diff --git a/internal/polecat/session_manager.go b/internal/polecat/session_manager.go
index f9b9c6ad..a77f646f 100644
--- a/internal/polecat/session_manager.go
+++ b/internal/polecat/session_manager.go
@@ -2,6 +2,7 @@
 package polecat
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"os"
@@ -29,6 +30,7 @@ func debugSession(context string, err error) {
 var (
 	ErrSessionRunning  = errors.New("session already running")
 	ErrSessionNotFound = errors.New("session not found")
+	ErrIssueInvalid    = errors.New("issue not found or tombstoned")
 )
 
 // SessionManager handles polecat session lifecycle.
@@ -161,6 +163,14 @@ func (m *SessionManager) Start(polecat string, opts SessionStartOptions) error {
 		workDir = m.clonePath(polecat)
 	}
 
+	// Validate issue exists and isn't tombstoned BEFORE creating session.
+	// This prevents CPU spin loops from agents retrying work on invalid issues.
+	if opts.Issue != "" {
+		if err := m.validateIssue(opts.Issue, workDir); err != nil {
+			return err
+		}
+	}
+
 	runtimeConfig := config.LoadRuntimeConfig(m.rig.Path)
 
 	// Ensure runtime settings exist in polecats/ (not polecats/<name>/) so we don't
@@ -449,6 +459,32 @@ func (m *SessionManager) StopAll(force bool) error {
 	return lastErr
 }
 
+// validateIssue checks that an issue exists and is not tombstoned.
+// This must be called before starting a session to avoid CPU spin loops
+// from agents retrying work on invalid issues.
+func (m *SessionManager) validateIssue(issueID, workDir string) error {
+	cmd := exec.Command("bd", "show", issueID, "--json") //nolint:gosec
+	cmd.Dir = workDir
+	output, err := cmd.Output()
+	if err != nil {
+		return fmt.Errorf("%w: %s", ErrIssueInvalid, issueID)
+	}
+
+	var issues []struct {
+		Status string `json:"status"`
+	}
+	if err := json.Unmarshal(output, &issues); err != nil {
+		return fmt.Errorf("parsing issue: %w", err)
+	}
+	if len(issues) == 0 {
+		return fmt.Errorf("%w: %s", ErrIssueInvalid, issueID)
+	}
+	if issues[0].Status == "tombstone" {
+		return fmt.Errorf("%w: %s is tombstoned", ErrIssueInvalid, issueID)
+	}
+	return nil
+}
+
 // hookIssue pins an issue to a polecat's hook using bd update.
 func (m *SessionManager) hookIssue(issueID, agentID, workDir string) error {
 	cmd := exec.Command("bd", "update", issueID, "--status=hooked", "--assignee="+agentID) //nolint:gosec