feat: adopt Ralph pattern — pipe to claude (no --print), working Stop hook

loop.sh

@@ -188,40 +188,33 @@ fi
 
 # --- Agent runner ---
 # Runs a prompt through the selected AI tool.
-# Two modes:
-#   Interactive (default when TTY available): runs claude in full interactive mode.
-#     The user sees the complete CC session (tool calls, file edits, etc.) in the terminal.
-#     No output capture — state is tracked via prd.json and .verdict file.
-#   Headless (no TTY or LOOP_HEADLESS=true): uses claude --print for fully autonomous operation.
-#     Output is captured to a temp file for verdict parsing.
 #
-# The function prints captured output to stdout (headless) or nothing (interactive).
+# Interactive (default): Pipes prompt to claude WITHOUT --print.
+#   This gives the full interactive CC UI — tool calls, file edits, etc.
+#   A Stop hook (installed at startup) sends SIGINT to the loop when claude
+#   finishes, which returns control to the while loop for the next iteration.
+#   State is tracked via files (prd.json, .verdict), not stdout.
+#
+# Headless (LOOP_HEADLESS=true): Uses claude --print for CI/background.
+#   Output captured to file for verdict parsing.
 run_agent() {
     local prompt="$1"
-    local role="${2:-}"  # "generator" or "evaluator" — used for verdict file
+    local role="${2:-}"
 
-    # Clean up any previous verdict file
     rm -f "$LOOP_DIR/.verdict"
 
-    # Determine whether we can run interactively
-    local has_tty=false
-    if [ "${LOOP_HEADLESS:-false}" != "true" ] && { true > /dev/tty; } 2>/dev/null; then
-        has_tty=true
-    fi
-
-    # Run in subshell so a non-zero exit from the AI tool doesn't kill the loop.
     local agent_exit=0
-    if [ "$has_tty" = true ]; then
-        # --- Interactive mode ---
-        # Run claude directly in the terminal — full interactive UI visible.
-        # No output capture. State tracked via files (prd.json, .verdict).
+    if [ "${LOOP_HEADLESS:-false}" != "true" ]; then
+        # --- Interactive mode (Ralph pattern) ---
+        # Pipe prompt to claude without --print — full interactive UI.
+        # The Stop hook handles session exit.
         (
             case "$TOOL" in
                 claude)
-                    claude --dangerously-skip-permissions "$prompt"
+                    printf '%s\n' "$prompt" | claude --dangerously-skip-permissions
                     ;;
                 amp)
-                    amp --dangerously-allow-all "$prompt"
+                    printf '%s\n' "$prompt" | amp --dangerously-allow-all
                     ;;
                 *)
                     log "ERROR: Unknown tool '$TOOL'"
@@ -230,7 +223,9 @@ run_agent() {
             esac
         ) || agent_exit=$?
 
-        # In interactive mode, read verdict from file if evaluator wrote one
+        sleep 2  # Brief pause between sessions
+
+        # Read verdict from file if evaluator wrote one
         if [ "$role" = "evaluator" ] && [ -f "$LOOP_DIR/.verdict" ]; then
             cat "$LOOP_DIR/.verdict"
         fi