[Wave 9] Add AbortSignal support to announcement streams

[truthixify]

Problem

The public docs describe cancellation, but fetchAnnouncementsStream and its low-level RPC calls do not expose a signal option in the implementation.

Done when

• Accept AbortSignal in stream options.
• Cancel pending RPC requests and parallel chunks.
• Close iterators and release cache work on abort.
• Add tests for abort before the first page and during pagination.

[beebah30]

@beebah30 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hi Maintainer, I’ve reviewed the task and believe I can handle it effectively. I’m available to begin working on the issue and will aim to provide a clean, properly tested solution.

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[official-rex]

@official-rex has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

I’d like to work on this issue. I can add AbortSignal support to the stream options, ensure pending RPCs and parallel chunks are cancelled properly, and add tests covering aborts before the first page and during pagination.

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

[joshuasaleh200-spec]

@joshuasaleh200-spec has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hello Maintener, I've review this issue and I can work on it, please assign it to me.

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[boalambo]

@boalambo has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hello maintainer, I would like to work on this issue

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[aratass]

@aratass has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

The implementation is finished and tested, and I will open the PR as soon as this is assigned. The branch is public if you want to look first: https://github.com/aratass/sdk/tree/feat/issue-200-abort-signal (two commits on develop).

It covers all four points:

• Signal in stream options: signal on FetchAnnouncementsOptions, and also on scanAnnouncementsStream and RpcClient.request() (the low-level RPC path). Aborts reject with signal.reason, like fetch().
• Pending RPC requests and parallel chunks: every Soroban and Horizon call gets the signal, and the parallel chunks share one linked signal. An abort is never counted as an endpoint failure or failover, and retry backoff is cancelled too.
• Iterators and cached work: iterators close, and the pipeline read-ahead, mergeOrdered heads and the dedupe set are released.
• Tests: abort before the first page and during pagination, sequential and parallel. There are 29 new tests, and most fail on develop.

While testing I found that breaking out of scanAnnouncementsStream while its read-ahead window is full hangs forever on develop, because the pump stays parked waiting for space. The branch fixes that and adds a regression test.

format:check, build, api:check, test (1250 passing) and size all pass locally.

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[drips-wave]

Congratulations, @official-rex! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on September 30, 2026.

🧑‍💻 @official-rex: 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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