feat: add basic prediction market

.github/workflows/prediction-market-tests.yml

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+name: Prediction Market Tests
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+    paths:
+      - "prediction_market_contract/**"
+      - ".github/workflows/prediction-market-tests.yml"
+  workflow_dispatch:
+
+jobs:
+  prediction-market-tests:
+    name: Prediction Market Tests
+    runs-on: ubuntu-latest
+    env:
+      AZTEC_ENV: sandbox
+      AZTEC_VERSION: 3.0.0-devnet.4
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v5
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: 1.1.36
+
+      - name: Set up Docker
+        uses: docker/setup-buildx-action@v3
+
+      - name: Install Aztec CLI
+        run: |
+          curl -s https://install.aztec.network > tmp.sh
+          NON_INTERACTIVE=1 bash tmp.sh
+          rm tmp.sh
+
+      - name: Update path
+        run: echo "$HOME/.aztec/bin" >> $GITHUB_PATH
+
+      - name: Set Aztec version and start sandbox
+        run: |
+          aztec-up ${{ env.AZTEC_VERSION }}
+          docker tag aztecprotocol/aztec:${{ env.AZTEC_VERSION }} aztecprotocol/aztec:latest
+          aztec start --sandbox &
+
+      - name: Wait for sandbox to be ready
+        run: |
+          echo "Waiting for sandbox to start..."
+          MAX_RETRIES=60
+          for i in $(seq 1 $MAX_RETRIES); do
+            if curl -s http://localhost:8080/status >/dev/null 2>&1; then
+              echo "Sandbox is ready!"
+              break
+            fi
+            if [ $i -eq $MAX_RETRIES ]; then
+              echo "Sandbox failed to start after $MAX_RETRIES attempts"
+              exit 1
+            fi
+            echo "Waiting... ($i/$MAX_RETRIES)"
+            sleep 2
+          done
+
+      - name: Install project dependencies
+        working-directory: prediction_market_contract
+        run: bun install
+
+      - name: Run Noir unit tests
+        working-directory: prediction_market_contract
+        run: aztec test
+        timeout-minutes: 10
+
+      - name: Compile contract and generate artifacts
+        working-directory: prediction_market_contract
+        run: |
+          aztec-nargo compile
+          aztec-postprocess-contract
+          aztec codegen target -o artifacts
+
+      - name: Run end-to-end tests
+        working-directory: prediction_market_contract
+        run: bun test
+        timeout-minutes: 15
+
+      - name: Upload test results if failed
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: test-logs
+          path: |
+            prediction_market_contract/tests/**/*.log
+          retention-days: 7
+
+      - name: Cleanup
+        if: always()
+        run: |
+          echo "Stopping Aztec sandbox..."
+          pkill -f "aztec" || true
+          docker stop $(docker ps -q) || true
+          docker rm $(docker ps -a -q) || true

prediction_market_contract/.gitignore

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+target/
+artifacts/
+node_modules/
+dist/
+*.log
+.DS_Store

prediction_market_contract/Nargo.toml

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+[package]
+name = "prediction_market_contract"
+authors = [""]
+compiler_version = ">=0.25.0"
+type = "contract"
+
+[dependencies]
+aztec = { git = "https://github.com/AztecProtocol/aztec-packages/", tag = "v3.0.0-devnet.4", directory = "noir-projects/aztec-nr/aztec" }
+uint_note = { git = "https://github.com/AztecProtocol/aztec-packages/", tag = "v3.0.0-devnet.4", directory = "noir-projects/aztec-nr/uint-note" }

prediction_market_contract/README.md

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+# Prediction Market Contract
+
+A prediction market implementation on Aztec using a **Constant Sum Market Maker (CSMM)** for binary outcomes with **full identity privacy**.
+
+## Overview
+
+This contract allows users to:
+- **Vote on binary outcomes** (YES/NO) **anonymously** - no one knows WHO voted
+- **Hold fully private balances** - collateral and share holdings are all hidden
+- **Experience dynamic pricing** that adjusts based on market sentiment
+- **Get slippage protection** to prevent adverse price movements
+- **Single-transaction voting** using partial notes pattern
+
+## Privacy Model
+
+### What's Private
+
+| Data | Privacy | Notes |
+|------|---------|-------|
+| Voter identity | **PRIVATE** | Public function doesn't receive sender address |
+| Collateral balances | **PRIVATE** | Stored as private notes (UintNote) |
+| Share balances | **PRIVATE** | Stored as private notes (UintNote) |
+| Your vote (YES/NO) | **PRIVATE** | Hidden via partial notes |
+
+### What's Public
+
+| Data | Visibility | Why |
+|------|------------|-----|
+| Price changes | PUBLIC | Necessary for AMM pricing |
+| Trade amounts | PUBLIC | Affects price movement |
+| That someone bought YES/NO | PUBLIC | Observable from price changes |
+
+### Privacy Architecture
+
+The contract uses **partial notes** for private voting (like the [AMM contract](https://github.com/AztecProtocol/aztec-packages/tree/master/noir-projects/noir-contracts/contracts/amm_contract)):
+
+```
+1. buy_outcome() [PRIVATE]
+   |
+   +-- Consumes private collateral notes
+   +-- Creates change note if needed
+   +-- Creates partial note commitment (hides owner)
+   +-- Enqueues public call WITHOUT sender address
+   v
+2. _process_buy() [PUBLIC]
+   |
+   +-- Calculates shares based on CSMM pricing
+   +-- Updates YES/NO supplies (price changes)
+   +-- Completes partial note with share amount
+   v
+   Shares appear in user's private balance (single tx!)
+```
+
+Key privacy feature: The public `_process_buy()` function **does not receive the sender address**. It only knows WHAT was traded, not WHO traded.
+
+## Usage
+
+### Voting Flow (Single Transaction)
+
+```typescript
+// Deposit collateral privately
+await market.methods.deposit(1000n).send({ from: myAddress }).wait()
+
+// Buy outcome privately - single transaction!
+await market.methods.buy_outcome(
+  true,    // is_yes
+  500n,    // collateral_amount
+  900n,    // min_shares_out (slippage protection)
+).send({ from: myAddress }).wait()
+
+// Your shares are immediately in your private balance!
+const myBalance = await market.methods.get_yes_balance(myAddress).simulate({ from: myAddress })
+```
+
+### Collateral Management (All Private)
+
+```typescript
+// Deposit collateral (private)
+await market.methods.deposit(1000n).send({ from: myAddress }).wait()
+
+// Withdraw collateral (private)
+await market.methods.withdraw(500n).send({ from: myAddress }).wait()
+
+// Check balance (view private notes)
+const balance = await market.methods.get_collateral_balance(myAddress).simulate({ from: myAddress })
+```
+
+## Development
+
+### Prerequisites
+
+```bash
+# Install Aztec tools
+bash -i <(curl -s https://install.aztec.network)
+aztec-up 3.0.0-devnet.4
+
+# Install npm dependencies
+npm install
+```
+
+### Building
+
+```bash
+# Compile the contract
+aztec-nargo compile
+
+# Post-process and generate TypeScript bindings
+aztec-postprocess-contract
+aztec codegen target -o artifacts
+```
+
+### Testing
+
+#### Noir Unit Tests
+
+```bash
+aztec test
+```
+
+Tests the CSMM pricing functions:
+- Share calculations at various price points
+- Price calculations and invariants
+- Edge cases
+
+#### End-to-End Tests
+
+```bash
+# Start Aztec sandbox (in separate terminal)
+aztec start --sandbox
+
+# Run tests
+npm test
+```
+
+Tests the full private voting flow:
+- Contract deployment
+- Private deposit/withdraw
+- Private buy_outcome (single tx with partial notes)
+- Price movements
+- Balance privacy
+
+## Constant Sum Market Maker (CSMM)
+
+### Core Invariant
+```
+price_YES + price_NO = 1
+```
+
+### Pricing Formula
+```
+price_YES = yes_supply / (yes_supply + no_supply)
+shares_out = collateral_in / current_price
+```
+
+### Example
+
+```
+Initial: YES=5000, NO=5000, price_YES=50%
+
+Alice buys 1000 collateral of YES:
+- Shares received: 1000 / 0.50 = 2000 YES
+- New YES supply: 7000
+- New price_YES: 7000 / 12000 = 58.3%
+```