core: implement transaction-status tracking and reconciliation for payments

[EmeditWeb]

Problem

After a learner signs and submits a transaction there is no reliable tracking
of its on-chain resolution. loans.store.ts has no persistence (#38), so
simulatedAmount, cached loans, and any pending payment are lost on restart.
If a repayment is submitted while the app is backgrounded or killed, it
disappears from the UI with no way to recover its status. There is no pending
-transaction queue, no status polling, and no reconciliation on resume.

Before Starting

Read ALL of these before writing any code:

• context/architecture-context.md
• context/code-standards.md

What To Build

A durable transaction-tracking layer:

1. A persisted pending-transaction queue (Zustand persist / secure storage)
   recording each submitted tx hash, type, and target loan.
2. Background/foreground status polling against the API until each tx reaches
   a terminal state (confirmed / failed / expired), with exponential backoff.
3. Reconciliation on app resume: re-check any still-pending tx and update loan
   state accordingly, surfacing success/failure to the user.
4. Idempotent updates so a tx confirmed while offline is not double-counted.

Files To Touch

• stores/loans.store.ts (persistence)
• src/transactions/* (pending queue + poller)
• services/transactions.service.ts
• relevant screens (pending/confirmed/failed UI)

Acceptance Criteria

• Submitted transactions persist across restart and background/kill
• Status polled to a terminal state with backoff
• Pending txs reconciled on app resume and reflected in loan state
• Updates idempotent; no double-counting on reconnect
• Success/failure surfaced to the user; tests cover queue + reconciliation

Mandatory Checks Before Opening PR

• All context/ files read and understood
• npx expo export --platform web passes
• No TypeScript errors
• No hardcoded hex colors (constants/colors.ts only)
• Icons from lucide-react-native only
• Loading, error, and empty states handled
• PR references this issue number

[julianvillalba688]

Hi team,

I would love to take on this issue. Here is a brief summary of my experience and how I plan to approach implementing durable transaction tracking and reconciliation for StepFi:

My Experience
As a developer experienced in building robust full-stack and mobile infrastructure, I regularly work with state persistence and asynchronous lifecycle synchronization. I have deep experience managing complex state flows with Zustand (including middleware like persist), handling idempotent database and state updates, and structuring API polling systems with exponential backoff to handle unstable network environments gracefully.

Proposed Approach
Durable Persistence Layer: I will update stores/loans.store.ts using Zustand's persistence middleware (integrating secure storage where sensitive/required) to ensure simulatedAmount, cached loans, and pending tx hashes survive app restarts and hard kills.

Transaction Queue & Polling Engine (src/transactions/*): I'll create a dedicated pending-transaction queue. Once a transaction hash is generated, it will enter this persistent queue. A polling service will monitor the hashes against services/transactions.service.ts using an exponential backoff strategy until a terminal state (confirmed, failed, or expired) is reached.

Lifecycle Reconciliation: I will hook into the app’s background/foreground lifecycle to automatically trigger a reconciliation sweep on app resume, re-verifying any outstanding pending transactions.

Idempotency & UI/UX: I will ensure all state updates are strictly idempotent to avoid double-counting. I'll also implement clean loading, error, and empty states on the relevant screens using only lucide-react-native for iconography and constants/colors.ts for styling.

I will strictly adhere to context/architecture-context.md and context/code-standards.md, and ensure npx expo export --platform web passes with zero TypeScript errors before opening the PR.

Looking forward to contributing!

[mubking]

Please u would like to work on this issue

[Exploit34]

Hi maintainer, please let me handle this issue.

[Joyyyb]

​Hi team,
​I’d like to take this on. I can implement the state persistence and transaction tracking missing in loans.store.ts to ensure pending payments aren't lost on restart or backgrounding.
​I will review the architecture and code standards files before diving into the code. I'm ready to get started!

​Best,
Joyyyb