docs: update documentation for extraction functions migration

- Add ExtractionFunctions.md reference document
- Update database-schema spec with 11 extraction functions
- Update data-access spec to document extraction function approach
- Update search-processing spec with new query builder interface
- Add Database.Tests to Testing.md architecture doc
- Update DataFlow.md with extraction function flow

openspec/specs/data-access/spec.md

@@ -467,40 +467,65 @@ catch (OracleException ex)
 
 ---
 
-### Requirement: Table-valued parameter support
+### Requirement: Search criteria extraction via SQL functions
 
-The system SHALL use DataTable for SQL Server table-valued parameters in lookup methods.
+The system SHALL use SQL extraction functions to retrieve filter criteria directly from the `Search.Criteria` JSON column.
 
 #### Implementation Pattern
 
+Search query building now uses SearchId to invoke extraction functions rather than passing filter values from C#:
+
 ```csharp
-public async Task<List<Item>> LookupItemsAsync(List<string> itemNumbers, CancellationToken ct = default)
+public SearchQueryResult BuildSearchQuery(int searchId)
 {
-    await using var connection = await _connectionFactory.CreateLotFinderConnectionAsync(ct);
+    // Query builder generates SQL that calls extraction functions
+    // Example generated SQL fragment:
+    // INSERT INTO #P_WorkOrders SELECT WorkOrderNumber FROM dbo.fn_GetSearchWorkOrders(@SearchId)
+    // INSERT INTO #P_ItemNumbers SELECT ItemNumber FROM dbo.fn_GetSearchItemNumbers(@SearchId)
 
-    var table = new DataTable();
-    table.Columns.Add("ItemNumber", typeof(string));
-    foreach (var itemNumber in itemNumbers)
-    {
-        table.Rows.Add(itemNumber);
-    }
-
-    var parameters = new DynamicParameters();
-    parameters.Add("@itemNumbers", table.AsTableValuedParameter("dbo.ItemNumberFilterParameter"));
-
-    return (await connection.QueryAsync<Item>(
-        LotFinderQueries.SQL_LOOKUP_ITEMS,
-        parameters,
-        commandTimeout: _options.Value.DefaultTimeoutSeconds))
-        .AsList();
+    return new SearchQueryResult(sql, new { SearchId = searchId });
 }
 ```
 
 #### Business Rules
 
-- TVPs SHALL use `AsTableValuedParameter` extension with correct type name
+- Query builder SHALL accept only `searchId` parameter (not full criteria object)
+- SQL queries SHALL call extraction functions to populate temporary filter tables
+- Extraction functions handle JSON parsing and validation in SQL Server
+- Invalid JSON or missing criteria results in empty filter sets (no errors thrown)
+
+#### Available Extraction Functions
+
+| Function | Returns |
+|----------|---------|
+| `fn_GetSearchMinimumDt` | DATETIME2 scalar |
+| `fn_GetSearchMaximumDt` | DATETIME2 scalar |
+| `fn_GetSearchExtractMisData` | BIT scalar |
+| `fn_GetSearchWorkOrders` | WorkOrderNumber table |
+| `fn_GetSearchItemNumbers` | ItemNumber table |
+| `fn_GetSearchProfitCenters` | Code table |
+| `fn_GetSearchWorkCenters` | Code table |
+| `fn_GetSearchOperatorIDs` | OperatorID table |
+| `fn_GetSearchComponentLots` | LotNumber, ItemNumber table |
+| `fn_GetSearchPartOperations` | ItemNumber, OperationNumber, MisNumber, MisRevision table |
+
+#### Scenario: Build search query with extraction functions
+
+- **WHEN** `BuildSearchQuery(123)` is called for a search with work order filter
+- **THEN** generated SQL includes `SELECT WorkOrderNumber FROM dbo.fn_GetSearchWorkOrders(123)`
+- **AND** only the `@SearchId` parameter is passed to the query
+
+---
+
+### Requirement: Table-valued parameter support for lookups
+
+The system SHALL use DataTable for SQL Server table-valued parameters in reference data lookup methods.
+
+#### Business Rules
+
+- TVPs are used for batch lookups (LookupItemsAsync, LookupWorkordersAsync, etc.)
+- TVPs are NOT used for search query execution (replaced by extraction functions)
 - DataTable column names SHALL match TVP type column names
-- TVPs enable efficient batch lookups with single database round-trip
 
 #### Scenario: Batch lookup with TVP