ADE-47: CRR sync drops changes when a changeset batch splits in the middle of a single db_version

[arul28]

Fixes ADE-47

Summary

Describe the change.

What Changed

Key files and behaviors.

Validation

How you tested.

Risks

Anything to watch.

Linked Linear issues

• ADE-47: CRR sync drops changes when a changeset batch splits in the middle of a single db_version - closes on merge

  Open in ADE  ·  ade-47-crr-sync-drops-changes-when-a-changeset-batch-splits-in-the-middle-of-a-single-db-version branch  ·  PR #435

Greptile Summary

This PR fixes ADE-47, where CRR sync silently dropped rows when a changeset batch was cut in the middle of a db_version group. It also removes the prior Math.max(...spread) call that could throw a RangeError on large db_version groups.

• Core fix (syncHostService.ts): Extracts a new exported selectChangesetBatchChunk function that delays the chunk boundary until a db_version transition, ensuring all rows sharing one db_version are sent together. toDbVersion is now tracked directly via lastIncludedDbVersion rather than a spread into Math.max.
• Tests (syncHostService.test.ts): Four new unit tests cover row-limit splitting, byte-limit splitting, 70k-row single-version batches, and empty-changeset advancement.
• Docs: Two doc files receive short prose notes explaining the invariant that rows within a db_version must not be split across separate host batches.

Confidence Score: 4/5

Safe to merge; the core fix is correct and well-tested, with one unreachable fallback branch that can be cleaned up post-merge.

The chunk-selection logic correctly defers breaks to db_version boundaries and tracks the watermark directly via lastIncludedDbVersion. The only issue is a now-unreachable three-line fallback (lines 232–234) that was a safety valve in the old code but can never trigger under the new loop invariant.

apps/ade-cli/src/services/sync/syncHostService.ts — minor dead-code cleanup around the single-row fallback.

Important Files Changed

Filename	Overview
apps/ade-cli/src/services/sync/syncHostService.ts	Extracts chunk-selection logic into the exported selectChangesetBatchChunk function, which fixes the split-db_version bug by deferring the break to the next db_version boundary; contains one unreachable fallback branch (lines 232–234).
apps/ade-cli/src/services/sync/syncHostService.test.ts	Adds four targeted unit tests for selectChangesetBatchChunk covering row-limit splitting, byte-limit splitting, the 70k-row no-spread case, and empty-changeset advancement.
docs/features/sync-and-multi-device/README.md	Adds a short prose paragraph documenting the host-side batching invariant (all rows for a db_version must travel together) to the sync feature overview.
docs/features/sync-and-multi-device/crdt-model.md	Adds a one-sentence note to the CRDT model doc clarifying that the transport must not split rows sharing a db_version across separate batches.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["selectChangesetBatchChunk(changes, fromDbVersion, toDbVersion, maxRows, maxBytes)"] --> B{changes empty?}
    B -- yes --> C{toDbVersion > fromDbVersion?}
    C -- no --> D["return null"]
    C -- yes --> E["return { changes: [], toDbVersion }"]
    B -- no --> F["Iterate over sorted changes"]
    F --> G{chunk.length > 0\nAND new db_version\nAND row/byte limit hit?}
    G -- yes --> H["break — db_version boundary respected"]
    G -- no --> I["push row to chunk\nupdate lastIncludedDbVersion"]
    I --> F
    H --> J["return { changes: chunk, toDbVersion: lastIncludedDbVersion }"]
    I --> J

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Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
apps/ade-cli/src/services/sync/syncHostService.ts:232-236
The fallback at lines 232–234 is unreachable. The loop's break condition requires `chunk.length > 0`, so the first element of `args.changes` is unconditionally pushed on the first iteration — `chunk` can never be empty after the loop when `args.changes` is non-empty.

```suggestion
  if (chunk.length === 0 && args.toDbVersion <= args.fromDbVersion) return null;
```

_{Reviews (5): Last reviewed commit: "fix(sync): keep changeset batches on db ..." | Re-trigger Greptile}

[linear-code]

ADE-47

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
ade	Ignored	Preview	May 30, 2026 7:56am

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📥 Commits

Reviewing files that changed from the base of the PR and between 8dc8834 and 9dccf9e.

⛔ Files ignored due to path filters (2)

• docs/features/sync-and-multi-device/README.md is excluded by !docs/**
• docs/features/sync-and-multi-device/crdt-model.md is excluded by !docs/**

📒 Files selected for processing (2)

• apps/ade-cli/src/services/sync/syncHostService.test.ts
• apps/ade-cli/src/services/sync/syncHostService.ts

✨ Finishing Touches

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• Create PR with unit tests
• Commit unit tests in branch ade-47-crr-sync-drops-changes-when-a-changeset-batch-splits-in-the-middle-of-a-single-db-version

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[arul28]

@copilot review but do not make fixes

[arul28]

@copilot review but do not make fixes

[arul28]

Addressed Greptile review comment 3328291076 by removing the unbounded Math.max spread and adding a 70,000-row same-db_version regression test. @copilot review but do not make fixes

[arul28]

Rebased onto latest origin/main (df86668). @copilot review but do not make fixes

[arul28]

Rebased onto latest origin/main (8dc8834). @copilot review but do not make fixes