diff --git a/internal/cmd/doctor.go b/internal/cmd/doctor.go
index b95f9aee..ee6ff0d7 100644
--- a/internal/cmd/doctor.go
+++ b/internal/cmd/doctor.go
@@ -96,6 +96,9 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 	// Lifecycle hygiene checks
 	d.Register(doctor.NewLifecycleHygieneCheck())
 
+	// Hook attachment checks
+	d.Register(doctor.NewHookAttachmentValidCheck())
+
 	// Run checks
 	var report *doctor.Report
 	if doctorFix {
diff --git a/internal/doctor/hook_check.go b/internal/doctor/hook_check.go
new file mode 100644
index 00000000..4b6b2385
--- /dev/null
+++ b/internal/doctor/hook_check.go
@@ -0,0 +1,186 @@
+package doctor
+
+import (
+	"fmt"
+	"os/exec"
+	"path/filepath"
+	"strings"
+
+	"github.com/steveyegge/gastown/internal/beads"
+)
+
+// HookAttachmentValidCheck verifies that attached molecules exist and are not closed.
+// This detects when a hook's attached_molecule field points to a non-existent or
+// closed issue, which can leave agents with stale work assignments.
+type HookAttachmentValidCheck struct {
+	FixableCheck
+	invalidAttachments []invalidAttachment
+}
+
+type invalidAttachment struct {
+	pinnedBeadID   string
+	pinnedBeadDir  string // Directory where the pinned bead was found
+	moleculeID     string
+	reason         string // "not_found" or "closed"
+}
+
+// NewHookAttachmentValidCheck creates a new hook attachment validation check.
+func NewHookAttachmentValidCheck() *HookAttachmentValidCheck {
+	return &HookAttachmentValidCheck{
+		FixableCheck: FixableCheck{
+			BaseCheck: BaseCheck{
+				CheckName:        "hook-attachment-valid",
+				CheckDescription: "Verify attached molecules exist and are not closed",
+			},
+		},
+	}
+}
+
+// Run checks all pinned beads for invalid molecule attachments.
+func (c *HookAttachmentValidCheck) Run(ctx *CheckContext) *CheckResult {
+	c.invalidAttachments = nil
+
+	var details []string
+
+	// Check town-level beads
+	townBeadsDir := filepath.Join(ctx.TownRoot, ".beads")
+	townInvalid := c.checkBeadsDir(townBeadsDir, "town")
+	for _, inv := range townInvalid {
+		details = append(details, c.formatInvalid(inv))
+	}
+	c.invalidAttachments = append(c.invalidAttachments, townInvalid...)
+
+	// Check rig-level beads
+	rigDirs := c.findRigBeadsDirs(ctx.TownRoot)
+	for _, rigDir := range rigDirs {
+		rigName := filepath.Base(filepath.Dir(rigDir))
+		rigInvalid := c.checkBeadsDir(rigDir, rigName)
+		for _, inv := range rigInvalid {
+			details = append(details, c.formatInvalid(inv))
+		}
+		c.invalidAttachments = append(c.invalidAttachments, rigInvalid...)
+	}
+
+	if len(c.invalidAttachments) == 0 {
+		return &CheckResult{
+			Name:    c.Name(),
+			Status:  StatusOK,
+			Message: "All hook attachments are valid",
+		}
+	}
+
+	return &CheckResult{
+		Name:    c.Name(),
+		Status:  StatusError,
+		Message: fmt.Sprintf("Found %d invalid hook attachment(s)", len(c.invalidAttachments)),
+		Details: details,
+		FixHint: "Run 'gt doctor --fix' to detach invalid molecules, or 'gt mol detach <pinned-bead-id>' manually",
+	}
+}
+
+// checkBeadsDir checks all pinned beads in a directory for invalid attachments.
+func (c *HookAttachmentValidCheck) checkBeadsDir(beadsDir, location string) []invalidAttachment {
+	var invalid []invalidAttachment
+
+	b := beads.New(filepath.Dir(beadsDir))
+
+	// List all pinned beads
+	pinnedBeads, err := b.List(beads.ListOptions{
+		Status:   beads.StatusPinned,
+		Priority: -1,
+	})
+	if err != nil {
+		// Can't list pinned beads - silently skip this directory
+		return nil
+	}
+
+	for _, pinnedBead := range pinnedBeads {
+		// Parse attachment fields from the pinned bead
+		attachment := beads.ParseAttachmentFields(pinnedBead)
+		if attachment == nil || attachment.AttachedMolecule == "" {
+			continue // No attachment, skip
+		}
+
+		// Verify the attached molecule exists and is not closed
+		molecule, err := b.Show(attachment.AttachedMolecule)
+		if err != nil {
+			// Molecule not found
+			invalid = append(invalid, invalidAttachment{
+				pinnedBeadID:  pinnedBead.ID,
+				pinnedBeadDir: beadsDir,
+				moleculeID:    attachment.AttachedMolecule,
+				reason:        "not_found",
+			})
+			continue
+		}
+
+		if molecule.Status == "closed" {
+			invalid = append(invalid, invalidAttachment{
+				pinnedBeadID:  pinnedBead.ID,
+				pinnedBeadDir: beadsDir,
+				moleculeID:    attachment.AttachedMolecule,
+				reason:        "closed",
+			})
+		}
+	}
+
+	return invalid
+}
+
+// findRigBeadsDirs finds all rig-level .beads directories.
+func (c *HookAttachmentValidCheck) findRigBeadsDirs(townRoot string) []string {
+	var dirs []string
+
+	// Look for .beads directories in rig subdirectories
+	// Pattern: <townRoot>/<rig>/.beads (but NOT <townRoot>/.beads which is town-level)
+	cmd := exec.Command("find", townRoot, "-maxdepth", "2", "-type", "d", "-name", ".beads")
+	output, err := cmd.Output()
+	if err != nil {
+		return nil
+	}
+
+	for _, line := range strings.Split(strings.TrimSpace(string(output)), "\n") {
+		if line == "" {
+			continue
+		}
+		// Skip town-level .beads
+		if line == filepath.Join(townRoot, ".beads") {
+			continue
+		}
+		// Skip mayor directory
+		if strings.Contains(line, "/mayor/") {
+			continue
+		}
+		dirs = append(dirs, line)
+	}
+
+	return dirs
+}
+
+// formatInvalid formats an invalid attachment for display.
+func (c *HookAttachmentValidCheck) formatInvalid(inv invalidAttachment) string {
+	reasonText := "not found"
+	if inv.reason == "closed" {
+		reasonText = "is closed"
+	}
+	return fmt.Sprintf("%s: attached molecule %s %s", inv.pinnedBeadID, inv.moleculeID, reasonText)
+}
+
+// Fix detaches all invalid molecule attachments.
+func (c *HookAttachmentValidCheck) Fix(ctx *CheckContext) error {
+	var errors []string
+
+	for _, inv := range c.invalidAttachments {
+		b := beads.New(filepath.Dir(inv.pinnedBeadDir))
+
+		_, err := b.DetachMolecule(inv.pinnedBeadID)
+		if err != nil {
+			errors = append(errors, fmt.Sprintf("failed to detach from %s: %v", inv.pinnedBeadID, err))
+		}
+	}
+
+	if len(errors) > 0 {
+		return fmt.Errorf("%s", strings.Join(errors, "; "))
+	}
+	return nil
+}
diff --git a/internal/doctor/hook_check_test.go b/internal/doctor/hook_check_test.go
new file mode 100644
index 00000000..e2a8e770
--- /dev/null
+++ b/internal/doctor/hook_check_test.go
@@ -0,0 +1,123 @@
+package doctor
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestNewHookAttachmentValidCheck(t *testing.T) {
+	check := NewHookAttachmentValidCheck()
+
+	if check.Name() != "hook-attachment-valid" {
+		t.Errorf("expected name 'hook-attachment-valid', got %q", check.Name())
+	}
+
+	if check.Description() != "Verify attached molecules exist and are not closed" {
+		t.Errorf("unexpected description: %q", check.Description())
+	}
+
+	if !check.CanFix() {
+		t.Error("expected CanFix to return true")
+	}
+}
+
+func TestHookAttachmentValidCheck_NoBeadsDir(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	check := NewHookAttachmentValidCheck()
+	ctx := &CheckContext{TownRoot: tmpDir}
+
+	result := check.Run(ctx)
+
+	// No beads dir means nothing to check, should be OK
+	if result.Status != StatusOK {
+		t.Errorf("expected StatusOK when no beads dir, got %v", result.Status)
+	}
+}
+
+func TestHookAttachmentValidCheck_EmptyBeadsDir(t *testing.T) {
+	tmpDir := t.TempDir()
+	beadsDir := filepath.Join(tmpDir, ".beads")
+	if err := os.MkdirAll(beadsDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	check := NewHookAttachmentValidCheck()
+	ctx := &CheckContext{TownRoot: tmpDir}
+
+	result := check.Run(ctx)
+
+	// Empty beads dir means no pinned beads, should be OK
+	// Note: This may error if bd CLI is not available, but should still handle gracefully
+	if result.Status != StatusOK && result.Status != StatusError {
+		t.Errorf("expected StatusOK or graceful error, got %v", result.Status)
+	}
+}
+
+func TestHookAttachmentValidCheck_FormatInvalid(t *testing.T) {
+	check := NewHookAttachmentValidCheck()
+
+	tests := []struct {
+		inv      invalidAttachment
+		expected string
+	}{
+		{
+			inv: invalidAttachment{
+				pinnedBeadID: "hq-123",
+				moleculeID:   "gt-456",
+				reason:       "not_found",
+			},
+			expected: "hq-123: attached molecule gt-456 not found",
+		},
+		{
+			inv: invalidAttachment{
+				pinnedBeadID: "hq-123",
+				moleculeID:   "gt-789",
+				reason:       "closed",
+			},
+			expected: "hq-123: attached molecule gt-789 is closed",
+		},
+	}
+
+	for _, tt := range tests {
+		result := check.formatInvalid(tt.inv)
+		if result != tt.expected {
+			t.Errorf("formatInvalid() = %q, want %q", result, tt.expected)
+		}
+	}
+}
+
+func TestHookAttachmentValidCheck_FindRigBeadsDirs(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	// Create town-level .beads (should be excluded)
+	townBeads := filepath.Join(tmpDir, ".beads")
+	if err := os.MkdirAll(townBeads, 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	// Create rig-level .beads
+	rigBeads := filepath.Join(tmpDir, "myrig", ".beads")
+	if err := os.MkdirAll(rigBeads, 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	check := NewHookAttachmentValidCheck()
+	dirs := check.findRigBeadsDirs(tmpDir)
+
+	// Should find the rig-level beads but not town-level
+	found := false
+	for _, dir := range dirs {
+		if dir == townBeads {
+			t.Error("findRigBeadsDirs should not include town-level .beads")
+		}
+		if dir == rigBeads {
+			found = true
+		}
+	}
+
+	if !found && len(dirs) > 0 {
+		t.Logf("Found dirs: %v", dirs)
+	}
+}