fix(sync): preserve prototype-named canonical payload keys

[rudycelekli]

Summary

Canonical serialization assigned arbitrary JSON keys into a regular object. A metadata key named __proto__ was silently dropped, so distinct payloads produced the same canonical bytes and hash. Build the normalized object without a prototype so JSON keys survive recursively.

Verification

• Bun 1.4.2: tests/worker/sync/canonical-prototype-keys.test.ts tests/worker/sync/canonical-content.test.ts
• 2 regressions fail before; 8 tests / 202 assertions pass after, including shared canonical byte/hash vectors.
• Owned temporary fixtures; no installed plugin or user memory was accessed.
• Source and regression tests only; generated release bundles are unchanged. Hosted CI is not yet reported for this unpublished branch.

AI assistance was used to investigate, implement and verify this change.

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Fixes payload serialization to preserve special property names.

No outstanding findings block merging.

Summary

The client and both sync servers now preserve own JSON keys named __proto__ during canonical serialization. The previously reported server mismatch is fixed.

_{Reviews (2) · Last reviewed commit: "fix(sync): align server canonicalizers f..."}