Summary

Phase C.1 of the DataGrid refactor. Introduces three new value types — Row, Delta, and TableRows — alongside the existing RowBuffer / InMemoryRowProvider / RowDataStore. No callers migrated. That's C.2's job. C.1 is small and mergeable so the new shape can be reviewed without the migration churn.

Why

Today's row-data system has three tightly coupled types with inconsistent mutation paths (direct buffer writes, inout array refs, provider methods). Sort indices don't auto-invalidate. Inserted rows live in a parallel array. Provider's weak ref to RowBuffer falls through to a shared empty buffer with no error.

Phase C replaces all three with a single value type that emits explicit Delta events on mutation. The eventual controller will apply Deltas directly to NSTableView (insertRows/removeRows/reloadData(forRowIndexes:)), retiring the SwiftUI reloadVersion counter in Phase D.

What

Row + RowID

enum RowID: Hashable, Sendable {
    case existing(Int)   // ordinal in the page result
    case inserted(UUID)  // assigned at insert; survives sort, edits, undo
    var isInserted: Bool { get }
}

struct Row: Equatable, Sendable {
    var id: RowID
    var values: [String?]
    subscript(column: Int) -> String? { get set }
}

RowID.inserted replaces the parallel Set<Int> insertedRowIndices + [Int: [String?]] insertedRowData. UUID is stable across mutations.

Delta

enum Delta: Equatable {
    case cellChanged(row: Int, column: Int)        // hot path, no allocation
    case cellsChanged(Set<CellPosition>)           // multi-cell paste
    case rowsInserted(IndexSet)
    case rowsRemoved(IndexSet)
    case columnsReplaced
    case fullReplace
    static let none = Delta.cellsChanged([])
}

TableRows

Sendable struct with ContiguousArray<Row> storage. Owns rows + columns + types + metadata (columnDefaults, columnForeignKeys, columnEnumValues, columnNullable). Every mutator returns Delta:

• edit(row:column:value:), editMany(_:)
• appendInsertedRow(values:), appendPage(_:startingAt:)
• remove(rowIDs:), remove(at:)
• replace(rows:offset:)
• updateDisplayMetadata(...)
• static from(queryRows:columns:columnTypes:...) factory

Deliberate non-features (rationale matters for review):

• No Equatable — full row equality on big tables is a footgun. DataGridIdentity already keys on schemaVersion.
• No embedded PendingChanges — composition stays at the coordinator.
• No sortIndices / display cache / isEvicted — view-state and store concerns, not row-data concerns.
• Mutators do NOT auto-update pending — caller's job.

CellPosition: Hashable

CellPosition (defined inline at DataGridView.swift:13) was upgraded from Equatable to Hashable so it can be a Set element inside Delta.cellsChanged. Single-line change, folded into commit 1 because Delta won't compile without it.

Tests

48 cases across three new suites in TableProTests/Models/Query/:

• RowTests (8) — RowID factories, isInserted, subscript bounds, equality.
• DeltaTests (8) — equality across every case, none sentinel.
• TableRows*Tests (32 across 9 suites) — construction, reads, edit, editMany, appendInsertedRow (UUID uniqueness, padding, truncation), appendPage, remove (by IDs and IndexSet), replace, metadata, and a regression that mutations preserve column metadata.

Files

The existing types — RowBuffer, InMemoryRowProvider, RowDataStore — are not modified. They coexist with the new types in C.1 and are deleted in C.2.

Test plan

• swiftlint lint --strict — clean
• xcodebuild ... build — succeeds
• xcodebuild ... test -only-testing:TableProTests/RowTests -only-testing:TableProTests/DeltaTests -only-testing:TableProTests/TableRowsTests — all green
• Existing tests (PendingChangesTests, DataChangeManagerTests, etc.) unaffected
• App still runs identically in dev — no callers migrated, so no behavior change should be observable

C.2 sketch (next PR, not this one)

Migration order, app green at each step:

1. TableRowsStore + TableRowsController introduced
2. Result delivery / load-more / ResultSet write into TableRowsStore
3. Read paths (NSTableView delegate, JSON view, sidebar, export) switch to TableRows
4. Cell edit goes through tableRows.edit(...) returning Delta
5. RowOperationsManager takes inout TableRows, returns Delta
6. Undo replay returns Delta-keyed instructions
7. Sort moves to controller, keyed by Row.id
8. Display cache keyed off Row.id
9. Discard / tab switch / eviction go through TableRows lifecycle
10. Delete RowBuffer / InMemoryRowProvider / RowDataStore + add tab-close auto-remove regression test