[Bug]: Preserve autoentity-generated entities in multi-source MCP runtime configuration #3729

What happened?

When multiple child configurations use SQL autoentities with MCP enabled, DAB discovers entities during child/provider initialization but describe_entities returns NoEntitiesConfigured from the final merged runtime configuration. A parent with one child and each child tested independently work, while a parent with two or more children reproduces the failure.

Expected behavior: all generated entities from every child configuration should be present in the shared runtime configuration and returned by describe_entities, with each entity mapped to its originating data source.

Observed behavior: startup completes successfully and dab validate reports discovered entities, but MCP sees no usable entities. The issue appears to occur while propagating generated autoentities from per-child/per-datasource metadata providers into the shared root RuntimeConfig.Entities collection used by MCP.

This is a child investigation item for #3711. Please verify the runtime merge sequence, generated entity collection, and entity-to-data-source mappings across two or more child configurations.

Version

2.0.9

What database are you using?

Azure SQL

What hosting model are you using?

Local (including CLI)

Which API approach are you accessing DAB through?

MCP

Relevant log output

Startup completes with `Successfully completed runtime initialization`, but `tools/call` for `describe_entities` returns `NoEntitiesConfigured` after using a parent config with two or more child configs containing `autoentities`.

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