fix: Contract total_value hardcoded to 0 — portfolio value is never computed from real balances

[Uchechukwu-Ekezie]

Problem

The Soroban smart contract's create_portfolio function stores total_value: 0 when a portfolio is created, and nothing ever updates it. The contract doesn't compute the portfolio's actual USD value from token balances and prices — it just leaves it at zero.

In contracts/src/portfolio.rs, when a portfolio is created:

let portfolio = Portfolio {
    id: id.clone(),
    owner: owner.clone(),
    assets: assets.clone(),
    target_allocations: allocations.clone(),
    drift_threshold,
    total_value: 0,  // <-- always zero
    last_rebalance: 0,
    created_at: env.ledger().timestamp(),
    rebalance_cooldown: 86400,
    is_active: true,
};

The deposit function updates portfolio.total_value += amount but amount is the raw token quantity, not a USD value. So if someone deposits 100 XLM and 50 USDC, total_value becomes 150 — which is meaningless since it's mixing units.

The check_rebalance_needed function uses total_value to calculate drift, but since it's always wrong, the drift calculations are unreliable. The backend works around this by computing its own portfolio value, but the on-chain state is fundamentally broken.

Proposed Fix

Option A: Oracle-driven total value (recommended)

Use the Reflector oracle integration (already partially implemented in contracts/src/reflector.rs) to fetch prices and compute total_value in USD whenever a deposit, withdrawal, or rebalance happens.

In deposit():

1. Get the USD price for the deposited asset from Reflector
2. Compute deposit_usd = amount * price / 10^decimals
3. Add to portfolio.total_value

In execute_rebalance():

1. After trades complete, recalculate total_value from all asset balances and their current prices
2. Store the updated value

In withdraw():

1. Get the USD price for the withdrawn asset
2. Subtract withdraw_usd from total_value

Option B: On-demand calculation

Add a calculate_total_value view function that reads all asset balances, queries Reflector for prices, and returns the computed USD value. Don't store it — compute it on demand. This avoids stale values but costs more gas on every read.

Key considerations

• Reflector prices have a staleness threshold (already checked in reflector.rs). If the price feed is stale, the contract should either use the last known price or revert with a clear error.
• USDC has 7 decimals on Stellar, not 6 like on EVM. The conversion math needs to account for different asset decimals.
• The total_value should be stored as an integer in stroops (10^-7 for USDC) to avoid floating-point issues. The current i128 type is fine for this.

Files to modify

• contracts/src/portfolio.rs — update deposit, withdraw, execute_rebalance to compute and store total_value
• contracts/src/reflector.rs — ensure get_price is callable from portfolio functions
• contracts/src/lib.rs — add a get_total_value view function if going with Option B
• contracts/src/test.rs — add tests for total_value computation after deposit, rebalance, and withdrawal

Acceptance Criteria

• total_value reflects actual USD value after a deposit
• total_value is recalculated after a rebalance
• total_value decreases after a withdrawal
• Stale oracle prices are handled gracefully (revert or use last known)
• Multi-asset portfolios compute total value correctly (not mixing raw units)
• Unit tests cover: single asset, multi-asset, stale price, zero balance

References

• Portfolio creation: contracts/src/portfolio.rs
• Reflector integration: contracts/src/reflector.rs
• Types: contracts/src/types.rs
• Related issue (was Compute total_value from actual token balances and prices instead of leaving it hardcoded to 0 #37): compute total_value from actual balances and prices

Affected Area

Smart Contracts

Checklist

• I have searched existing issues and this is not a duplicate

[bobo-24]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. I’ll prioritize this immediately and ensure a reliable solution is delivered as soon as possible. Thank you!