feat(mssql-json): enable JSON data type - type mapping, error codes and fixtures (Phase 2)

Treat SQL Server 2025+ JSON columns exactly like string columns (2026-06-09 design). Two-line production delta plus test fixture and unit tests (T002-T007).

- TypeHelper._sqlDbTypeToType[SqlDbType.Json] = typeof(string) (T004)

- MsSqlDbExceptionParser BadRequestExceptionCodes += 13608-13614 so SQL JSON errors map to HTTP 400 (T006)

- SqlTypeConstants: json -> supported (T004)

- profiles table + 5 seed rows + Profile entity fixture (T002/T003)

- unit tests for json type mapping and 400 error mapping (T005/T007)

No changes to PostgreSQL/MySQL/DwSql/CosmosDB (FR-012).

Author: souvikghosh04

specs/001-mssql-json-type/tasks.md

@@ -52,6 +52,90 @@ both prerequisites and fails fast if either is missing.
 
 ---
 
+## PR Delivery Plan (phased)
+
+This feature ships as **4 phased PRs**. "Phase" here is the *delivery /
+PR* phase (coarse-grained) and is distinct from the fine-grained
+`## Phase 1..7` execution sections further down this file. The
+mapping column ties each PR back to those execution sections and task
+IDs.
+
+The **production delta is only two functional lines** (T004 + T006);
+every other task is a test fixture or an integration test. The split
+below is therefore driven by review load, not by risk to `main`.
+
+### Phase 1 — .NET 10 + SqlClient 6.x upgrade  ✅ MERGED (PR #3656)
+
+**Title**: `[Phase 1] Upgrade to .NET 10 and Microsoft.Data.SqlClient 6.x`
+
+**Description**:
+> Joint prerequisite for MSSQL JSON support. Bumps the target framework
+> `net8.0 → net10.0` across every `src/**/*.csproj`, pins the SDK in
+> `global.json` (`10.0.x`), updates `dotnet-version` in CI workflows,
+> and upgrades `Microsoft.Data.SqlClient 5.2.3 → 6.x`. Required because
+> `SqlDbType.Json` is a BCL enum value (added in .NET 9) that does not
+> resolve on .NET 8 regardless of SqlClient version. Also refreshes the
+> SqlClient SNI license under `external_licenses/` and regenerates the
+> NOTICE file. No functional DAB behavior change.
+
+**Covers**: upstream dependency (this file's "Upstream Dependency" section) · **Status**: merged, `main` now ships `net10.0` + SqlClient 6.1.5.
+
+### Phase 2 — JSON engine enablement  ← current PR
+
+**Title**: `[Phase 2] Enable MSSQL JSON data type — type mapping, error codes & fixtures`
+
+**Description**:
+> Delivers the entire functional behavior for SQL Server 2025+ `JSON`
+> columns by treating them exactly like `string` columns (2026-06-09
+> design). Two-line production delta:
+> - `TypeHelper._sqlDbTypeToType[SqlDbType.Json] = typeof(string)` so
+>   `JSON` columns flow through every existing string read/write path.
+> - `MsSqlDbExceptionParser.BadRequestExceptionCodes += 13608–13614`
+>   so SQL Server JSON-validation errors surface as HTTP `400` (not `500`).
+>
+> Adds the `Profile` / `profiles` test fixture (table + 5 seed rows +
+> DAB entity) and two unit tests. The 13608–13614 range is the starting
+> set and is pruned to the actually-triggered numbers in Phase 4.
+> No changes to PostgreSQL / MySQL / DwSql / CosmosDB (FR-012).
+
+**Covers**: execution Phases 2–4 · **Tasks**: T002–T007 · **FRs**: FR-001, FR-004, FR-007, FR-012, FR-014.
+
+### Phase 3 — CRUD integration tests
+
+**Title**: `[Phase 3] MSSQL JSON — CRUD integration tests (REST / GraphQL / MCP)`
+
+**Description**:
+> Test-only PR (no production code). Pins the happy-path behavior of
+> JSON columns across all surfaces under `TestCategory=MsSql`:
+> schema-discovery (OpenAPI `type: string`, GraphQL `String` scalar,
+> MCP describe_entities parity — US1), read single & collection
+> (US2/US3), insert (US4), update via PUT/PATCH/GraphQL (US5) and
+> delete (US6). Confirms Phase 2's engine change is correct end-to-end.
+
+**Covers**: execution Phase 5, stories US1–US6 · **Tasks**: T008–T019 · **FRs**: FR-001, FR-002, FR-003, FR-004, FR-005, FR-006, FR-008, FR-011, FR-013, FR-017.
+
+### Phase 4 — Errors, filters, edge cases, regression & polish
+
+**Title**: `[Phase 4] MSSQL JSON — error handling, filter/orderby pass-through, edge cases & regression`
+
+**Description**:
+> Test-only PR that completes coverage and hardens the feature.
+> - SQL Server JSON errors → HTTP `400` / GraphQL `BAD_REQUEST` with the
+>   SQL error number in the body (US7); uses these tests to **prune** the
+>   speculative 13608–13614 error-code set added in Phase 2 to the
+>   numbers SQL Server actually raises.
+> - `$filter` / `$orderby` pass-through in both success and SQL-rejected
+>   directions (US9) — no DAB operator allow-list; everything forwards to
+>   SQL Server.
+> - Null handling (US8) and edge cases: unicode round-trip, nested object,
+>   array payload.
+> - Non-MSSQL regression guard (diff + baseline test counts for
+>   PostgreSQL / MySQL / CosmosDB), `dotnet format`, and quickstart smoke.
+
+**Covers**: execution Phase 5 (US7–US9 + edge cases) and Phases 6–7 · **Tasks**: T020–T034 · **FRs**: FR-007, FR-008, FR-009, FR-010, FR-016, SC-001, SC-002, SC-004.
+
+---
+
 ## Phase 1: Pre-flight (Blocking)
 
 **Purpose**: Confirm the upstream prerequisite PR has landed before
@@ -73,8 +157,8 @@ files.
 **Purpose**: Create the `Profile` / `profiles` test fixture so
 integration tests have a database table and DAB entity to bind to.
 
-- [ ] T002 Add the `profiles` table and the 5 seed rows defined in [data-model.md](./data-model.md) §Table Definition to [src/Service.Tests/DatabaseSchema-MsSql.sql](../../src/Service.Tests/DatabaseSchema-MsSql.sql). Format per copilot-instructions.md MSSQL rules (poorsql, 4-space indent, trailing commas). **MUST NOT touch** `DatabaseSchema-PostgreSql.sql`, `DatabaseSchema-MySql.sql`, `DatabaseSchema-DwSql.sql`, or any CosmosDB schema file (FR-012, Principle I).
-- [ ] T003 Add the `Profile` entity entry to [src/Service.Tests/dab-config.MsSql.json](../../src/Service.Tests/dab-config.MsSql.json) (source object `dbo.profiles`, anonymous read role for tests as per existing fixture patterns), per [data-model.md](./data-model.md) §DAB Entity. Run `dab validate` against the updated config (no [schemas/dab.draft.schema.json](../../schemas/dab.draft.schema.json) change expected per FR-014 / R11).
+- [x] T002 Add the `profiles` table and the 5 seed rows defined in [data-model.md](./data-model.md) §Table Definition to [src/Service.Tests/DatabaseSchema-MsSql.sql](../../src/Service.Tests/DatabaseSchema-MsSql.sql). Format per copilot-instructions.md MSSQL rules (poorsql, 4-space indent, trailing commas). **MUST NOT touch** `DatabaseSchema-PostgreSql.sql`, `DatabaseSchema-MySql.sql`, `DatabaseSchema-DwSql.sql`, or any CosmosDB schema file (FR-012, Principle I).
+- [x] T003 Add the `Profile` entity entry to [src/Service.Tests/dab-config.MsSql.json](../../src/Service.Tests/dab-config.MsSql.json) (source object `dbo.profiles`, anonymous read role for tests as per existing fixture patterns), per [data-model.md](./data-model.md) §DAB Entity. Run `dab validate` against the updated config (no [schemas/dab.draft.schema.json](../../schemas/dab.draft.schema.json) change expected per FR-014 / R11).
 
 **Checkpoint**: Test fixture exists; integration tests added in Phase 5 will resolve their entity references. No production behavior change yet.
 
@@ -86,8 +170,8 @@ integration tests have a database table and DAB entity to bind to.
 (R1, R2). Single-line dictionary edit; once landed, JSON columns flow
 through every read / write path that already supports `string`.
 
-- [ ] T004 Add `[SqlDbType.Json] = typeof(string)` to `TypeHelper._sqlDbTypeToType` in [src/Core/Services/TypeHelper.cs](../../src/Core/Services/TypeHelper.cs) (R1). Position the entry adjacent to the existing `NVarChar` / `Text` entries to keep the dictionary readable.
-- [ ] T005 [P] Unit test: extend the `TypeHelper` test suite (under [src/Service.Tests](../../src/Service.Tests)) to assert `GetSystemTypeFromSqlDbType("json")` returns `typeof(string)` and that `GetJsonDataTypeFromSystemType(typeof(string))` continues to return `JsonDataType.String` (regression check for R2).
+- [x] T004 Add `[SqlDbType.Json] = typeof(string)` to `TypeHelper._sqlDbTypeToType` in [src/Core/Services/TypeHelper.cs](../../src/Core/Services/TypeHelper.cs) (R1). Position the entry adjacent to the existing `NVarChar` / `Text` entries to keep the dictionary readable.
+- [x] T005 [P] Unit test: extend the `TypeHelper` test suite (under [src/Service.Tests](../../src/Service.Tests)) to assert `GetSystemTypeFromSqlDbType("json")` returns `typeof(string)` and that `GetJsonDataTypeFromSystemType(typeof(string))` continues to return `JsonDataType.String` (regression check for R2).
 
 **Checkpoint**: Once T004 is merged, `MsSqlMetadataProvider.SqlToCLRType` resolves JSON columns; `OpenApiDocumentor` and `SchemaConverter` emit `string` / `String` automatically. Phase 5 US1 integration tests transition from red to green.
 
@@ -101,8 +185,8 @@ SQL errors surface as `400` instead of `500`. Covers BOTH malformed
 JSON on write AND filter operators SQL Server cannot evaluate
 against a JSON column (FR-007; R4 as elevated 2026-06-09).
 
-- [ ] T006 Extend `MsSqlDbExceptionParser.BadRequestExceptionCodes` in [src/Core/Resolvers/MsSqlDbExceptionParser.cs](../../src/Core/Resolvers/MsSqlDbExceptionParser.cs) to include the SQL Server JSON-validation error numbers (R4 lists 13608–13614 as the starting set). PRUNE the speculative set to the actually-triggered numbers using T013 / T014 / T017 / T018 during implementation. Verify that the response body includes the SQL Server error number (R4 notes the existing error envelope serializer may need a small adjustment — verify and amend in this same task or call out a follow-up).
-- [ ] T007 [P] Unit test: add a `MsSqlDbExceptionParserTests` case (under [src/Service.Tests](../../src/Service.Tests)) asserting that a `SqlException` carrying each of the appended error numbers maps to `HttpStatusCode.BadRequest` via `GetHttpStatusCodeForException`, while a still-unknown number maps to its prior status (regression). Uses the existing `MakeSqlException`-style helper if present, else mocks `SqlException` via reflection per existing test patterns.
+- [x] T006 Extend `MsSqlDbExceptionParser.BadRequestExceptionCodes` in [src/Core/Resolvers/MsSqlDbExceptionParser.cs](../../src/Core/Resolvers/MsSqlDbExceptionParser.cs) to include the SQL Server JSON-validation error numbers (R4 lists 13608–13614 as the starting set). PRUNE the speculative set to the actually-triggered numbers using T013 / T014 / T017 / T018 during implementation. Verify that the response body includes the SQL Server error number (R4 notes the existing error envelope serializer may need a small adjustment — verify and amend in this same task or call out a follow-up).
+- [x] T007 [P] Unit test: add a `MsSqlDbExceptionParserTests` case (under [src/Service.Tests](../../src/Service.Tests)) asserting that a `SqlException` carrying each of the appended error numbers maps to `HttpStatusCode.BadRequest` via `GetHttpStatusCodeForException`, while a still-unknown number maps to its prior status (regression). Uses the existing `MakeSqlException`-style helper if present, else mocks `SqlException` via reflection per existing test patterns.
 
 **Checkpoint**: Once T006 lands, every SQL Server JSON error surfaces as 400 / `BAD_REQUEST` with the SQL error number in the response body. T013 / T014 (malformed write) and T017 / T018 (unsupported filter operator) go green.
 

src/Core/Models/SqlTypeConstants.cs

@@ -47,6 +47,7 @@ public static class SqlTypeConstants
         { "time", true },                 // SqlDbType.Time
         { "datetime2", true },            // SqlDbType.DateTime2
         { "datetimeoffset", true },       // SqlDbType.DateTimeOffset
+        { "json", true },                 // SqlDbType.Json (SQL Server 2025+) treated as string
         { "", false },                    // SqlDbType.Udt and SqlDbType.Structured provided by SQL as empty strings (unsupported)
         { "numeric", true}                // Not present in SqlDbType, however can be returned by sql functions like LAG and should map to decimal.
     };

src/Core/Resolvers/MsSqlDbExceptionParser.cs

@@ -30,7 +30,10 @@ public MsSqlDbExceptionParser(RuntimeConfigProvider configProvider) : base(confi
                 "4435", "4436", "4437", "4438", "4439", "4440", "4441",
                 "4442", "4443", "4444", "4445", "4446", "4447", "4448",
                 "4450", "4451", "4452", "4453", "4454", "4455", "4456",
-                "4457", "4933", "4934", "4936", "4988", "8102"
+                "4457", "4933", "4934", "4936", "4988", "8102",
+                // JSON data type validation errors (SQL Server 2025+). Invalid JSON
+                // supplied for a json column is a client error, mapped to HTTP 400.
+                "13608", "13609", "13610", "13611", "13612", "13613", "13614"
             });
 
             TransientExceptionCodes.UnionWith(new List<string>

src/Core/Services/TypeHelper.cs

@@ -97,6 +97,7 @@ public static class TypeHelper
             [SqlDbType.Float] = typeof(double),
             [SqlDbType.Image] = typeof(byte[]),
             [SqlDbType.Int] = typeof(int),
+            [SqlDbType.Json] = typeof(string),
             [SqlDbType.Money] = typeof(decimal),
             [SqlDbType.NChar] = typeof(char),
             [SqlDbType.NText] = typeof(string),

src/Service.Tests/DatabaseSchema-MsSql.sql

@@ -57,6 +57,7 @@ DROP TABLE IF EXISTS mappedbookmarks;
 DROP TABLE IF EXISTS fte_data;
 DROP TABLE IF EXISTS intern_data;
 DROP TABLE IF EXISTS books_sold;
+DROP TABLE IF EXISTS profiles;
 DROP TABLE IF EXISTS default_with_function_table;
 DROP TABLE IF EXISTS [DimAccount]
 DROP TABLE IF EXISTS date_only_table;
@@ -826,3 +827,17 @@ INSERT INTO date_only_table( event_date, event_time, event_timestamp)
 VALUES ('2023-01-01', '08:30:00', '2023-01-01 08:30:00'), 
        ('2023-02-15', '12:45:00', '2023-02-15 12:45:00'), 
        ('2023-03-30', '17:15:00', '2023-03-30 17:15:00');
+
+CREATE TABLE profiles (
+    id int IDENTITY(1, 1) PRIMARY KEY,
+    metadata json NULL
+);
+
+SET IDENTITY_INSERT profiles ON
+INSERT INTO profiles (id, metadata)
+VALUES (1, N'{"role":"admin","tier":3}'),
+       (2, N'{"tags":["a","b","c"]}'),
+       (3, N'{"nested":{"key":{"deep":true}}}'),
+       (4, N'{"unicode":"éü😀"}'),
+       (5, NULL);
+SET IDENTITY_INSERT profiles OFF

src/Service.Tests/OpenApiDocumentor/CLRtoJsonValueTypeUnitTests.cs

@@ -111,4 +111,17 @@ public void ResolveUnderlyingTypeForNullableValueType(Type nullableType)
         Assert.AreNotEqual(notExpected: JsonDataType.Undefined, actual: TypeHelper.GetJsonDataTypeFromSystemType(nullableType));
         Assert.IsNotNull(TypeHelper.GetDbTypeFromSystemType(nullableType));
     }
+
+    /// <summary>
+    /// Validates that the SQL Server 2025+ 'json' data type literal resolves to the
+    /// CLR string type and maps to JsonDataType.String, i.e. DAB treats a JSON column
+    /// just like a string column.
+    /// </summary>
+    [TestMethod]
+    public void JsonSqlDbTypeResolvesToString()
+    {
+        Type resolvedType = TypeHelper.GetSystemTypeFromSqlDbType("json");
+        Assert.AreEqual(typeof(string), resolvedType);
+        Assert.AreEqual(JsonDataType.String, TypeHelper.GetJsonDataTypeFromSystemType(resolvedType));
+    }
 }

src/Service.Tests/UnitTests/DbExceptionParserUnitTests.cs

@@ -94,5 +94,42 @@ public void TestIsTransientExceptionMethod(bool expected, int number)
 
             Assert.AreEqual(expected, dbExceptionParser.IsTransientException(SqlTestHelper.CreateSqlException(number)));
         }
+
+        /// <summary>
+        /// Validates that JSON data type validation error codes raised by SQL Server 2025+
+        /// when invalid JSON is supplied for a json column are mapped to HTTP 400 Bad Request.
+        /// </summary>
+        /// <param name="number">SQL error code populated in SqlException.Number.</param>
+        [DataTestMethod]
+        [DataRow(13608, DisplayName = "JSON validation error code 13608 maps to 400")]
+        [DataRow(13609, DisplayName = "JSON validation error code 13609 maps to 400")]
+        [DataRow(13610, DisplayName = "JSON validation error code 13610 maps to 400")]
+        [DataRow(13611, DisplayName = "JSON validation error code 13611 maps to 400")]
+        [DataRow(13612, DisplayName = "JSON validation error code 13612 maps to 400")]
+        [DataRow(13613, DisplayName = "JSON validation error code 13613 maps to 400")]
+        [DataRow(13614, DisplayName = "JSON validation error code 13614 maps to 400")]
+        public void TestJsonValidationErrorsMapToBadRequest(int number)
+        {
+            RuntimeConfig mockConfig = new(
+                Schema: "",
+                DataSource: new(DatabaseType.MSSQL, "", new()),
+                Runtime: new(
+                    Rest: new(),
+                    GraphQL: new(),
+                    Mcp: new(),
+                    Host: new(null, null, HostMode.Development)
+                ),
+                Entities: new(new Dictionary<string, Entity>())
+            );
+            MockFileSystem fileSystem = new();
+            fileSystem.AddFile(FileSystemRuntimeConfigLoader.DEFAULT_CONFIG_FILE_NAME, new MockFileData(mockConfig.ToJson()));
+            FileSystemRuntimeConfigLoader loader = new(fileSystem);
+            RuntimeConfigProvider provider = new(loader);
+            DbExceptionParser dbExceptionParser = new MsSqlDbExceptionParser(provider);
+
+            Assert.AreEqual(
+                System.Net.HttpStatusCode.BadRequest,
+                dbExceptionParser.GetHttpStatusCodeForException(SqlTestHelper.CreateSqlException(number)));
+        }
     }
 }

src/Service.Tests/dab-config.MsSql.json

@@ -3991,6 +3991,43 @@
         }
       ]
     },
+    "Profile": {
+      "source": {
+        "object": "profiles",
+        "type": "table",
+        "key-fields": [
+          "id"
+        ]
+      },
+      "graphql": {
+        "enabled": true,
+        "type": {
+          "singular": "Profile",
+          "plural": "Profiles"
+        }
+      },
+      "rest": {
+        "enabled": true
+      },
+      "permissions": [
+        {
+          "role": "anonymous",
+          "actions": [
+            {
+              "action": "*"
+            }
+          ]
+        },
+        {
+          "role": "authenticated",
+          "actions": [
+            {
+              "action": "*"
+            }
+          ]
+        }
+      ]
+    },
     "GetBooksAuth": {
       "source": {
         "object": "get_books",