The break

main currently does not compile, and its own Build and Test CI run is red. This blocks PR #1484 and every other PR, because they inherit the broken main when they merge it.

The error comes from src/ModelContextProtocol.Core/Server/AIFunctionMcpServerTool.cs, inside BuildLegacyWireProtocolTool():

AIFunctionMcpServerTool.cs(265,13): error CS0117: 'Tool' does not contain a definition for 'Execution'
AIFunctionMcpServerTool.cs(265,38): error CS1061: 'Tool' does not contain a definition for 'Execution'

across all target frameworks (net10.0/net9.0/net8.0/netstandard2.0). Because TreatWarningsAsErrors=true, the build fails outright.

Root cause — a semantic (logical) merge conflict

• The SEP-2663 Tasks Extension PR (Implement SEP-2663 Tasks Extension #1579, commit dbb7a20) intentionally removed the entire old Tool.Execution / ToolExecution surface (task support moved to the new Tasks capability). The removal is baselined in src/ModelContextProtocol.Core/CompatibilitySuppressions.xml.
• The SEP-2106 outputSchema PR (Relax outputSchema to any JSON Schema 2020-12 document per SEP-2106 #1568, commit 0663b7c8, the current main tip) added BuildLegacyWireProtocolTool(), which clones the Tool and copies every property — including the now-removed Execution. Relax outputSchema to any JSON Schema 2020-12 document per SEP-2106 #1568 was based on an older main that still had Tool.Execution.

When #1568 merged on top of #1579, the result was a semantic merge conflict: a dangling Execution = ProtocolTool.Execution, line referencing a property that no longer exists. No textual git conflict was raised, so it merged red.

The fix

Remove the single dangling line from the object initializer in BuildLegacyWireProtocolTool():

             Annotations = ProtocolTool.Annotations,
-            Execution = ProtocolTool.Execution,
             Icons = ProtocolTool.Icons,
             Meta = ProtocolTool.Meta,

Tool.Execution is not re-added — its removal was the intentional SEP-2663 design, and re-adding it would resurrect a deliberately-removed API and break the compatibility baseline. A full src/ grep confirms no other compiled references to a .Execution member on Tool or to the removed ToolExecution type remain (the only remaining hits are the CompatibilitySuppressions.xml baseline entries and unrelated names like ExecutionContext / TryGetOuterToolExecutionActivity).

Verification

• dotnet build -c Debug — succeeds for all target frameworks, 0 warnings / 0 errors.
• SEP-2106 legacy-wire back-compat tests (Sep2106ListToolsBackCompatTests, which exercise BuildLegacyWireProtocolTool) — 21/21 pass.
• Full tests/ModelContextProtocol.Tests (net10.0) — all 2070 non-environment tests pass. The only failures are pre-existing, environment-dependent tests unrelated to this change (stdio tests that spawn TestServer.exe, which isn't on PATH here, and a Docker-dependent test).

This unblocks PR #1484 and all other PRs by getting main green again.