fix(agent): agent socket exceeds macos sun_path limit

pkg/config/pathmanager_darwin.go

@@ -55,6 +55,16 @@ func (d *darwinPathManager) StateDir() (string, error) {
 	return ensureDir(filepath.Join(home, "."+RepoName, "state"))
 }
 
+// RuntimeDir returns a directory for runtime state, such as sockets and PID files.
 func (d *darwinPathManager) RuntimeDir() (string, error) {
-	return ensureDir(filepath.Join(os.TempDir(), fmt.Sprintf("%s-%d", RepoName, os.Getuid())))
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return "", fmt.Errorf("runtime dir: %w", err)
+	}
+
+	dir, err := ensureDir(filepath.Join(home, "."+RepoName, "run"))
+	if err != nil {
+		return "", err
+	}
+	return dir, nil
 }

pkg/ssh/server/agent.go

@@ -15,11 +15,8 @@ import (
 const (
 	agentSocketDirPrefix = "devsy-ssh-agent-"
 
-	// maxAgentSocketPath is the most restrictive Unix-domain socket path
-	// length across supported platforms (macOS/BSD: sun_path[104];
-	// Linux: sun_path[108]). bind(2) returns EINVAL when exceeded, which
-	// surfaces as "invalid argument" — a confusing error far from the cause.
-	// We check eagerly and fail with a clear message instead.
+	// maxAgentSocketPath is the size of the OS sun_path array. bind(2) returns
+	// EINVAL when the path length reaches this limit.
 	maxAgentSocketPath = 104
 
 	// agentListenFile mirrors the socket filename ssh.NewAgentListener
@@ -149,20 +146,12 @@ func SweepStaleAgentSockets() {
 }
 
 // checkAgentSocketPathLen verifies the eventual unix socket path fits within
-// the OS sun_path limit. bind(2) returns the unhelpful EINVAL when it does
-// not, so we validate up front and emit a clear, actionable error that
-// names the offending path and the limit.
+// the OS sun_path limit.
 func checkAgentSocketPathLen(dir string) error {
 	sockPath := filepath.Join(dir, agentListenFile)
-	if len(sockPath) > maxAgentSocketPath {
-		log.Warnf(
-			"agent socket path exceeds max (%d > %d): %s",
-			len(sockPath),
-			maxAgentSocketPath,
-			sockPath,
-		)
+	if len(sockPath) >= maxAgentSocketPath {
 		return fmt.Errorf(
-			"agent socket path exceeds max (%d > %d): %s",
+			"agent socket path exceeds max (%d >= %d): %s",
 			len(sockPath),
 			maxAgentSocketPath,
 			sockPath,

pkg/ssh/server/agent_test.go

@@ -88,6 +88,20 @@ func TestCleanupAgentSocketDir(t *testing.T) {
 	})
 }
 
+func TestCheckAgentSocketPathLen_Boundary(t *testing.T) {
+	dirFor := func(pathLen int) string {
+		suffixLen := len(string(os.PathSeparator)) + len(agentListenFile)
+		return strings.Repeat("a", pathLen-suffixLen)
+	}
+
+	assert.NoError(t, checkAgentSocketPathLen(dirFor(maxAgentSocketPath-1)),
+		"path of maxAgentSocketPath-1 must be accepted")
+	assert.Error(t, checkAgentSocketPathLen(dirFor(maxAgentSocketPath)),
+		"path of exactly maxAgentSocketPath must be rejected (kernel returns EINVAL)")
+	assert.Error(t, checkAgentSocketPathLen(dirFor(maxAgentSocketPath+1)),
+		"path over maxAgentSocketPath must be rejected")
+}
+
 func TestSetupConnectionAgentListener_BadRuntimeDir(t *testing.T) {
 	if runtime.GOOS == osWindows {
 		t.Skip("unix socket based test")