fix(batch): retry R2 upload on transient failure in BatchPayloadProcessor

[matt-aitken]

A single "fetch failed" from the object store was aborting the entire batch stream with no retry. Added p-retry (3 attempts, 500ms-2s backoff) around ploadPacketToObjectStore so transient network errors self-heal server-side instead of propagating to the SDK.

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Latest commit: 8046caa

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📥 Commits

Reviewing files that changed from the base of the PR and between 48bd11c and 8046caa.

📒 Files selected for processing (4)

• .server-changes/batch-r2-upload-retry.md
• apps/webapp/app/routes/api.v3.batches.$batchId.items.ts
• apps/webapp/app/runEngine/concerns/batchPayloads.server.ts
• apps/webapp/test/engine/batchPayloads.test.ts

✅ Files skipped from review due to trivial changes (3)

• apps/webapp/app/routes/api.v3.batches.$batchId.items.ts
• apps/webapp/test/engine/batchPayloads.test.ts
• .server-changes/batch-r2-upload-retry.md

🚧 Files skipped from review as they are similar to previous changes (1)

• apps/webapp/app/runEngine/concerns/batchPayloads.server.ts

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Walkthrough

This pull request adds retry handling for transient object-store upload failures in batch processing: BatchPayloadProcessor.process() now retries uploadPacketToObjectStore using p-retry with 3 attempts and exponential backoff (500ms–2s). The batch items route no longer sets an x-should-retry: false header on 500 responses. A new Vitest test suite verifies offload success, retry behavior, terminal failure after retries, and the no-offload case. Documentation describing the change was also added.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Explanation

Changes touch four areas: a small route handler header removal, the batch payload processor (adds retried upload with logging and backoff), a comprehensive test file with four scenarios, and a documentation file. The edits are focused on a single feature but include moderate new logic and test coverage requiring separate verification of retry semantics, logging, and test mocks.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The PR description is minimal but clearly explains the core issue and solution. However, it does not follow the repository's required template structure, which includes sections for Closes #, Checklist, Testing, Changelog, and Screenshots.	Provide a description that follows the template structure: include issue reference, completed checklist items, testing details, and a changelog entry. The technical details about p-retry configuration should be included in the Changelog section.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'fix(batch): retry R2 upload on transient failure in BatchPayloadProcessor' directly describes the main change: adding retry logic to R2 uploads in the BatchPayloadProcessor, which aligns perfectly with the changeset's primary objective.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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