fix: session isolation and blocking wait for visual companion

- Each session gets unique temp directory (/tmp/brainstorm-{pid}-{timestamp})
- Server outputs screen_dir and screen_file in startup JSON
- stop-server.sh takes screen_dir arg and cleans up session directory
- Document blocking TaskOutput pattern: 10-min timeouts, retry up to 3x,
  then prompt user "let me know when you want to continue"

lib/brainstorm-server/CLAUDE-INSTRUCTIONS.md

@@ -15,18 +15,25 @@ Use the visual companion when you need to show:
 ## Lifecycle
 
 ```bash
-# Start server (returns JSON with URL)
+# Start server (returns JSON with URL and session paths)
 ${CLAUDE_PLUGIN_ROOT}/lib/brainstorm-server/start-server.sh
+# Returns: {"type":"server-started","port":52341,"url":"http://localhost:52341",
+#           "screen_dir":"/tmp/brainstorm-12345-1234567890",
+#           "screen_file":"/tmp/brainstorm-12345-1234567890/screen.html"}
+
+# Save screen_dir and screen_file from response!
 
 # Tell user to open the URL in their browser
 
-# Write screens to /tmp/brainstorm/screen.html (auto-refreshes)
+# Write screens to screen_file (auto-refreshes)
 
-# Wait for user feedback
-${CLAUDE_PLUGIN_ROOT}/lib/brainstorm-server/wait-for-event.sh /path/to/server.log
+# Wait for user feedback:
+# 1. Start watcher in background
+${CLAUDE_PLUGIN_ROOT}/lib/brainstorm-server/wait-for-event.sh $SCREEN_DIR/.server.log
+# 2. Immediately call TaskOutput(task_id, block=true) to wait for completion
 
-# When done, stop server
-${CLAUDE_PLUGIN_ROOT}/lib/brainstorm-server/stop-server.sh
+# When done, stop server (pass screen_dir)
+${CLAUDE_PLUGIN_ROOT}/lib/brainstorm-server/stop-server.sh $SCREEN_DIR
 ```
 
 ## Writing Screens

lib/brainstorm-server/index.js

@@ -81,5 +81,11 @@ chokidar.watch(SCREEN_FILE).on('change', () => {
 });
 
 server.listen(PORT, '127.0.0.1', () => {
-  console.log(JSON.stringify({ type: 'server-started', port: PORT, url: `http://localhost:${PORT}` }));
+  console.log(JSON.stringify({
+    type: 'server-started',
+    port: PORT,
+    url: `http://localhost:${PORT}`,
+    screen_dir: SCREEN_DIR,
+    screen_file: SCREEN_FILE
+  }));
 });

lib/brainstorm-server/start-server.sh

@@ -3,15 +3,19 @@
 # Usage: start-server.sh
 #
 # Starts server on a random high port, outputs JSON with URL
+# Each session gets its own temp directory to avoid conflicts
 # Server runs in background, PID saved for cleanup
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
-SCREEN_DIR="${BRAINSTORM_SCREEN_DIR:-/tmp/brainstorm}"
+
+# Generate unique session directory
+SESSION_ID="$$-$(date +%s)"
+SCREEN_DIR="/tmp/brainstorm-${SESSION_ID}"
 SCREEN_FILE="${SCREEN_DIR}/screen.html"
 PID_FILE="${SCREEN_DIR}/.server.pid"
 LOG_FILE="${SCREEN_DIR}/.server.log"
 
-# Ensure screen directory exists
+# Create fresh session directory
 mkdir -p "$SCREEN_DIR"
 
 # Kill any existing server
@@ -23,7 +27,7 @@ fi
 
 # Start server, capturing output to log file
 cd "$SCRIPT_DIR"
-node index.js > "$LOG_FILE" 2>&1 &
+BRAINSTORM_SCREEN="$SCREEN_FILE" node index.js > "$LOG_FILE" 2>&1 &
 SERVER_PID=$!
 echo "$SERVER_PID" > "$PID_FILE"
 

lib/brainstorm-server/stop-server.sh

@@ -1,14 +1,21 @@
 #!/bin/bash
-# Stop the brainstorm server and clean up
-# Usage: stop-server.sh
+# Stop the brainstorm server and clean up session directory
+# Usage: stop-server.sh <screen_dir>
+
+SCREEN_DIR="$1"
+
+if [[ -z "$SCREEN_DIR" ]]; then
+  echo '{"error": "Usage: stop-server.sh <screen_dir>"}'
+  exit 1
+fi
 
-SCREEN_DIR="${BRAINSTORM_SCREEN_DIR:-/tmp/brainstorm}"
 PID_FILE="${SCREEN_DIR}/.server.pid"
 
 if [[ -f "$PID_FILE" ]]; then
   pid=$(cat "$PID_FILE")
   kill "$pid" 2>/dev/null
-  rm -f "$PID_FILE"
+  # Clean up session directory
+  rm -rf "$SCREEN_DIR"
   echo '{"status": "stopped"}'
 else
   echo '{"status": "not_running"}'