diff --git a/frontend/src/components/MilestoneBuilder.tsx b/frontend/src/components/MilestoneBuilder.tsx
index f6b4590..859ed2d 100644
--- a/frontend/src/components/MilestoneBuilder.tsx
+++ b/frontend/src/components/MilestoneBuilder.tsx
@@ -1,4 +1,4 @@
-import { useState } from 'react'
+import { useState, useMemo } from 'react'
 
 export interface MilestoneInput {
   amount: string
@@ -8,10 +8,54 @@ export interface MilestoneInput {
 interface MilestoneBuilderProps {
   milestones: MilestoneInput[]
   onChange: (milestones: MilestoneInput[]) => void
+  onValidationChange?: (isValid: boolean) => void
 }
 
-export default function MilestoneBuilder({ milestones, onChange }: MilestoneBuilderProps) {
+export default function MilestoneBuilder({ milestones, onChange, onValidationChange }: MilestoneBuilderProps) {
   const [errors, setErrors] = useState<Record<number, string>>({})
+  const [duplicates, setDuplicates] = useState<Set<number>>(new Set())
+
+  // Check for duplicate amounts and invalid values
+  const validationStatus = useMemo(() => {
+    const amountMap = new Map<string, number[]>()
+    const newDuplicates = new Set<number>()
+    let hasErrors = false
+
+    milestones.forEach((milestone, index) => {
+      const numValue = parseFloat(milestone.amount)
+
+      // Check for individual validation errors
+      if (milestone.amount && (isNaN(numValue) || numValue <= 0)) {
+        hasErrors = true
+      }
+
+      // Track amounts for duplicate detection
+      if (milestone.amount && !isNaN(numValue) && numValue > 0) {
+        const key = numValue.toString()
+        if (!amountMap.has(key)) {
+          amountMap.set(key, [])
+        }
+        amountMap.get(key)!.push(index)
+      }
+    })
+
+    // Mark duplicates
+    amountMap.forEach((indices) => {
+      if (indices.length > 1) {
+        indices.forEach(index => newDuplicates.add(index))
+        hasErrors = true
+      }
+    })
+
+    setDuplicates(newDuplicates)
+    const isValid = !hasErrors && milestones.length > 0 && milestones.every(m => m.amount.trim() !== '')
+
+    if (onValidationChange) {
+      onValidationChange(isValid)
+    }
+
+    return { isValid, hasErrors }
+  }, [milestones, onValidationChange])
 
   const addMilestone = () => {
     onChange([...milestones, { amount: '', description: '' }])
@@ -141,6 +185,9 @@ export default function MilestoneBuilder({ milestones, onChange }: MilestoneBuil
               {errors[index] && (
                 <p className="mt-1 text-xs text-red-400">{errors[index]}</p>
               )}
+              {duplicates.has(index) && !errors[index] && (
+                <p className="mt-1 text-xs text-amber-400">⚠️ This amount is duplicated in another milestone</p>
+              )}
             </div>
 
             <div>
diff --git a/frontend/src/hooks/useAgreementEvents.ts b/frontend/src/hooks/useAgreementEvents.ts
index 0240027..acacbc7 100644
--- a/frontend/src/hooks/useAgreementEvents.ts
+++ b/frontend/src/hooks/useAgreementEvents.ts
@@ -49,8 +49,11 @@ export function useAgreementEvents(agreementId: string | null) {
     async (signal: AbortSignal): Promise<boolean> => {
       if (!agreementId) return true // treat no-id as "success" (no-op)
 
-      setIsLoading(true)
-      setError(null)
+      // Guard state updates for unmounted components
+      if (!unmountedRef.current) {
+        setIsLoading(true)
+        setError(null)
+      }
 
       // Combine the caller's signal with a per-request timeout signal.
       const timeoutId = setTimeout(() => {
diff --git a/frontend/src/hooks/useCountUp.ts b/frontend/src/hooks/useCountUp.ts
index 3843266..48ef118 100644
--- a/frontend/src/hooks/useCountUp.ts
+++ b/frontend/src/hooks/useCountUp.ts
@@ -11,38 +11,52 @@ export function useCountUp(
 ): number {
   const { duration = 500, minThreshold = 5 } = options
 
-  const [displayValue, setDisplayValue] = useState(targetValue)
-  const previousValueRef = useRef(targetValue)
+  // Validate and clamp target value
+  const validatedTarget = validateAndClampTarget(targetValue)
+
+  const [displayValue, setDisplayValue] = useState(validatedTarget)
+  const previousValueRef = useRef(validatedTarget)
   const animationFrameRef = useRef<number | null>(null)
   const startTimeRef = useRef<number | null>(null)
+  const iterationCountRef = useRef(0)
 
   useEffect(() => {
     const startValue = previousValueRef.current
-    const change = Math.abs(targetValue - startValue)
+    const change = Math.abs(validatedTarget - startValue)
 
     if (change === 0) return
 
     if (change < minThreshold) {
-      setDisplayValue(targetValue)
-      previousValueRef.current = targetValue
+      setDisplayValue(validatedTarget)
+      previousValueRef.current = validatedTarget
       return
     }
 
     const startTime = performance.now()
     startTimeRef.current = startTime
+    iterationCountRef.current = 0
 
     const animate = (currentTime: number) => {
+      // Safeguard against infinite animation loops (max 1000 iterations)
+      iterationCountRef.current += 1
+      if (iterationCountRef.current > 1000) {
+        setDisplayValue(validatedTarget)
+        previousValueRef.current = validatedTarget
+        animationFrameRef.current = null
+        return
+      }
+
       const elapsed = currentTime - startTime
       const progress = Math.min(elapsed / duration, 1)
 
-      const current = startValue + (targetValue - startValue) * progress
+      const current = startValue + (validatedTarget - startValue) * progress
       setDisplayValue(Math.round(current))
 
       if (progress < 1) {
         animationFrameRef.current = requestAnimationFrame(animate)
       } else {
-        setDisplayValue(targetValue)
-        previousValueRef.current = targetValue
+        setDisplayValue(validatedTarget)
+        previousValueRef.current = validatedTarget
         animationFrameRef.current = null
       }
     }
@@ -55,7 +69,30 @@ export function useCountUp(
         animationFrameRef.current = null
       }
     }
-  }, [targetValue, duration, minThreshold])
+  }, [validatedTarget, duration, minThreshold])
 
   return displayValue
 }
+
+/**
+ * Validates and clamps the target value for count-up animation.
+ *
+ * Ensures:
+ * - Input is a finite number (rejects NaN and Infinity)
+ * - Value is within reasonable range [0, 1e9]
+ * - Returns a safe default (0) for invalid inputs
+ *
+ * @param value - The target value to validate
+ * @returns A valid, finite number within the safe range
+ */
+function validateAndClampTarget(value: number): number {
+  // Check if value is a finite number
+  if (!Number.isFinite(value)) {
+    return 0
+  }
+
+  // Clamp to safe range [0, 1e9]
+  const MIN_VALUE = 0
+  const MAX_VALUE = 1e9
+  return Math.max(MIN_VALUE, Math.min(MAX_VALUE, value))
+}
diff --git a/frontend/src/hooks/useStellarStatus.ts b/frontend/src/hooks/useStellarStatus.ts
index f966001..2dc81fe 100644
--- a/frontend/src/hooks/useStellarStatus.ts
+++ b/frontend/src/hooks/useStellarStatus.ts
@@ -1,5 +1,6 @@
 import { useState, useEffect } from 'react'
 import { RPC_URL } from '../lib/config'
+import { createAbortSignalWithTimeout } from '../lib/abort'
 
 type NetworkStatus = 'online' | 'degraded' | 'offline' | 'checking'
 
@@ -28,7 +29,7 @@ export function useStellarStatus(intervalMs = 60000): StellarStatus {
           method: 'getHealth',
           params: [],
         }),
-        signal: AbortSignal.timeout(5000),
+        signal: createAbortSignalWithTimeout(5000),
       })
 
       const latency = Date.now() - start
diff --git a/frontend/src/lib/abort.ts b/frontend/src/lib/abort.ts
new file mode 100644
index 0000000..65ca86b
--- /dev/null
+++ b/frontend/src/lib/abort.ts
@@ -0,0 +1,38 @@
+/**
+ * Creates an AbortSignal that automatically aborts after the specified timeout.
+ * Provides a fallback for browsers that don't support AbortSignal.timeout().
+ *
+ * @param timeoutMs - The timeout in milliseconds
+ * @returns An AbortSignal that aborts after the specified timeout
+ */
+export function createAbortSignalWithTimeout(timeoutMs: number): AbortSignal {
+  // Check if AbortSignal.timeout is supported (Chrome 103+, Safari 15.4+, etc.)
+  if (typeof AbortSignal !== 'undefined' && 'timeout' in AbortSignal) {
+    try {
+      return AbortSignal.timeout(timeoutMs)
+    } catch {
+      // Fallback if native implementation fails
+      return createAbortSignalFallback(timeoutMs)
+    }
+  }
+
+  // Fallback for older browsers
+  return createAbortSignalFallback(timeoutMs)
+}
+
+/**
+ * Fallback implementation using AbortController and setTimeout.
+ * Works on all browsers that support AbortController.
+ */
+function createAbortSignalFallback(timeoutMs: number): AbortSignal {
+  const controller = new AbortController()
+  const timeoutId = setTimeout(() => {
+    controller.abort()
+  }, timeoutMs)
+
+  // Store the timeoutId on the signal so it can be cleaned up if needed
+  const signal = controller.signal as any
+  signal._timeoutId = timeoutId
+
+  return signal
+}