[Contracts] top_up_stream resets last_update_time, discarding recipient's already-vested tokens (sender can reclaim them via cancel)

[grantfox-oss]

Telegram (ask questions / claim the issue here first): https://t.me/+DOylgFv1jyJlNzM0

Why this matters

lib.rs:293 sets stream.last_update_time = env.ledger().timestamp() on top-up, but that field is the accrual anchor: calculate_claimable (lib.rs:343) computes elapsed = effective_now - last_update_time, so advancing it to now zeroes all accrued-but-unwithdrawn time. Concrete loss: 1000-token/1000s stream (rate 1); at t=900 recipient has vested 900 unwithdrawn; sender top_up(+100) -> last_update_time=900 -> get_claimable_amount=0; sender cancel_stream at t=901 pays recipient only 1 and refunds 1099 to sender. Recipient loses ~899 already-earned tokens.

Acceptance criteria

• Remove the stream.last_update_time = now assignment in top_up_stream (lib.rs:293) so prior accrued time is preserved
• After create(1000,1000s), advance 900s then top_up(+100): get_claimable_amount must stay ~900, not drop to 0
• Add test: top_up then immediate cancel_stream - recipient receives the pre-top-up accrued amount
• Cover the paused case: top_up on a paused stream must not push last_update_time past paused_at

Files to touch

• contracts/stream_contract/src/lib.rs

Out of scope

• Changing the protocol fee logic
• Frontend/backend top-up wiring

[olaleyeolajide81-sketch]

@olaleyeolajide81-sketch has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would love to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @olaleyeolajide81-sketch to this issue.

[Isihaq123]

@Isihaq123 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hey, i will like to work on this isiues

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Isihaq123 to this issue.

[Oluwasuyi-Timilehin]

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

Hello maintainer, please assign me to this task. i would get started immediately
ETA 1hour

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

[sammycee769]

@sammycee769 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi 👋

I’d like to work on fixing the top_up_stream issue where resetting last_update_time causes previously accrued tokens to be lost.

I’ll remove the assignment that sets last_update_time to the current timestamp during top-up, ensuring already-vested amounts remain claimable. I’ll also add tests to verify that:

• Accrued tokens remain intact after a top-up (e.g., ~900 tokens still claimable after advancing time and topping up)
• A top-up followed by an immediate cancel_stream correctly pays out the previously accrued amount
• The paused stream case does not incorrectly advance last_update_time past paused_at

This will fix a critical edge case where recipients could lose earned funds and align the contract behavior with expected streaming logic ⚖️

ℹ️ Repo Maintainers: To accept this application, review their application or assign @sammycee769 to this issue.

[elcabasa]

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

Hi team,

I would love to take on this issue! Fixing this anchor-shifting bug is highly critical since resetting last_update_time during a top-up inadvertently wipes out a recipient's already-vested tokens and creates a vector for funds to be unfairly reclaimed during a cancel action.

I have analyzed the scenario outlined in contracts/stream_contract/src/lib.rs and am ready to fix the stream state math to meet all your acceptance criteria:

• State Mutation Fix: Remove the incorrect stream.last_update_time = now assignment inside top_up_stream (lib.rs:293) so that the historical accrual anchor is preserved.
• Accrual Continuity: Ensure that topping up an ongoing stream (e.g., advancing 900s on a 1000/1000s stream before a +100 top-up) allows get_claimable_amount to correctly maintain its ~900 token progression instead of dropping to zero.
• Test Coverage: Add integration tests verifying that a top_up followed by an immediate cancel_stream safely payouts the pre-top-up accrued amount to the recipient.
• Edge Case Handling: Account for paused stream mechanics, ensuring that a top-up action on a paused stream does not inadvertently push the last_update_time past the paused_at timestamp metric.

I will keep the PR strictly isolated to this logic and avoid any changes to protocol fees or out-of-scope frontend components. Could you please assign this issue to me? I'll drop a message in the Telegram group as well. Thanks!

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

[samjay8]

@samjay8 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello Boss, I will like to work on thiss.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @samjay8 to this issue.

[drips-wave]

Congratulations, @samjay8! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @samjay8: 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 🌊

[grantfox-oss]

🦊 GrantFox — @samjay8 has been assigned to this issue!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #786)
2. Your PR will be reviewed by the LabsCrypt maintainers

Good luck! Track your progress on GrantFox.