.NET: fix: synchronize StateManager for executors that run concurrently in a superstep

[RParnell-YB]

Motivation and Context

Fixes #8627.

InProcessRunner.RunSuperstepAsync delivers a superstep's messages to every receiving executor concurrently (one DeliverMessagesAsync task per receiver, awaited with Task.WhenAll), and each executor reaches the same StateManager through its bound IWorkflowContext. StateManager kept its queued updates in a plain Dictionary<UpdateKey, StateUpdate> and wrote it with no synchronisation, so two executors queueing state in the same superstep raced on it. In a production host this surfaced as

System.InvalidOperationException: Operations that change non-concurrent collections must have exclusive access.
A concurrent update was performed on this collection and corrupted its state. The collection's state is no longer correct.
   at System.Collections.Generic.Dictionary`2.TryInsert(...)
   at Microsoft.Agents.AI.Workflows.Execution.StateManager.WriteStateAsync(...)
   at Microsoft.Agents.AI.Workflows.InProc.InProcessRunnerContext.BoundWorkflowContext.QueueStateUpdateAsync(...)

when four fan-out roots finished within 14 ms of each other, reported as an executor handler failure attributed to no step. Silent corruption is the other possible outcome of the same race. Neither StateManager.cs nor InProcessRunner.cs changed between 1.21.0 and 1.22.0; #8252 fixed the Declarative package's WorkflowFormulaState, a different class.

Description

• One _syncRoot lock guards every access to _scopes and _queuedUpdates (GetOrCreateScope, the new TryGetScope, WriteStateAsync, both ClearStateAsync overloads, the queued-update lookup in ReadValueOrDefaultAsync, ExportStateAsync, ImportStateAsync).
• No lock spans an await. StateScope contents are only written by PublishUpdatesAsync and ImportStateAsync, which run between supersteps, so the awaiting StateScope.ReadStateAsync / ReadKeysAsync calls stay outside the lock.
• GetUpdatesForScopeStrict materialises its result under the lock instead of returning a lazy Where over Keys, so callers enumerate a snapshot while other executors keep queueing. ApplyUnpublishedUpdates and ClearStateAsync(ScopeId) consume the snapshot's values rather than re-indexing the dictionary.
• PublishUpdatesAsync takes the queued updates out under the lock and publishes the snapshot, so the clear is atomic with the read.
• ExportStateAsync and ImportStateAsync keep their existing "no queued updates" checks, now under the lock.

No public API change; StateManager is internal.

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

Test: StateManagerTests.Test_ConcurrentExecutors_QueueAndReadState_WithoutCorruptionAsync — 64 concurrent writers, 200 WriteStateAsync / ReadStateAsync / ReadKeysAsync round-trips each, then PublishUpdatesAsync, for a shared and a private scope; asserts every key and value survives and nothing is left queued. On main it fails 3 runs out of 3; with this change it passes. Microsoft.Agents.AI.Workflows.UnitTests (net10.0): 770 passed, 0 failed. dotnet format whitespace --verify-no-changes clean on both files.

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• Preserve queued updates when aggregation or publication fails · New

What changed in this PR

Synchronizes .NET workflow state access during concurrent executor execution.

Changes:

• Adds locking and snapshot-based state update handling.
• Adds concurrent shared/private scope tests.

File	Description
StateManager.cs	Synchronizes state dictionaries and publication.
StateManagerTests.cs	Tests concurrent state writes and reads.

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[Vincent Biret (baywet)]

Thanks for the contribution!

[Vincent Biret (baywet)]

why can't we use concurrent dictionaries instead of regular ones, and do away with all the locks?