diff --git a/frontend/docs/FRAUD_DETECTION.md b/frontend/docs/FRAUD_DETECTION.md
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+# Fraud Detection System Guide (Backend + ML)
+
+## Overview
+
+The fraud detection system is a **cross-service pipeline** involving:
+
+- Backend API (request orchestration + storage)
+- Fraud Detection Service (rules + orchestration layer)
+- ML Microservice (model inference + scoring)
+- Feedback loop (retraining system)
+
+This document explains the **full lifecycle of fraud analysis**.
+
+---
+
+## 1. Fraud Detection Flow
+
+### Step-by-step pipeline:
+
+1. Backend receives transaction/event
+2. Backend forwards payload to fraud-detection service
+3. Fraud service calls ML microservice for scoring
+4. ML service returns risk score + explanation
+5. Backend evaluates thresholds
+6. Alert is created if risk is high
+7. Result is stored in database
+8. User/admin feedback is collected later
+9. Feedback is used for retraining
+
+---
+
+## 2. API Request Flow
+
+### Backend Entry Point
diff --git a/frontend/docs/SEARCH.md b/frontend/docs/SEARCH.md
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+# Search System Behavior Guide
+
+## Overview
+
+The search system supports multiple ranking and retrieval strategies depending on database capabilities and query type. It is designed to gracefully degrade when advanced features are unavailable.
+
+---
+
+## 1. Feature Detection Model
+
+At runtime, the search service detects available database capabilities:
+
+### Supported features:
+- Full Text Search (FTS)
+- Trigram similarity (pg_trgm)
+- Basic ILIKE fallback
+
+### Detection order:
+1. Check if FTS indexes exist
+2. Check if trigram extension is enabled
+3. Fall back to basic LIKE queries
+
+---
+
+## 2. Query Execution Strategy
+
+Search execution follows a layered approach:
+
+### Layer 1 — Full Text Search (Primary)
+Used when FTS is available.
+
+- Uses `to_tsvector`
+- Ranked using `ts_rank`
+- Best performance + semantic matching
+
+---
+
+### Layer 2 — Trigram Similarity (Secondary)
+Used when FTS is unavailable or insufficient.
+
+- Uses `similarity(column, query)`
+- Requires `pg_trgm`
+- Handles typos and fuzzy matching
+
+---
+
+### Layer 3 — Fallback LIKE Search (Last Resort)
+
+Used when no advanced DB features are available.
+
+- Uses `ILIKE '%query%'`
+- No ranking intelligence
+- Lowest performance and relevance
+
+---
+
+## 3. Ranking Model
+
+When multiple strategies are active, results are merged and ranked using:
+
+Priority order:
+1. FTS rank score (highest weight)
+2. Trigram similarity score
+3. Relevance boost (exact match in title/name)
+4. Recency boost (if timestamp exists)
+
+Final score is normalized before sorting.
+
+---
+
+## 4. Pagination Model (Cursor-Based)
+
+Search uses cursor pagination, not offset pagination.
+
+### Request parameters:
+- `limit` → number of results per page
+- `cursor` → last seen result identifier
+
+### How cursor works:
+- Cursor stores `(score, id)` pair
+- Next query uses:
+  - `WHERE (score, id) < cursor`
+  - ordered by `(score DESC, id DESC)`
+
+### Benefits:
+- Stable pagination under inserts
+- No duplicates across pages
+- Better performance than OFFSET
+
+---
+
+## 5. Fallback Behavior Summary
+
+| Capability Missing | System Behavior |
+|--------------------|-----------------|
+| FTS disabled       | Switch to trigram |
+| Trigram disabled   | Switch to LIKE |
+| No indexes         | Full table scan (last resort) |
+
+---
+
+## 6. Query Degradation Rules
+
+When performance constraints exist:
+
+- Reduce ranking complexity
+- Skip trigram scoring
+- Limit result set early
+- Prefer indexed columns only
+
+---
+
+## 7. DTO Contract Alignment
+
+Search DTO supports:
+
+- `query: string`
+- `limit?: number`
+- `cursor?: string`
+- `filters?: object`
+
+Validation ensures:
+- limit max cap enforced
+- cursor format validated
+- empty query rejected
+
+---
+
+## 8. Validation Source of Truth
+
+This document aligns with:
+
+- `backend/src/search/search.service.ts`
+- Search DTO definitions
+- Database index configuration
+
+---
+
+## 9. Notes for Frontend Consumers
+
+- Always treat results as **ranked, not ordered by insertion**
+- Do not assume stable ordering without cursor usage
+- Cursor must be treated as opaque string
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diff --git a/frontend/docs/deployment.md b/frontend/docs/deployment.md
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+## Fraud Detection System Deployment
+
+The fraud detection system consists of:
+
+### Services:
+- Backend API (Node/NestJS)
+- Fraud Detection Service (internal module)
+- ML Microservice (Python/FastAPI or similar)
+
+---
+
+### Dependency Flow:
+
+Backend → Fraud Service → ML Service
+
+---
+
+### Critical Requirements:
+
+- ML service must be deployed before enabling fraud scoring
+- Timeout fallback must be enabled in backend
+- Feature flags control:
+  - enableFraudDetection
+  - enableMLScoring
+
+---
+
+### Failure Handling:
+
+If ML service is down:
+- system falls back to rule engine
+- alerts still generated in degraded mode
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diff --git a/frontend/src/components/usePaymentCheckout.ts b/frontend/src/components/usePaymentCheckout.ts
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+++ b/frontend/src/components/usePaymentCheckout.ts
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+import { useState } from "react";
+
+type CheckoutParams = {
+  amount: number;
+  splitId: string;
+};
+
+export const usePaymentCheckout = () => {
+  const [loading, setLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+  const [lastSubmittedId, setLastSubmittedId] = useState<string | null>(null);
+
+  const isWalletConnected = () => {
+    // replace with real wallet hook
+    return Boolean(window?.ethereum?.selectedAddress);
+  };
+
+  const isCorrectNetwork = () => {
+    // replace with real chain check
+    return true;
+  };
+
+  const submitPayment = async (params: CheckoutParams) => {
+    const { splitId } = params;
+
+    // 🚫 prevent duplicate submits
+    if (loading || lastSubmittedId === splitId) return;
+
+    setError(null);
+
+    if (!isWalletConnected()) {
+      setError("Wallet not connected");
+      return;
+    }
+
+    if (!isCorrectNetwork()) {
+      setError("Wrong network");
+      return;
+    }
+
+    try {
+      setLoading(true);
+      setLastSubmittedId(splitId);
+
+      // simulate payment request
+      await new Promise((res) => setTimeout(res, 1000));
+
+      // replace with real API call
+      console.log("Payment successful for split:", splitId);
+    } catch (e: any) {
+      setError(e.message || "Payment failed");
+    } finally {
+      setLoading(false);
+    }
+  };
+
+  return {
+    submitPayment,
+    loading,
+    error,
+    isWalletConnected: isWalletConnected(),
+    isCorrectNetwork: isCorrectNetwork(),
+  };
+};
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