Add wallet transaction simulation before on-chain submission

[Smartdevs17]

Context

On-chain Soroban transactions (subscription charges, credit transfers, SLA claims) can fail due to insufficient gas, contract state, or auth errors, wasting fees and causing poor UX.

Current Limitation/Problem

Transactions are submitted without simulation. Users pay fees for failed transactions and get cryptic error messages.

Expected Outcome

Pre-submission transaction simulation using Soroban simulation API: validate gas, auth requirements, predicted state changes, and expected results before wallet signature.

Acceptance Criteria

• Simulation endpoint: POST /transactions/simulate returns gas estimate, auth entries, state diff, expected result
• Mobile integration: show simulation result in bottom sheet before wallet signature request (XRPL or Freighter)
• Gas estimation: accurate to within 10% of actual consumption (measured against 100 historical transactions)
• Failure prediction: detect common errors (insufficient balance, expired entry, auth mismatch, contract error) before submission
• Fallthrough: if simulation service unavailable (offline), warn user and skip simulation
• Metrics: simulation success rate, gas accuracy percentage, prediction accuracy (false positive/negative)
• Edge case: simulation succeeds but transaction fails (state changed between simulate and submit)

Technical Scope

• backend/simulation/ - new domain module
• backend/simulation/connectors/ - Soroban RPC simulation client
• mobile/app/services/ - TransactionSimulationService
• mobile/app/components/ - SimulationResultSheet (bottom sheet component)
• contracts/simulation/ - helper contract for dry-run state access

[Auwal007]

@Auwal007 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I can architect the Soroban RPC simulation client inside backend/simulation/connectors/. I'll focus on parsing the dry-run footprint, mapping common host functions/auth mismatches to explicit consumer-facing errors, and calculating the 10% gas headroom. Having built high-fidelity RPC transaction pipelines on Stellar/Soroban before, I'll ensure the backend properly translates raw state footprints into clear failure predictions.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Auwal007 to this issue.

[MorsH14]

@MorsH14 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Id love to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @MorsH14 to this issue.

[drips-wave]

Congratulations, @Auwal007! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @Auwal007: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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