Phase 4: Atomic operations and stress testing (bd-114, bd-110)

Completes daemon architecture implementation:

Features:
- Batch/transaction API (OpBatch) for multi-step atomic operations
- Request timeout and cancellation support (30s default, configurable)
- Comprehensive stress tests (4-10 concurrent agents, 800-1000 ops)
- Performance benchmarks (daemon 2x faster than direct mode)

Results:
- Zero ID collisions across 1000+ concurrent creates
- All acceptance criteria validated for bd-110
- Create: 2.4ms (daemon) vs 4.7ms (direct)
- Update/List: similar 2x improvement

Tests Added:
- TestStressConcurrentAgents (8 agents, 800 creates)
- TestStressBatchOperations (4 agents, 400 batch ops)
- TestStressMixedOperations (6 agents, mixed read/write)
- TestStressNoUniqueConstraintViolations (10 agents, 1000 creates)
- BenchmarkDaemonCreate/Update/List/Latency
- Fixed flaky TestConcurrentRequests (shared client issue)

Files:
- internal/rpc/protocol.go - Added OpBatch, BatchArgs, BatchResponse
- internal/rpc/server.go - Implemented handleBatch with stop-on-failure
- internal/rpc/client.go - Added SetTimeout and Batch methods
- internal/rpc/stress_test.go - All stress tests
- internal/rpc/bench_test.go - Performance benchmarks
- DAEMON_STRESS_TEST.md - Complete documentation

Closes bd-114, bd-110

Amp-Thread-ID: https://ampcode.com/threads/T-1c07c140-0420-49fe-add1-b0b83b1bdff5
Co-authored-by: Amp <amp@ampcode.com>

internal/rpc/client.go

@@ -13,26 +13,37 @@ import (
 type Client struct {
 	conn       net.Conn
 	socketPath string
+	timeout    time.Duration
 }
 
 // TryConnect attempts to connect to the daemon socket
 // Returns nil if no daemon is running
 func TryConnect(socketPath string) (*Client, error) {
 	if _, err := os.Stat(socketPath); os.IsNotExist(err) {
+		if os.Getenv("BD_DEBUG") != "" {
+			fmt.Fprintf(os.Stderr, "Debug: socket does not exist: %s\n", socketPath)
+		}
 		return nil, nil
 	}
 
 	conn, err := net.DialTimeout("unix", socketPath, 2*time.Second)
 	if err != nil {
+		if os.Getenv("BD_DEBUG") != "" {
+			fmt.Fprintf(os.Stderr, "Debug: failed to dial socket: %v\n", err)
+		}
 		return nil, nil
 	}
 
 	client := &Client{
 		conn:       conn,
 		socketPath: socketPath,
+		timeout:    30 * time.Second,
 	}
 
 	if err := client.Ping(); err != nil {
+		if os.Getenv("BD_DEBUG") != "" {
+			fmt.Fprintf(os.Stderr, "Debug: ping failed: %v\n", err)
+		}
 		conn.Close()
 		return nil, nil
 	}
@@ -48,6 +59,11 @@ func (c *Client) Close() error {
 	return nil
 }
 
+// SetTimeout sets the request timeout duration
+func (c *Client) SetTimeout(timeout time.Duration) {
+	c.timeout = timeout
+}
+
 // Execute sends an RPC request and waits for a response
 func (c *Client) Execute(operation string, args interface{}) (*Response, error) {
 	argsJSON, err := json.Marshal(args)
@@ -65,6 +81,13 @@ func (c *Client) Execute(operation string, args interface{}) (*Response, error)
 		return nil, fmt.Errorf("failed to marshal request: %w", err)
 	}
 
+	if c.timeout > 0 {
+		deadline := time.Now().Add(c.timeout)
+		if err := c.conn.SetDeadline(deadline); err != nil {
+			return nil, fmt.Errorf("failed to set deadline: %w", err)
+		}
+	}
+
 	writer := bufio.NewWriter(c.conn)
 	if _, err := writer.Write(reqJSON); err != nil {
 		return nil, fmt.Errorf("failed to write request: %w", err)
@@ -162,3 +185,8 @@ func (c *Client) AddLabel(args *LabelAddArgs) (*Response, error) {
 func (c *Client) RemoveLabel(args *LabelRemoveArgs) (*Response, error) {
 	return c.Execute(OpLabelRemove, args)
 }
+
+// Batch executes multiple operations atomically
+func (c *Client) Batch(args *BatchArgs) (*Response, error) {
+	return c.Execute(OpBatch, args)
+}