Respect the DynamoDB scan page size

[dajiaohuang]

Change

Set the DynamoDB request limit from pageSize, request one scan response at a time, and cancel the publisher when the FS2 stream ends. The parallel-scan example now passes its configured page size through unchanged.

Validation

Prior DynamoDB compilation and both StreamScanCancellationSuite tests passed: nonpositive pageSize fails through Stream.raiseError, and early take(1) invokes cancel(). The LocalStack page-size/full-result assertion was added; it is not represented as an executed LocalStack acceptance test. This reassessment reuses the delivered focused test evidence; no new test run claimed.

Standard scalafmt was blocked by the existing incompatible import-rewrite configuration; no formatter success claimed.

[Copilot]

Copilot review overview

🟡 Changes recommended

Invalid input bypasses the stream error channel, and publisher cancellation lacks regression coverage.

Review effort: Balanced
Findings: 1 · 1

Open (2)

• Return invalid pageSize errors through the stream error channel · New
• Test publisher cancellation when stream consumption stops early · New

What changed in this PR

Updates DynamoDB scans to honor configured page sizes and cancel publishers when streams end.

Changes:

• Applies pageSize to scan requests.
• Requests one response at a time with backpressure.
• Adds page-size regression coverage and updates the parallel-scan example.

File	Description
DynamoParallelScan.scala	Passes the configured page size unchanged.
StreamScanSpec.scala	Verifies page sizing and complete results.
StreamScan.scala	Enforces request limits, demand, validation, and cancellation.

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[dajiaohuang]

Updated invalid page-size validation to Stream.raiseError and added two tests using an observable publisher subscription: invalid sizes are captured by attempt, and take(1) invokes cancel(). The project compiles and both StreamScanCancellationSuite tests pass with sbt 1.13.0 / Scala 3.3.8. The standard formatting task is blocked by the existing incompatible AsciiSortImports / Imports(sort=original) configuration; I have kept that unrelated config unchanged.

[barryoneill]

@dajiaohuang another good catch. Thanks!

[dajiaohuang]

Thanks! Happy to help.