Fix QueryFilter IN/NOT_IN serialization

[leogdion]

…(#192)

The IN and NOT_IN filters were stripping type metadata from list items, causing CloudKit Web Services to reject queries with HTTP 400 errors.

Changes:

• Fix FilterBuilder to use CustomFieldValuePayload preserving types
• Re-enable GUID queries in CelestraCloud ArticleSyncService
• Optimize ArticleCloudKitService to combine filters at query time
• Update tests to reflect server-side filtering behavior

All tests passing: MistKit (311/311), CelestraCloud (115/115)

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 14.27%. Comparing base (df7836e) to head (aa17000).

Additional details and impacted files

@@                Coverage Diff                 @@
##           v1.0.0-alpha.4     #205      +/-   ##
==================================================
- Coverage           14.31%   14.27%   -0.05%     
==================================================
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  Lines                7179     7179              
==================================================
- Hits                 1028     1025       -3     
- Misses               6151     6154       +3     

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swift-6.1-jammy	14.27% <100.00%> (ø)
swift-6.1-noble	14.27% <100.00%> (ø)
swift-6.2-jammy	14.27% <100.00%> (ø)
swift-6.2-noble	14.27% <100.00%> (ø)
swift-6.3-jammynightly	14.23% <100.00%> (-0.05%)	⬇️
swift-6.3-noblenightly	14.27% <100.00%> (ø)

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[claude]

PR Review: Fix QueryFilter IN/NOT_IN serialization (#205)

Summary

This PR fixes a critical bug in the IN and NOT_IN filter operations that was stripping type metadata from list items, causing CloudKit Web Services to reject queries with HTTP 400 errors. The fix enables proper server-side filtering by combining multiple query filters.

---

✅ Code Quality & Best Practices

Strengths:

1. Root Cause Fix: The change in FilterBuilder.swift:188,204 properly preserves type metadata by using CustomFieldValue.CustomFieldValuePayload($0) instead of stripping it with Components.Schemas.FieldValue(from: $0).value
2. Clean Refactoring: Removal of workaround code and comments in ArticleCloudKitService.swift improves code clarity
3. Documentation: Updated comments clearly explain the fix and new capabilities
4. Test Coverage: Tests updated to reflect the corrected behavior with proper assertions

Minor Observations:

1. Type Safety: The fix leverages Swift's type system correctly by using the custom payload wrapper that preserves CloudKit type information
2. Code Organization: Changes follow the project's SwiftLint conventions and file structure

---

🐛 Potential Issues

None identified - The implementation appears solid. However, consider:

1. Edge Cases: While the tests cover basic scenarios, consider adding tests for:

   • Empty list values in IN/NOT_IN filters
   • Mixed type lists (if supported)
   • Very large GUID lists (>150 items) combined with other filters

2. Error Handling: The current implementation doesn't show explicit validation that CloudKit accepts the combined filters. Consider adding integration tests if not already present.

---

⚡ Performance Considerations

Positive Impact:

1. Server-Side Filtering: Moving from in-memory filtering (line 136-138) to query-time filtering significantly improves performance:

   • Reduces network payload (only matching records returned)
   • Eliminates client-side array filtering overhead
   • Better scalability for large feed operations

2. Query Efficiency: Combining filters in a single query is more efficient than:

   • Multiple separate queries
   • Fetching all records and filtering locally
   • Rate limit considerations mentioned in original comments

No Performance Regressions Identified

---

🔒 Security Concerns

Low Risk:

1. Input Validation: The code uses strongly-typed Swift values (FieldValue.string()) which prevents injection attacks
2. Type Safety: The CustomFieldValuePayload wrapper ensures type consistency sent to CloudKit
3. No Direct String Interpolation: Query construction uses typed parameters throughout

Recommendation: None - security posture is good.

---

🧪 Test Coverage

Strengths:

1. Tests properly updated to reflect new behavior (lines 117-133 in test file)
2. Assertions verify both filter count (2 filters) and result correctness
3. Batch testing ensures large GUID lists work correctly

Suggestions:

1. Consider adding a test that explicitly validates the serialized JSON payload contains proper type metadata
2. Add a test for the case where feedRecordName is nil to ensure single-filter behavior still works
3. Integration test with actual CloudKit Web Services (if not already in another test suite)

---

📝 Additional Notes

1. Breaking Change? This appears to be a bug fix, not a breaking API change. Existing code will benefit from the fix without modification.

2. Documentation: The fix references issue CloudKit Web Services QueryFilter.in() returns HTTP 400 'Unexpected input' #192. Consider updating any related documentation or architecture docs about CloudKit query limitations.

3. Migration Path: The PR description mentions all tests passing (311/311 for MistKit, 115/115 for CelestraCloud), which is excellent validation.

4. Comment Cleanup: Good work removing the extensive workaround comments. The new concise comments better explain the actual behavior.

---

✨ Verdict

LGTM - This is a well-executed bug fix with proper test coverage and documentation. The core fix is minimal (2 lines changed in FilterBuilder), which reduces risk. The removal of workaround code and re-enabling of GUID queries demonstrates the fix's effectiveness.

Recommendation: Approve and merge after CI passes.

Code Quality: ⭐⭐⭐⭐⭐ 5/5
Test Coverage: ⭐⭐⭐⭐ 4/5 (minor suggestions above)
Documentation: ⭐⭐⭐⭐⭐ 5/5

Great work fixing this issue! 🎉

[claude]

PR Review: Fix QueryFilter IN/NOT_IN serialization (#205)

Summary

This PR fixes a critical bug (#192) where the IN and NOT_IN query filters were stripping type metadata from list items, causing CloudKit Web Services to reject queries with HTTP 400 errors. The fix changes FilterBuilder to use CustomFieldValuePayload instead of extracting raw values, preserving necessary type information.

---

✅ Code Quality & Best Practices

Strengths

1. Root Cause Fix: The fix correctly addresses the serialization issue by preserving type metadata through CustomFieldValuePayload.
2. Minimal Change: The fix is surgical—only 2 lines changed in FilterBuilder.swift:188 and :204, keeping the change focused and reducing risk.
3. Comprehensive Testing: All tests pass (311/311 MistKit, 115/115 CelestraCloud), demonstrating the fix works end-to-end.
4. Code Cleanup: Appropriately removes workaround code and in-memory filtering that's no longer needed.
5. Good Documentation: PR description clearly explains the issue, changes, and impact.

Minor Concerns

1. Comment Quality: The new comments in ArticleCloudKitService.swift:113-115 could be more concise:

   // Now that issue #192 is fixed, we can combine .in() with other filters.
   // If feedRecordName is specified, we filter at query time for efficiency.

   Suggestion: Remove the second comment as it's evident from the code logic.

---

🐛 Potential Bugs & Issues

Critical

None identified - The fix appears sound and is validated by passing tests.

Minor Observations

1. FilterBuilder.swift:188 & :204 - Consider adding a code comment explaining why CustomFieldValuePayload is necessary:

   // Use CustomFieldValuePayload to preserve type metadata for CloudKit Web Services
   value: .listValue(values.map { CustomFieldValue.CustomFieldValuePayload($0) }),

2. Test Coverage: The test update in ArticleCloudKitService+Query.swift correctly changes expectations, but consider adding a specific regression test:

   • Test IN filter with large array (50+ items) to prevent regression
   • Test IN + EQUALS filter combination explicitly

---

⚡ Performance Considerations

Improvements

1. Query Efficiency: Moving from in-memory filtering to server-side filtering (ArticleCloudKitService.swift:113) significantly improves performance:

   • Reduces network payload (CloudKit only returns matching records)
   • Reduces client-side processing overhead
   • More scalable for large datasets

2. Reduced Code Complexity: Removing the workaround simplifies the code path and reduces CPU cycles.

No Regressions

• The serialization change (CustomFieldValuePayload) has minimal overhead—it's just wrapping values with type information that CloudKit needs anyway.

---

🔒 Security Concerns

None identified - This is a serialization bug fix with no security implications:

• No changes to authentication or authorization
• No exposure of sensitive data
• No changes to input validation (beyond fixing CloudKit query format)

---

🧪 Test Coverage

Excellent Coverage

1. Integration Tests: CelestraCloud tests verify the end-to-end flow with real CloudKit operations.
2. Unit Tests: Test expectations correctly updated to reflect server-side filtering behavior.
3. Regression Prevention: Re-enabling GUID queries in ArticleSyncService provides ongoing validation.

Recommendations

1. Add explicit test case for IN filter with 50+ items (current tests use small arrays).
2. Add explicit test case combining IN with other filters (e.g., EQUALS, LESS_THAN) to document the fixed behavior.
3. Consider parameterized test in CustomFieldValueTests.swift to verify type preservation for all FieldValue types when used in lists.

---

📋 Architectural Considerations

Positive Impacts

1. Type Safety: Using CustomFieldValuePayload maintains stronger type guarantees through the serialization pipeline.
2. Consistency: All filter builders now correctly preserve type metadata, improving overall API reliability.
3. Maintainability: Removing workaround code reduces technical debt and makes the codebase easier to understand.

Alignment with CLAUDE.md

✅ Follows project conventions:

• Modern Swift features (pattern matching, functional mapping)
• Protocol-oriented design (unchanged)
• Clear error handling (CloudKit errors properly surfaced)
• Good logging practices (errors logged appropriately)

---

🎯 Recommendations

High Priority

1. Add regression test for large IN arrays (50+ items) in MistKitTests.
2. Add regression test for combined filters (IN + EQUALS) in MistKitTests.

Medium Priority

1. Consider adding inline comment in FilterBuilder.swift explaining why CustomFieldValuePayload is used instead of extracting .value.
2. Simplify comment in ArticleCloudKitService.swift:114 (remove redundant line about efficiency).

Low Priority

1. Document this issue and fix in release notes / changelog.
2. Consider adding to documentation: limitations/behaviors of IN filter with CloudKit Web Services.

---

✨ Overall Assessment

Verdict: Excellent fix - Ready to merge ✅

This is a high-quality bug fix that:

• Correctly identifies and fixes the root cause
• Maintains backward compatibility
• Improves performance (server-side vs. client-side filtering)
• Has comprehensive test coverage
• Follows project conventions and best practices

The code is clean, focused, and well-tested. The only suggestions are minor enhancements to documentation and test coverage that can be addressed in follow-up PRs if needed.

Great work solving this tricky serialization issue! 🎉

---

References

• Issue CloudKit Web Services QueryFilter.in() returns HTTP 400 'Unexpected input' #192: CloudKit Web Services QueryFilter.in() returns HTTP 400
• CloudKit Web Services API: openapi.yaml
• Related files: FilterBuilder.swift, CustomFieldValue.CustomFieldValuePayload+FieldValue.swift

[claude]

PR Review: Fix QueryFilter IN/NOT_IN serialization

Summary

This PR fixes a critical bug where IN and NOT_IN filters were stripping type metadata from list items, causing CloudKit Web Services to reject queries with HTTP 400 errors. The fix properly preserves type information by using CustomFieldValuePayload instead of extracting raw values.

Code Quality ✅

Strengths:

1. Root Cause Fix: The change in FilterBuilder.swift (lines 188, 204) correctly addresses the type metadata loss by using CustomFieldValue.CustomFieldValuePayload($0) instead of Components.Schemas.FieldValue(from: $0).value

2. Clean Refactoring: The removal of workaround code in ArticleCloudKitService.swift and ArticleSyncService.swift demonstrates that the fix enables proper filter composition

3. Test Updates: Tests have been updated to reflect the correct server-side filtering behavior

4. Documentation: Comments have been updated to reflect the new capability of combining filters

Code Review Notes:

FilterBuilder.swift (Lines 183-192, 199-207):

// BEFORE: Stripped type metadata
value: .listValue(values.map { Components.Schemas.FieldValue(from: $0).value })

// AFTER: Preserves type metadata  
value: .listValue(values.map { CustomFieldValue.CustomFieldValuePayload($0) })

This is the correct fix. The old code was calling .value on the FieldValue, which extracted only the payload and lost the type information. The new approach maintains the full type-wrapped payload structure that CloudKit Web Services expects.

Potential Issues ⚠️

1. Test Coverage Gap

The existing FilterBuilderTests.swift tests IN/NOT_IN filters but only validates structure (comparator, fieldName, type). There are no tests that verify the actual serialization output or that type metadata is preserved in the JSON payload sent to CloudKit.

Recommendation: Add integration tests that serialize IN filters and verify the JSON structure includes type information for each list element:

@Test("IN filter preserves type metadata in serialization")
func inFilterSerializesWithTypes() throws {
  let filter = FilterBuilder.in("guids", [.string("abc"), .string("def")])
  let encoder = JSONEncoder()
  let data = try encoder.encode(filter)
  let json = try JSONSerialization.jsonObject(with: data) as? [String: Any]
  
  // Verify each list item has both "value" and "type" fields
  let listValue = json?["fieldValue"]?["value"] as? [[String: Any]]
  #expect(listValue?.allSatisfy { $0["type"] != nil } == true)
}

2. No Mixed-Type List Validation

CloudKit lists can contain mixed types. The current tests only validate homogeneous lists (all strings or all ints). Consider adding test coverage for mixed-type lists if CloudKit supports them:

let mixedValues: [FieldValue] = [.string("value"), .int64(42)]
let filter = FilterBuilder.in("field", mixedValues)

3. Edge Case: Empty List

No test validates behavior with an empty list:

let filter = FilterBuilder.in("field", [])

This could fail at the CloudKit API level or cause unexpected behavior.

Performance Considerations ✅

The change from .map { Components.Schemas.FieldValue(from: $0).value } to .map { CustomFieldValue.CustomFieldValuePayload($0) } should have minimal performance impact:

• Both create intermediate objects during mapping
• The new approach actually does less work (one conversion vs. two-step conversion + extraction)
• For typical use cases (<200 items per IN filter as shown in tests), performance is negligible

Security Concerns ✅

No security issues identified. The change:

• Does not introduce injection vulnerabilities
• Does not expose sensitive data
• Maintains proper type safety through Swift's type system
• Follows CloudKit's API contract more correctly

Best Practices ✅

Following MistKit Guidelines:

• ✅ Uses internal visibility appropriately
• ✅ Maintains async/await patterns (no changes to async code)
• ✅ Follows existing code style and conventions
• ✅ Updates tests to match implementation changes
• ✅ Removes workaround comments and code properly

Swift Best Practices:

• ✅ Type-safe conversions
• ✅ No force unwrapping
• ✅ Proper use of map for transformations
• ✅ Clear, descriptive variable names in updated comments

Additional Observations

1. ArticleCloudKitService Optimization

The removal of in-memory filtering (lines 138-142 deleted) is a genuine optimization:

• Before: Query by GUID only, filter by feed in-memory (network: N items, filtered to M items)
• After: Query by GUID + feed together (network: M items directly)

This reduces network payload and memory usage when feedRecordName is specified.

2. Re-enabled Functionality

The ArticleSyncService.swift changes re-enable GUID-based deduplication that was previously disabled due to this bug. This is critical functionality for preventing duplicate articles.

3. Test Accuracy

The test update in ArticleCloudKitService+Query.swift (lines 117-123) correctly removes the mock for the non-matching article, reflecting that CloudKit now filters server-side. This makes the test more realistic.

Recommendations

1. Add serialization tests to verify type metadata preservation in JSON output
2. Add edge case tests for empty lists and mixed-type lists (if supported)
3. Consider adding a regression test that specifically validates the fix for issue CloudKit Web Services QueryFilter.in() returns HTTP 400 'Unexpected input' #192
4. Document the CloudKit API requirements around type metadata in code comments
5. Run integration tests against actual CloudKit Web Services (if not already done) to verify the fix works in production

Final Verdict: ✅ APPROVE with Suggestions

This is a well-implemented fix that:

• ✅ Correctly addresses the root cause
• ✅ Follows project conventions
• ✅ Includes appropriate test updates
• ✅ Enables previously broken functionality
• ✅ Optimizes query performance

The suggestions above are minor enhancements for test coverage and would not block merging.

All 311 MistKit tests and 115 CelestraCloud tests passing is excellent validation.

---

Review performed by Claude Code following MistKit's CLAUDE.md guidelines

[claude]

Pull Request Review: Fix QueryFilter IN/NOT_IN Serialization

Summary

This PR fixes a critical bug where IN and NOT_IN filters were stripping type metadata from list items, causing CloudKit Web Services to reject queries with HTTP 400 errors. The fix is minimal, focused, and correct.

---

Code Quality & Best Practices ✅

FilterBuilder.swift Changes (Lines 188, 204)
The core fix replaces:

Components.Schemas.FieldValue(from: $0).value

with:

CustomFieldValue.CustomFieldValuePayload($0)

Why this works:

• Components.Schemas.FieldValue(from:) creates a FieldValue with proper type metadata, but .value extracts only the raw payload, losing the type information
• CustomFieldValuePayload directly creates the payload while preserving type information through its enum cases
• CloudKit Web Services requires type metadata in list items for proper deserialization

Code Quality:

• ✅ Follows existing patterns (see line 108 in Components+FieldValue.swift which uses the same approach for list initialization)
• ✅ Minimal change - only touches the specific broken code
• ✅ No unnecessary refactoring or scope creep
• ✅ Properly uses internal visibility

---

Test Coverage ✅

ArticleCloudKitService+Query.swift:

• Updated test expectations to reflect server-side filtering behavior
• Changed from expecting 2 filters (1 query filter + 1 in-memory) to expecting 2 query filters combined
• Mock now correctly simulates CloudKit filtering behavior by returning only matching records
• Test validates the actual behavior users will see

Test Results:

• MistKit: 311/311 tests passing
• CelestraCloud: 115/115 tests passing
• Strong evidence the fix works correctly

---

Implementation Quality ✅

ArticleCloudKitService.swift:

• Removed unnecessary in-memory filtering workaround (lines 138-141 deleted)
• Now properly combines filters at query time (lines 116-119)
• Updated comments to reflect fixed behavior
• More efficient - filtering happens server-side rather than fetching extra records

ArticleSyncService.swift:

• Re-enabled GUID queries that were temporarily disabled
• Removed TODO/TEMPORARY comments
• Restores intended functionality

---

Performance Considerations ✅

Before:

• Fetched ALL articles matching GUIDs regardless of feed
• Filtered in-memory after transfer
• Wasted bandwidth and processing

After:

• CloudKit filters server-side using combined query
• Only matching records transferred
• Significant performance improvement for large datasets

---

Security Concerns ✅

No security issues identified:

• No user input validation changes
• No authentication/authorization changes
• No data exposure risks
• Type preservation actually improves data integrity

---

Potential Issues & Recommendations

Minor Concerns:

1. Type Safety Verification (Low Priority)

   • Consider adding a unit test that explicitly validates type metadata is preserved in list items
   • Example: Test that IN filter with mixed types (if supported) maintains individual type information

2. Documentation (Low Priority)

   • The PR description is excellent, but consider adding a code comment in FilterBuilder explaining why CustomFieldValuePayload is used instead of .value
   • This prevents future regressions if someone tries to "simplify" it

Suggested Addition:

// IN/NOT_IN filters must preserve type metadata for CloudKit Web Services.
// Use CustomFieldValuePayload directly rather than extracting .value from
// Components.Schemas.FieldValue to maintain type information in list items.
internal static func `in`(_ field: String, _ values: [FieldValue]) -> Components.Schemas.Filter {
  // ...
}

---

Verdict: ✅ APPROVE

This is an exemplary bug fix:

• Correctly identifies and fixes the root cause
• Minimal code changes with maximum impact
• Properly tested with comprehensive validation
• Follows existing codebase patterns
• Improves performance as a side effect
• Excellent PR description documenting the problem and solution

Recommendation: Merge after addressing the optional documentation suggestion above (not blocking).

---

Additional Notes

The fix demonstrates good understanding of CloudKit Web Services requirements and the MistKit type system. The decision to use CustomFieldValuePayload directly is architecturally sound given that:

1. It's used elsewhere for list handling (Components+FieldValue.swift:108)
2. It maintains the type/value pairing that CloudKit expects
3. It's the internal representation that eventually gets serialized

Great work! 🎉

[claude]

Code Review: Fix QueryFilter IN/NOT_IN serialization

Summary

This PR successfully fixes a critical bug where IN and NOT_IN filters were stripping type metadata from list items, causing CloudKit Web Services to reject queries with HTTP 400 errors. The fix is clean, well-tested, and enables important functionality that was previously disabled.

---

✅ Positive Aspects

1. Root Cause Fix is Correct

The core issue in FilterBuilder.swift:188,204 is properly addressed:

Before:

.listValue(values.map { Components.Schemas.FieldValue(from: $0).value })

After:

.listValue(values.map { CustomFieldValue.CustomFieldValuePayload($0) })

The problem was that .value was extracting only the raw payload (e.g., just the string "guid-1") while discarding the type metadata (type: .string). CloudKit requires both the value AND type for proper deserialization. Using CustomFieldValuePayload directly preserves the complete type information.

2. Excellent Impact

• Re-enables GUID queries in ArticleSyncService (lines 75-79)
• Removes inefficient in-memory filtering workaround
• Combines filters at query time for better performance
• All 311 MistKit tests + 115 CelestraCloud tests passing

3. Clean Code Changes

• Minimal diff (23 additions, 36 deletions) demonstrates surgical precision
• Removes extensive workaround comments explaining the limitation
• Updated comments accurately reflect new capability
• No over-engineering or scope creep

4. Proper Test Updates

The test changes in ArticleCloudKitService+Query.swift correctly reflect the new behavior:

• Mock now returns only server-filtered results (line 122)
• Expectations updated to verify 2 filters instead of 1 (line 127)
• Comments explain the server-side filtering behavior

---

🔍 Observations & Minor Concerns

1. Test Coverage Gap

The current test at line 113 (testQueryArticlesByGUIDsFiltersByFeed) doesn't fully validate the fix:

mock.queryRecordsResult = .success([
  createMockRecordInfo(recordName: "article-1", fields: matchingFields)
])

The mock returns only the matching article, simulating server-side filtering. However, this doesn't verify that:

1. The IN filter was properly serialized with type metadata
2. CloudKit would actually accept the query without 400 errors

Recommendation: Consider adding an integration test (or at least a comment) that validates the actual serialized JSON includes type information like:

{
  "fieldName": "guid",
  "comparator": "IN",
  "fieldValue": {
    "type": "LIST",
    "value": [{"type": "STRING", "value": "guid-1"}, ...]
  }
}

2. Old Code Still Present

While the PR updates FilterBuilder.swift, the old problematic code still exists in ArticleCloudKitService.swift:113-122:

// CloudKit Web Services has issues with combining .in() with other filters.
// Current approach: Use .in() ONLY for GUID filtering (single filter, no combinations).
// Feed filtering is done in-memory (line 135-136) to avoid the .in() + filter issue.

This comment is outdated and contradicts the fix. It should be removed since the issue is now resolved.

3. Test Assertion Comment Mismatch

In the updated test file (line 127), the comment says:

// Should have 2 filters: IN for GUID + EQUALS for feedRecordName
#expect(mock.queryCalls[0].filters?.count == 2)

But looking at the current ArticleCloudKitService.swift:113-122, the code still only uses ONE filter. This suggests either:

• The file in the working directory is stale, OR
• The test expectations are incorrect

This is concerning - the test expects 2 filters but the implementation only sends 1.

---

🐛 Critical Issue Found

After reviewing the diff more carefully, I notice the ArticleCloudKitService.swift changes show:

Lines 113-122 in the PR:

// Query articles by GUID using the IN filter.
// Now that issue #192 is fixed, we can combine .in() with other filters.
// If feedRecordName is specified, we filter at query time for efficiency.
var filters: [QueryFilter] = [.in("guid", guids.map { FieldValue.string($0) })]
if let feedName = feedRecordName {
  filters.append(.equals("feedRecordName", FieldValue.string(feedName)))
}

This is correct and matches the test expectations! The old code I saw was from reading the file at HEAD, not from the PR diff.

---

🎯 Final Assessment

Code Quality: ⭐⭐⭐⭐½ (4.5/5)

• Clean implementation
• Proper fix for root cause
• Good documentation updates

Bug Risk: ⭐⭐⭐⭐⭐ (5/5)

• Very low risk - the fix is simple and correct
• Extensive test coverage (426 tests passing)
• Re-enables previously working functionality

Performance: ⭐⭐⭐⭐⭐ (5/5)

• Eliminates in-memory filtering overhead
• Server-side filtering is significantly more efficient
• Proper use of CloudKit query optimization

Security: ✅ No concerns

• No security implications
• Standard CloudKit query operations

---

📋 Recommendations

Must Fix Before Merge:

None - the code is ready to merge.

Nice to Have:

1. Add serialization test - Verify the IN/NOT_IN filters serialize with proper type metadata
2. Integration test - Add a test that actually hits CloudKit (or mock at HTTP level) to validate no 400 errors
3. Documentation - Consider adding a code comment in FilterBuilder.swift explaining why CustomFieldValuePayload is used instead of extracting .value

Example comment suggestion for FilterBuilder.swift:

// IMPORTANT: Use CustomFieldValuePayload directly to preserve type metadata.
// CloudKit requires both the value AND type information for each list item.
// Extracting .value would strip the type, causing 400 errors from the API.
.listValue(values.map { CustomFieldValue.CustomFieldValuePayload($0) })

---

✅ Approval

LGTM - This PR successfully fixes a critical bug and is well-tested. The changes are minimal, focused, and correct. Great work diagnosing and fixing this issue!

The only minor improvement would be additional test coverage for the serialization format, but the existing tests are sufficient to verify functionality.

Co-Authored-By: Claude Sonnet 4.5 noreply@anthropic.com