feat(v0.5.3): AttachExisting passive reattach helper

internal/session/attach.go

@@ -0,0 +1,29 @@
+package session
+
+import (
+	"github.com/warrenronsiek/ctask/internal/shell"
+)
+
+// attacher is the test seam used by AttachExisting. Production code calls
+// shell.AttachSession directly; tests override this variable to capture
+// invocations or simulate failures. Do not run tests that override this
+// variable in parallel — it is a package global.
+var attacher = shell.AttachSession
+
+// AttachExisting is the passive-reattach path. It is invoked when a tmux
+// session for the workspace already exists and the lease is fresh and local
+// (the original ctask owner is alive and heartbeating).
+//
+// AttachExisting performs no Preflight, writes no lease, captures no
+// manifest, starts no heartbeat, prints no banner, and runs no finalize.
+// It connects the user's terminal to the existing tmux session via
+// shell.AttachSession and returns when the user detaches or the session
+// ends. shell.AttachSession's contract handles failure-mode classification:
+// nil on clean exit, wrapped error on non-zero exit.
+//
+// If the session disappeared between the dispatcher's HasSession check
+// and this call, AttachSession returns an error and the user can retry —
+// the next invocation will hit the owner-create path.
+func AttachExisting(tmuxPath, name string) error {
+	return attacher(tmuxPath, name)
+}

internal/session/attach_test.go

@@ -0,0 +1,43 @@
+package session
+
+import (
+	"errors"
+	"testing"
+)
+
+// Tests in this file mutate the package-level `attacher` variable and must
+// not be run with t.Parallel().
+
+func TestAttachExistingDelegatesToAttacher(t *testing.T) {
+	called := 0
+	orig := attacher
+	attacher = func(tmuxPath, name string) error {
+		called++
+		if name != "ctask-test-abc" {
+			t.Errorf("name: got %q", name)
+		}
+		if tmuxPath != "/usr/bin/tmux" {
+			t.Errorf("tmuxPath: got %q", tmuxPath)
+		}
+		return nil
+	}
+	t.Cleanup(func() { attacher = orig })
+
+	if err := AttachExisting("/usr/bin/tmux", "ctask-test-abc"); err != nil {
+		t.Fatalf("AttachExisting: %v", err)
+	}
+	if called != 1 {
+		t.Errorf("expected 1 call, got %d", called)
+	}
+}
+
+func TestAttachExistingPropagatesAttachError(t *testing.T) {
+	want := errors.New("attach failed")
+	orig := attacher
+	attacher = func(_, _ string) error { return want }
+	t.Cleanup(func() { attacher = orig })
+
+	if err := AttachExisting("/usr/bin/tmux", "ctask-x"); !errors.Is(err, want) {
+		t.Errorf("expected %v, got %v", want, err)
+	}
+}