feat(TransactionPanel): defaultDestination/Amount/Memo props, onSuccess/onError callbacks, 28-char memo counter

[k-deejah]

Problem

1. TransactionPanel does not support a defaultDestination or defaultAmount prop — consumers embedding TransactionPanel in a "Pay X" flow (e.g. a donation button) have no way to pre-fill the form fields.

2. TransactionPanel does not emit an onSuccess callback with the TxResult — after submission, setResult(data) updates internal state but no external callback fires. Consumers building automated workflows have no way to react to a successful payment.

3. TransactionPanel memo field has no character count indicator — Stellar text memos are limited to 28 bytes. Users typing long memos do not see the limit until they hit it or the transaction fails.

Solution

1. Add defaultDestination?: string, defaultAmount?: string, defaultMemo?: string props initializing the form state.
2. Add onSuccess?: (result: TxResult) => void and onError?: (error: string) => void callback props.
3. Add a character counter label below the memo input: {memo.length}/28 with red colour when at/above 28.

Acceptance Criteria

• Default props pre-fill the respective form fields
• onSuccess fires with TxResult after a successful submission
• onError fires with the error string on failure
• Memo counter shows {n}/28 with red colour at/above limit
• npm run build passes

---

Note for Contributors: Write a clear PR description. Include a screenshot of the memo counter at the 28-char limit.

[AvatarMiiDe]

@AvatarMiiDe has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello,
I have reviewed the issue and I am fully equipped to deliver on time. Assign it to me now so I can resolve it.

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

[AbuJulaybeeb]

@AbuJulaybeeb has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi Maintainer, haven reviewed the description of the issue, and well experienced with Js Library,
I would like to hop on the issue and sure to deliver at ETA 2hrs

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

[oluebubejoy]

@oluebubejoy has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Please assign this issue to me

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

[drips-wave]

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

🧑‍💻 @oluebubejoy: 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.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

This issue has been completed by @oluebubejoy as part of the Stellar Wave Program's 7th Wave 🥳

😎 @oluebubejoy: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.