DynamicCustomTool: Align tool input schema with DB metadata at runtime

[souvikghosh04]

Why make this change?

• Closes DynamicCustomTool: Align tool input schema with DB metadata at runtime #3615

Custom MCP tools used a permissive multi-type array for all parameters in the input schema. MCP clients had no type information to guide users or validate inputs before execution.

What is this change?

• InitializeMetadata: Resolves StoredProcedureDefinition.Parameters from the metadata provider and builds a typed JSON Schema (integer/number/boolean/string) for each DB-discovered parameter.
• Fallback: Falls back to config-based permissive schema when DB metadata is unavailable.
• Both modes: Applied in HTTP mode (McpToolRegistryInitializer) and stdio mode (McpStdioHelper) via shared McpToolRegistry.InitializeAndRegisterTools helper.
• Default descriptions: Surfaces (default: value) in parameter descriptions when HasConfigDefault is set.

How was this tested?

• Unit Tests

Test	Scenario
UsesDbMetadata_WhenInitialized	Schema uses typed params after InitializeMetadata
FallsBackToConfig_WhenDbMetadataUnavailable	Permissive array when no metadata factory
UsesConfigSchema_WhenNotInitialized	Config schema used without InitializeMetadata call
IncludesAllDbDiscoveredParams	Params not in config but in DB appear in schema
MapsSystemTypesToJsonSchemaTypes (x12)	int/long/short/byte to integer, float/double/decimal to number, bool to boolean, string/Guid/DateTime to string
UsesPermissiveType_WhenSystemTypeIsNull	Null SystemType falls back to multi-type array
IncludesDefaultInDescription	(default: value) in description
ZeroParamSP_ReturnsEmptyProperties	Empty properties for zero-param SP

• Integration Tests

Test	Scenario
InitializeMetadata_SchemaReflectsDbParameterTypes (x3)	int->integer, varchar->string mapping against live DB
InitializeMetadata_ZeroParamSP_HasEmptyProperties	Zero-param SP has empty properties from DB metadata
InitializeMetadata_DescriptionIncludesConfigDefaults (x2)	Config defaults (randomX, 1234) in descriptions

• Manual Testing

Tool	Before	After
get_book(id)	type: [...]	type: integer
insert_book(title, publisher_id)	permissive	string, integer + defaults in desc
update_book_title(id, title)	permissive	integer, string + defaults in desc
get_books (zero-param)	empty	empty
End-to-end execution get_book(id=1)	N/A	returns book record

Sample Request(s)

tools/list response (get_book schema after fix):

{ "name": "get_book", "inputSchema": { "type": "object", "properties": { "id": { "type": "integer", "description": "Parameter id" } } } }

[Copilot]

Pull request overview

This PR updates MCP DynamicCustomTool registration so the tool input JSON Schema reflects stored procedure parameter metadata discovered from the database at runtime (with a config-based permissive fallback), improving client-side validation and parameter discoverability.

Changes:

• Added post-DI initialization (InitializeMetadata) to build/cache a DB-metadata-based input schema for DynamicCustomTool.
• Initialized metadata before tool registration in both HTTP-hosted (McpToolRegistryInitializer) and stdio (McpStdioHelper) MCP modes.
• Added unit tests covering schema alignment behaviors (typed mapping, fallback behavior, defaults in descriptions, zero-parameter SP).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/Azure.DataApiBuilder.Mcp/Core/DynamicCustomTool.cs	Adds DB-metadata-based schema building and caching, plus type mapping and default-in-description support.
src/Azure.DataApiBuilder.Mcp/Core/McpToolRegistryInitializer.cs	Ensures custom tools initialize DB-backed schema before being registered (HTTP mode).
src/Service/Utilities/McpStdioHelper.cs	Ensures custom tools initialize DB-backed schema before being registered (stdio mode).
src/Service.Tests/Mcp/DynamicCustomToolTests.cs	Adds unit tests validating DB-metadata schema enrichment and fallback behaviors.

[aaronburtle]

Looks good, thanks for fixing everything!