.NET: Fix JSON arrays of objects parsed as empty records when no schema is defined

[LEDazzio01]

Motivation and Context

Fixes #4195 — JSON arrays of objects are parsed as empty records when no schema is defined in declarative workflows.

When an InvokeAzureAgent action returns a JSON object containing an array of objects, and the output is captured via responseObject, all nested object properties are silently dropped. Each object in the array becomes {}. Subsequent Foreach iteration over the array crashes with an unhandled workflow failure.

Description

Root cause: In JsonDocumentExtensions.cs, the ParseTable method's DetermineElementType() function creates a schema-bound VariableType with an empty (non-null) schema when targetType.Schema is null:

// Before (broken)
JsonValueKind.Object => VariableType.Record(targetType.Schema?.Select(kvp => (kvp.Key, kvp.Value)) ?? []),

When targetType.Schema is null, the ?? [] fallback passes an empty collection to VariableType.Record(), creating a VariableType with Schema set to an empty FrozenDictionary (non-null, count = 0). Downstream, ParseRecord checks targetType.Schema is null and takes the ParseSchema path (which iterates over zero fields), silently discarding all JSON properties.

Fix: Check targetType.HasSchema (which correctly handles empty schemas) and fall back to VariableType.RecordType when no schema is defined:

// After (fixed)
JsonValueKind.Object => targetType.HasSchema
    ? VariableType.Record(targetType.Schema!.Select(kvp => (kvp.Key, kvp.Value)))
    : VariableType.RecordType,

This ensures ParseRecord takes the dynamic ParseValues() path that preserves all JSON properties.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? No — this is a bug fix that restores expected behavior.

[LEDazzio01]

I have sole ownership of intellectual property rights to my Submissions and I am not making Submissions in the course of work for my employer.

[Copilot]

Pull request overview

Fixes a declarative workflow JSON parsing bug where arrays of objects could be inferred as “empty-schema records,” causing nested object properties to be dropped when no schema is defined.

Changes:

• Updates ParseTable element-type inference to use VariableType.RecordType when the target list type has no schema, avoiding creation of an empty (non-null) schema.
• Uses targetType.HasSchema to decide when to propagate a schema into inferred record element types.

[Copilot]

Add a regression unit test for the schema-less path this fixes: parsing a JSON object (using VariableType.RecordType) that contains an array of objects should preserve nested object properties (e.g., { "items": [ {"name":"Alice"} ] } should yield dictionaries with a name key). Current unit tests cover record parsing without schema, and arrays of records with an explicit schema, but not arrays of objects when the array element type must be inferred with no schema (the scenario that previously produced {} elements).

[crickman]

@LEDazzio01 - I agree that a unit-test would be a great way to demonstrate the fix. A unit-test fixture already exists here: https://github.com/microsoft/agent-framework/blob/main/dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/Extensions/JsonDocumentExtensionsTests.cs

AI might be able to quickly add a unit-test. I'm confident we can get this merged as soon as the test is ready.

[LEDazzio01]

I'll add the unit test when I get home from work late this afternoon :)