Enforce strict type validation on all XDR-decoded inputs to prevent malformed data from reaching contract logic

[Chuks-coderr]

Description

Add explicit type-validation guards at each entry point's parameter boundary that reject inputs which decode from XDR but contain semantically invalid values such as negative durations, zero rates on non-zero deposits, or asset codes longer than allowed. Each guard should return a typed error variant rather than panicking or allowing the invalid value into business logic.

Acceptance Criteria

• Feature is fully implemented
• Tests pass
• Lint/type checks pass
• PR references this issue number

Notes

⚠️ Do not begin coding until you have been assigned by the maintainer.
Branch as feat/522-security-xdr-input-validation where N is this issue number.

[vijay11149]

@vijay11149 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

i will love to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @vijay11149 to this issue.

[ZeePearl56]

@ZeePearl56 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I would like to work on this issue.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ZeePearl56 to this issue.

[sandrawillow001-afk]

@sandrawillow001-afk has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

sir i will love to work on this issue sir

ℹ️ Repo Maintainers: To accept this application, review their application or assign @sandrawillow001-afk to this issue.

[drips-wave]

Congratulations, @sandrawillow001-afk! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @sandrawillow001-afk: 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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