feat: Add PolicyEngine.EvaluateAsync so external backends aren't forced into sync-over-async - #3778
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…c-over-async PolicyEngine only exposed a synchronous Evaluate that calls IExternalPolicyBackend.Evaluate, so backends whose work is async (a network call) had to block a thread with GetAwaiter().GetResult(). - Extract the shared prologue (Prepare) and result combination (Combine) from Evaluate. - Add PolicyEngine.EvaluateAsync(agentDid, context, ct) that awaits backends' EvaluateAsync; external backends are evaluated sequentially to preserve ordering. Internal (in-memory) policy evaluation and the fail-closed resolution are unchanged. - Sync Evaluate keeps its exact previous behavior. Adds tests that EvaluateAsync uses the backend async path (and Evaluate the sync path), plus async fail-closed on backend error. Refs microsoft#3775
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@microsoft-github-policy-service agree company="Amazon" |
Garrett Beatty (GarrettBeatty)
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Garrett Beatty (GarrettBeatty)
marked this pull request as ready for review
August 18, 2026 23:32
Garrett Beatty (GarrettBeatty)
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MohammadHaroonAbuomar and
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August 18, 2026 23:32
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Draft implementation for #3775.
Problem
PolicyEngineonly exposes a synchronousEvaluatethat callsIExternalPolicyBackend.Evaluate. A backend whose decision requires a network call (an async-only SDK) has to block a thread with.GetAwaiter().GetResult(), which pressures the thread pool under load.Change
Prepare: validate, snapshot, build context, run in-memory policies) and result combination (Combine: fail-closed resolution) out ofEvaluate.PolicyEngine.EvaluateAsync(agentDid, context, ct)that awaits each backend'sEvaluateAsync. External backends run sequentially to preserve ordering and avoid assuming they're concurrency-safe.Evaluatekeeps its exact previous behavior; internal policy evaluation and fail-closed semantics are unchanged.Tests
Adds coverage that
EvaluateAsyncuses the backend async path,Evaluateuses the sync path, andEvaluateAsyncstill fails closed on a backend error. All existing policy tests pass (146 total).Open questions for maintainers
GovernanceKernel.EvaluateToolCall(and the MCP decorator, which is alreadyasync)? Kept this PR to the engine to stay focused; happy to follow up.Draft: opening to align on shape before finalizing.