diff --git a/frontend/src/pages/ProceduralNavigationPage.tsx b/frontend/src/pages/ProceduralNavigationPage.tsx
index 81500dae..26fc7781 100644
--- a/frontend/src/pages/ProceduralNavigationPage.tsx
+++ b/frontend/src/pages/ProceduralNavigationPage.tsx
@@ -1,9 +1,12 @@
 import { useEffect, useState, useRef } from 'react'
 import { useParams, useNavigate, useLocation } from 'react-router-dom'
-import { ChevronLeft, ChevronRight, ListOrdered, Settings2, X } from 'lucide-react'
+import { ChevronLeft, ChevronRight, ListOrdered, Settings2, X, Plus } from 'lucide-react'
 import { treesApi } from '@/api/trees'
 import { sessionsApi } from '@/api/sessions'
-import type { Tree, Session, ProceduralStep, DecisionRecord } from '@/types'
+import { stepsApi } from '@/api/steps'
+import type { Tree, Session, ProceduralStep, DecisionRecord, RuntimeStep, CustomProceduralStep } from '@/types'
+import type { CustomStep } from '@/types/session'
+import type { Step } from '@/types/step'
 import { IntakeFormModal } from '@/components/procedural/IntakeFormModal'
 import { StepChecklist } from '@/components/procedural/StepChecklist'
 import { StepDetail } from '@/components/procedural/StepDetail'
@@ -17,6 +20,9 @@ import { StepFeedback } from '@/components/session/StepFeedback'
 import { CSATModal } from '@/components/session/CSATModal'
 import { hasBeenRated } from '@/components/session/csatUtils'
 import { MaintenanceContextStrip } from '@/components/maintenance/MaintenanceContextStrip'
+import { CustomStepModal } from '@/components/step-library/CustomStepModal'
+import type { CustomStepDraft } from '@/components/step-library/CustomStepModal'
+import { PostStepActionModal } from '@/components/session/PostStepActionModal'
 
 interface StepState {
   notes: string
@@ -24,6 +30,29 @@ interface StepState {
   completedAt: string | null
 }
 
+function buildRuntimeSteps(baseSteps: ProceduralStep[], customSteps: CustomStep[]): RuntimeStep[] {
+  const result: RuntimeStep[] = [...baseSteps]
+  const sorted = [...customSteps].sort((a, b) => a.timestamp.localeCompare(b.timestamp))
+  for (const cs of sorted) {
+    const afterIdx = result.findIndex((s) => s.id === cs.inserted_after_node_id)
+    const insertAt = afterIdx >= 0 ? afterIdx + 1 : result.length
+    const runtimeCustom: CustomProceduralStep = {
+      id: cs.id,
+      type: 'procedure_step',
+      title: cs.step_data.title,
+      description: cs.step_data.content?.instructions,
+      content_type: 'action',
+      commands: cs.step_data.content?.commands?.map((c) => ({
+        code: c.command,
+        label: c.label,
+      })),
+      isCustom: true,
+    }
+    result.splice(insertAt, 0, runtimeCustom)
+  }
+  return result
+}
+
 export function ProceduralNavigationPage() {
   const { id: treeId } = useParams<{ id: string }>()
   const navigate = useNavigate()
@@ -47,6 +76,15 @@ export function ProceduralNavigationPage() {
   const [batchProgress, setBatchProgress] = useState<{ completed: number; total: number } | null>(null)
   const timerRef = useRef<ReturnType<typeof setInterval> | null>(null)
 
+  // Custom step state
+  const [runtimeSteps, setRuntimeSteps] = useState<RuntimeStep[]>([])
+  const [sessionCustomSteps, setSessionCustomSteps] = useState<CustomStep[]>([])
+  const [showCustomStepModal, setShowCustomStepModal] = useState(false)
+  const [showPostStepModal, setShowPostStepModal] = useState(false)
+  const [pendingCustomStep, setPendingCustomStep] = useState<Step | CustomStepDraft | null>(null)
+  const [pendingIsFromLibrary, setPendingIsFromLibrary] = useState(false)
+  const [isSavingStep, setIsSavingStep] = useState(false)
+
   // Get procedural steps from tree
   const getSteps = (): ProceduralStep[] => {
     if (!tree) return []
@@ -55,7 +93,7 @@ export function ProceduralNavigationPage() {
   }
 
   const steps = getSteps()
-  const procedureSteps = steps.filter((s) => s.type === 'procedure_step')
+  const procedureSteps = runtimeSteps.filter((s) => s.type === 'procedure_step')
   const completedStepIds = new Set(
     Array.from(stepStates.entries())
       .filter(([, state]) => state.completedAt)
@@ -63,7 +101,7 @@ export function ProceduralNavigationPage() {
   )
 
   const estimatedTotalMinutes = procedureSteps.reduce(
-    (sum, step) => sum + (step.estimated_minutes || 0),
+    (sum, step) => sum + (('estimated_minutes' in step ? step.estimated_minutes : undefined) || 0),
     0
   )
 
@@ -159,6 +197,8 @@ export function ProceduralNavigationPage() {
         initialStates.set(step.id, { notes: '', verificationValue: '', completedAt: null })
       }
       setStepStates(initialStates)
+      setRuntimeSteps(allSteps)
+      setSessionCustomSteps([])
     } catch {
       toast.error('Failed to start session')
     }
@@ -173,6 +213,13 @@ export function ProceduralNavigationPage() {
 
       // Initialize step states from session decisions
       const allSteps = getStepsFromTree(treeData)
+
+      // Initialize custom steps from session data
+      const customSteps = sessionData.custom_steps || []
+      setSessionCustomSteps(customSteps)
+      const hydrated = buildRuntimeSteps(allSteps, customSteps)
+      setRuntimeSteps(hydrated)
+
       const initialStates = new Map<string, StepState>()
       for (const step of allSteps) {
         initialStates.set(step.id, { notes: '', verificationValue: '', completedAt: null })
@@ -191,7 +238,7 @@ export function ProceduralNavigationPage() {
       setStepStates(initialStates)
 
       // Set current step to first incomplete step
-      const pSteps = allSteps.filter((s) => s.type === 'procedure_step')
+      const pSteps = hydrated.filter((s) => s.type === 'procedure_step')
       const firstIncomplete = pSteps.findIndex((s) => !initialStates.get(s.id)?.completedAt)
       setCurrentStepIndex(firstIncomplete >= 0 ? firstIncomplete : pSteps.length - 1)
     } catch {
@@ -303,6 +350,112 @@ export function ProceduralNavigationPage() {
     setShowCsatModal(false)
   }
 
+  const handleStepCreated = (step: Step | CustomStepDraft, isFromLibrary: boolean) => {
+    setPendingCustomStep(step)
+    setPendingIsFromLibrary(isFromLibrary)
+    setShowCustomStepModal(false)
+    setShowPostStepModal(true)
+  }
+
+  const handleInsertCustomStep = async (step: Step | CustomStepDraft) => {
+    if (!session) return
+
+    const id = crypto.randomUUID()
+    const currentStep = procedureSteps[currentStepIndex]
+    const insertedAfterId = currentStep?.id ?? ''
+
+    const runtimeCustom: CustomProceduralStep = {
+      id,
+      type: 'procedure_step',
+      title: step.title,
+      description: step.content?.instructions,
+      content_type: 'action',
+      commands: step.content?.commands?.map((c) => ({
+        code: c.command,
+        label: c.label,
+      })),
+      isCustom: true,
+    }
+
+    setRuntimeSteps((prev) => {
+      const next = [...prev]
+      const globalIdx = next.findIndex((s) => s.id === insertedAfterId)
+      const insertAt = globalIdx >= 0 ? globalIdx + 1 : next.length
+      next.splice(insertAt, 0, runtimeCustom)
+      return next
+    })
+
+    setStepStates((prev) => {
+      const next = new Map(prev)
+      next.set(id, { notes: '', verificationValue: '', completedAt: null })
+      return next
+    })
+
+    const newCustomStep: CustomStep = {
+      id,
+      inserted_after_node_id: insertedAfterId,
+      step_data: step,
+      timestamp: new Date().toISOString(),
+    }
+    const newCustomSteps = [...sessionCustomSteps, newCustomStep]
+    setSessionCustomSteps(newCustomSteps)
+
+    try {
+      await sessionsApi.update(session.id, { custom_steps: newCustomSteps })
+    } catch {
+      toast.error('Failed to save custom step')
+    }
+
+    setCurrentStepIndex(currentStepIndex + 1)
+  }
+
+  const handleSaveForLater = async () => {
+    if (!pendingCustomStep || pendingIsFromLibrary) return
+    setIsSavingStep(true)
+    try {
+      await stepsApi.create({
+        title: pendingCustomStep.title,
+        step_type: pendingCustomStep.step_type,
+        content: pendingCustomStep.content,
+        visibility: 'private',
+      })
+      toast.success('Step saved to library')
+    } catch {
+      toast.error('Failed to save step')
+    } finally {
+      setIsSavingStep(false)
+      setShowPostStepModal(false)
+      setPendingCustomStep(null)
+    }
+  }
+
+  const handleUseNow = async () => {
+    if (!pendingCustomStep) return
+    setShowPostStepModal(false)
+    await handleInsertCustomStep(pendingCustomStep)
+    setPendingCustomStep(null)
+  }
+
+  const handleBoth = async () => {
+    if (!pendingCustomStep || pendingIsFromLibrary) return
+    setIsSavingStep(true)
+    try {
+      await stepsApi.create({
+        title: pendingCustomStep.title,
+        step_type: pendingCustomStep.step_type,
+        content: pendingCustomStep.content,
+        visibility: 'private',
+      })
+    } catch {
+      toast.error('Failed to save step to library')
+    } finally {
+      setIsSavingStep(false)
+    }
+    setShowPostStepModal(false)
+    await handleInsertCustomStep(pendingCustomStep)
+    setPendingCustomStep(null)
+  }
+
   // Loading state
   if (isLoading) {
     return (
@@ -419,7 +572,7 @@ export function ProceduralNavigationPage() {
           {sidebarOpen && (
             <>
               <StepChecklist
-                steps={steps}
+                steps={runtimeSteps}
                 currentStepIndex={currentStepIndex}
                 completedStepIds={completedStepIds}
                 onStepClick={setCurrentStepIndex}
@@ -458,6 +611,20 @@ export function ProceduralNavigationPage() {
               isLast={currentStepIndex === procedureSteps.length - 1}
             />
           )}
+
+          {/* Add custom step — only on current active incomplete non-custom step */}
+          {currentStep && !completedStepIds.has(currentStep.id) && !('isCustom' in currentStep && currentStep.isCustom) && (
+            <div className="mt-4">
+              <button
+                onClick={() => setShowCustomStepModal(true)}
+                className="flex w-full items-center justify-center gap-2 rounded-lg border border-dashed border-border px-4 py-2.5 text-sm text-muted-foreground transition-colors hover:border-primary/50 hover:text-foreground"
+              >
+                <Plus className="h-4 w-4" />
+                Add Step
+              </button>
+            </div>
+          )}
+
           {session && currentStep && (
             <div className="mt-3 flex justify-end">
               <StepFeedback stepId={currentStep.id} sessionId={session.id} />
@@ -514,6 +681,27 @@ export function ProceduralNavigationPage() {
           </div>
         </div>
       )}
+
+      {/* Custom Step Modal */}
+      <CustomStepModal
+        isOpen={showCustomStepModal}
+        onClose={() => setShowCustomStepModal(false)}
+        onInsertStep={handleStepCreated}
+      />
+
+      {/* Post Step Action Modal */}
+      {pendingCustomStep && (
+        <PostStepActionModal
+          isOpen={showPostStepModal}
+          onClose={() => { setShowPostStepModal(false); setPendingCustomStep(null) }}
+          step={pendingCustomStep}
+          onSaveForLater={handleSaveForLater}
+          onUseNow={handleUseNow}
+          onBoth={handleBoth}
+          isFromLibrary={pendingIsFromLibrary}
+          isSaving={isSavingStep}
+        />
+      )}
     </div>
   )
 }