Add async git status to avoid blocking prompt

The prompt now fetches git status asynchronously using zsh's zle -F
mechanism. This provides p10k-like responsiveness:

1. Prompt appears immediately with directory only
2. Git info (branch, staged, unstaged, untracked) loads in background
3. Prompt updates automatically when git status completes

Uses native zsh features (exec fd redirection, zle -F callbacks) with
no external dependencies.

Author: claude

dot_prompt.zsh

@@ -1,21 +1,106 @@
 # Simple, reliable prompt similar to p10k lean style
 # Shows: directory, git info, command execution time, exit status
+# Git status is fetched asynchronously to avoid blocking
 
 # Enable colors
 autoload -U colors && colors
 
-# Enable vcs_info for git status
-autoload -Uz vcs_info
-zstyle ':vcs_info:*' enable git
-zstyle ':vcs_info:*' check-for-changes true
-zstyle ':vcs_info:*' stagedstr '%F{green}+'
-zstyle ':vcs_info:*' unstagedstr '%F{yellow}!'
-zstyle ':vcs_info:git:*' formats '%F{cyan}%b%f%c%u'
-zstyle ':vcs_info:git:*' actionformats '%F{cyan}%b%f|%F{red}%a%f%c%u'
+# ============================================================================
+# Async git status
+# ============================================================================
 
-# Track command execution time
+# State variables
+_prompt_git_info=""
 _prompt_exec_start=0
 _prompt_exec_time=0
+_prompt_exit_code=0
+_prompt_async_fd=""
+_prompt_async_pid=""
+
+# Get git status synchronously (called in background)
+_prompt_git_status() {
+  cd -q "$1" 2>/dev/null || return
+
+  # Check if we're in a git repo
+  local branch
+  branch=$(git symbolic-ref --short HEAD 2>/dev/null) || \
+  branch=$(git rev-parse --short HEAD 2>/dev/null) || return
+
+  local result="%F{cyan}${branch}%f"
+
+  # Check for staged changes
+  if ! git diff --cached --quiet 2>/dev/null; then
+    result+="%F{green}+%f"
+  fi
+
+  # Check for unstaged changes
+  if ! git diff --quiet 2>/dev/null; then
+    result+="%F{yellow}!%f"
+  fi
+
+  # Check for untracked files
+  if [[ -n $(git ls-files --others --exclude-standard 2>/dev/null | head -1) ]]; then
+    result+="%F{blue}?%f"
+  fi
+
+  echo " ${result}"
+}
+
+# Callback when async job completes
+_prompt_async_callback() {
+  local fd="$1"
+
+  # Read result from file descriptor
+  _prompt_git_info=""
+  if [[ -n "$fd" ]] && read -r -u "$fd" _prompt_git_info 2>/dev/null; then
+    : # Successfully read
+  fi
+
+  # Clean up file descriptor
+  if [[ -n "$_prompt_async_fd" ]]; then
+    zle -F "$_prompt_async_fd" 2>/dev/null
+    exec {_prompt_async_fd}<&- 2>/dev/null
+    _prompt_async_fd=""
+  fi
+
+  _prompt_async_pid=""
+
+  # Redraw prompt with new git info
+  zle && zle reset-prompt
+}
+
+# Start async git status fetch
+_prompt_async_start() {
+  # Kill any existing async job
+  if [[ -n "$_prompt_async_pid" ]]; then
+    kill "$_prompt_async_pid" 2>/dev/null
+    _prompt_async_pid=""
+  fi
+
+  # Clean up old file descriptor
+  if [[ -n "$_prompt_async_fd" ]]; then
+    zle -F "$_prompt_async_fd" 2>/dev/null
+    exec {_prompt_async_fd}<&- 2>/dev/null
+    _prompt_async_fd=""
+  fi
+
+  # Clear git info while loading
+  _prompt_git_info=""
+
+  # Quick check: are we in a git repo at all?
+  git rev-parse --is-inside-work-tree &>/dev/null || return
+
+  # Start background job and capture output via fd
+  exec {_prompt_async_fd}< <(_prompt_git_status "$PWD")
+  _prompt_async_pid=$!
+
+  # Register callback for when data is available
+  zle -F "$_prompt_async_fd" _prompt_async_callback
+}
+
+# ============================================================================
+# Prompt hooks
+# ============================================================================
 
 preexec() {
   _prompt_exec_start=$EPOCHREALTIME
@@ -35,10 +120,14 @@ precmd() {
   # Store exit code for prompt
   _prompt_exit_code=$exit_code
 
-  # Update vcs_info
-  vcs_info
+  # Start async git status fetch
+  _prompt_async_start
 }
 
+# ============================================================================
+# Prompt segments
+# ============================================================================
+
 # Format execution time (only show if > 3 seconds)
 _prompt_format_time() {
   (( _prompt_exec_time < 3 )) && return
@@ -67,29 +156,18 @@ _prompt_char() {
   fi
 }
 
-# Git info with untracked files indicator
-_prompt_git() {
-  [[ -z "${vcs_info_msg_0_}" ]] && return
-
-  local git_info="${vcs_info_msg_0_}"
-
-  # Check for untracked files
-  if command git status --porcelain 2>/dev/null | grep -q '^??'; then
-    git_info+='%F{blue}?%f'
-  fi
-
-  echo " ${git_info}"
-}
-
 # Right prompt with time
 _prompt_time() {
   echo "%F{8}%T%f"
 }
 
+# ============================================================================
 # Set prompts
+# ============================================================================
+
 setopt PROMPT_SUBST
 
-PROMPT='%F{blue}%~%f$(_prompt_git)
+PROMPT='%F{blue}%~%f${_prompt_git_info}
 $(_prompt_char) '
 
 RPROMPT='$(_prompt_format_time)$(_prompt_time)'