
+This plugin caches the Pipenv version to avoid running `pipenv --version` on every shell startup. The cache is automatically refreshed asynchronously when the plugin is loaded, which is usually when you start a new terminal session.
+
+For legacy Pipenv versions, the generated completion script is also cached.
+
+The cache is stored at:
+
+- `$ZSH_CACHE_DIR/pipenv_version` version of Pipenv, used to choose between argcomplete-based completion and legacy Click-based completion.
+
+- `$ZSH_CACHE_DIR/completions/_pipenv` legacy Click-based completion script.
+
 ## Configuration
 
 ### Shell activation

plugins/pipenv/pipenv.plugin.zsh

@@ -11,7 +11,18 @@ fi
 
 autoload -Uz is-at-least
 
-_pipenv_version="${$(pipenv --version 2>/dev/null)#pipenv, version }"
+_pipenv_version_cache="$ZSH_CACHE_DIR/pipenv_version"
+
+if [[ -f "$_pipenv_version_cache" ]]; then
+  _pipenv_version="$(< "$_pipenv_version_cache" 2>/dev/null)"
+else
+  _pipenv_version="${$(pipenv --version 2>/dev/null)#pipenv, version }"
+fi
+
+{
+  _pipenv_fresh_version="${$(pipenv --version 2>/dev/null)#pipenv, version }"
+  [[ -n "$_pipenv_fresh_version" ]] && print -r -- "$_pipenv_fresh_version" >| "$_pipenv_version_cache"
+} &|
 
 if is-at-least 2026.5.0 "$_pipenv_version" && (( $+commands[register-python-argcomplete] )); then
   # argcomplete-based completion