[PeerX Backlog # 77] Add a Stripe-like pattern: pre-flight validation function

[ameeribro4-sudo]

Problem Statement
Traders get a single error after they sign and submit. UX cost.
A validate_swap_pre_flight(user, from, to, amount, slippage) would
short-circuit invalid intent before signing.

Expected Outcome
A read-only preflight_swap returning Result<(), SwapChecklistError>.

Acceptance Criteria

• Returns struct with: balance_ok, kyc_ok, rate_limit_ok, slippage_ok,
  oracle_fresh_ok, pool_depth_ok.
• Same Rust function shared between validator and post-check.

Files Affected

• peerx-contracts/counter/src/lib.rs, validation.rs.

Dependencies Issue #72.
Difficulty / Effort 🥈 / M
Labels dx, api

[GBOYEE]

Hi team — I'd like to take this on as part of the GrantFox campaign. I'll implement it and open a PR referencing this issue shortly.

[merlik787-droi]

please assign me this issue

[grantfox-oss]

🦊 GrantFox — @merlik787-droi has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #77)
2. Your PR will be reviewed by the OpenPeerX maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@merlik787-droi's PR #114 was approved and merged by @ameeribro4-sudo.

🏆 @merlik787-droi: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (83 total points). Track your full progress on GrantFox.

👏 Great work, @merlik787-droi! Keep contributing to OpenPeerX.