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.NET: Fix stream reconnection for A2AAgent#5275

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SergeyMenshykh merged 3 commits intomicrosoft:a2a-agent-migrationfrom
SergeyMenshykh:fix-stream-reconnection
Apr 15, 2026
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.NET: Fix stream reconnection for A2AAgent#5275
SergeyMenshykh merged 3 commits intomicrosoft:a2a-agent-migrationfrom
SergeyMenshykh:fix-stream-reconnection

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@SergeyMenshykh SergeyMenshykh commented Apr 15, 2026 •
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Summary

When reconnecting to a completed A2A task via SubscribeToTask, the server returns UnsupportedOperation per A2A spec §3.3.2. This PR handles that by falling back to GetTaskAsync, so RunStreamingAsync with a continuation token always returns a result - even if the task completed while disconnected.

Changes

  • Add SubscribeToTaskWithFallbackAsync - catches UnsupportedOperation and falls back to GetTaskAsync
  • Populate ContinuationToken on streaming updates so callers can capture it for reconnection
  • Add warning log for the fallback path
  • Add A2AAgent_StreamReconnection sample
  • Fix A2AAgent_PollingForTaskCompletion to set AllowBackgroundResponses = true
  • Add unit tests for the fallback (success, session update, error propagation)

@SergeyMenshykh
Add SSE stream reconnection support to A2AAgent
7b9da47 
Implement automatic reconnection for SSE streams that disconnect mid-task,
using the Last-Event-ID header to resume from where the stream left off.

Changes:
- Add InvokeStreamingWithReconnectAsync method to A2AAgent with configurable
  max retries and delay between attempts
- Add new log messages for reconnection events
- Add A2AAgent_StreamReconnection sample demonstrating the feature
- Update existing polling sample to use simplified SendMessageAsync API
- Add unit tests for stream reconnection logic

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot AI review requested due to automatic review settings April 15, 2026 13:11
@SergeyMenshykh SergeyMenshykh changed the base branch from main to a2a-agent-migration April 15, 2026 13:11
@SergeyMenshykh SergeyMenshykh changed the title Add SSE stream reconnection support to A2AAgent .NET: Add SSE stream reconnection support to A2AAgent Apr 15, 2026
@SergeyMenshykh SergeyMenshykh self-assigned this Apr 15, 2026
@SergeyMenshykh SergeyMenshykh moved this to In Review in Agent Framework Apr 15, 2026
@SergeyMenshykh SergeyMenshykh changed the title .NET: Add SSE stream reconnection support to A2AAgent .NET: Fix stream reconnection for A2AAgent Apr 15, 2026
Copilot AI reviewed Apr 15, 2026
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Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds handling for streaming edge-cases in the A2A agent and updates samples/tests to demonstrate and validate reconnection/continuation behavior.

Changes:

  • Add SubscribeToTaskWithFallbackAsync to fall back to GetTaskAsync when subscribing to a terminal task returns UnsupportedOperation
  • Add structured logging for the fallback path
  • Add/update samples and tests around continuation tokens and (re)connecting to streaming responses

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file
File Description
dotnet/src/Microsoft.Agents.AI.A2A/A2AAgent.cs Adds Subscribe-to-task fallback to GetTask + propagates continuation token on updates
dotnet/src/Microsoft.Agents.AI.A2A/A2AAgentLogMessages.cs Adds a warning log for SubscribeToTask → GetTask fallback
dotnet/tests/Microsoft.Agents.AI.A2A.UnitTests/A2AAgentTests.cs Adds tests + stub behavior for UnsupportedOperation and GetTask failure paths
dotnet/samples/02-agents/A2A/README.md References the new stream reconnection sample
dotnet/samples/02-agents/A2A/A2AAgent_StreamReconnection/* New sample + documentation for stream reconnection using continuation tokens
dotnet/samples/02-agents/A2A/A2AAgent_PollingForTaskCompletion/Program.cs Uses AllowBackgroundResponses to force continuation tokens
dotnet/agent-framework-dotnet.slnx Adds the new sample project to the solution

Comment thread dotnet/samples/02-agents/A2A/A2AAgent_StreamReconnection/Program.cs
Comment thread dotnet/src/Microsoft.Agents.AI.A2A/A2AAgent.cs
Comment thread dotnet/tests/Microsoft.Agents.AI.A2A.UnitTests/A2AAgentTests.cs
Comment thread dotnet/samples/02-agents/A2A/A2AAgent_StreamReconnection/Program.cs Outdated
@moonbox3 moonbox3 added documentation Improvements or additions to documentation .NET labels Apr 15, 2026
SergeyMenshykh and others added 2 commits April 15, 2026 14:41
@SergeyMenshykh
address comments
d4fcbca
@SergeyMenshykh
Address PR review feedback
31c0a3b 
- Dispose SSE enumerator before GetTaskAsync fallback to release HTTP connection
- Wrap StreamWriter in using blocks with leaveOpen:true and explicit UTF-8 encoding
- Print update.Text instead of update object in stream reconnection sample

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@SergeyMenshykh SergeyMenshykh merged commit 6ad9279 into microsoft:a2a-agent-migration Apr 15, 2026
2 checks passed
@github-project-automation github-project-automation Bot moved this from In Review to Done in Agent Framework Apr 15, 2026
This was referenced Apr 22, 2026
Closed
Merged
moonbox3 pushed a commit to moonbox3/agent-framework that referenced this pull request Apr 23, 2026
@SergeyMenshykh
.NET: [Breaking] Migrate A2A agent and hosting to A2A SDK v1 (microso…
66e02c1 
…ft#5423)

* update a2a agent to the latest a2a sdk (microsoft#5257)

* Move A2A samples from 04-hosting to 02-agents (microsoft#5267)

Move the A2A sample projects (A2AAgent_AsFunctionTools and
A2AAgent_PollingForTaskCompletion) from samples/04-hosting/A2A/ to
samples/02-agents/A2A/ to better align with the sample directory
structure. Update solution file and samples README accordingly.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* .NET: Fix stream reconnection for A2AAgent (microsoft#5275)

* Add SSE stream reconnection support to A2AAgent

Implement automatic reconnection for SSE streams that disconnect mid-task,
using the Last-Event-ID header to resume from where the stream left off.

Changes:
- Add InvokeStreamingWithReconnectAsync method to A2AAgent with configurable
  max retries and delay between attempts
- Add new log messages for reconnection events
- Add A2AAgent_StreamReconnection sample demonstrating the feature
- Update existing polling sample to use simplified SendMessageAsync API
- Add unit tests for stream reconnection logic

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* address comments

* Address PR review feedback

- Dispose SSE enumerator before GetTaskAsync fallback to release HTTP connection
- Wrap StreamWriter in using blocks with leaveOpen:true and explicit UTF-8 encoding
- Print update.Text instead of update object in stream reconnection sample

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* .NET: Use IA2AClientFactory to create A2AClient (microsoft#5277)

* Refactor A2A extensions to use IA2AClientFactory and add ProtocolSelection sample

- Update A2AAgentCardExtensions to accept IA2AClientFactory instead of A2AClientOptions
- Update A2ACardResolverExtensions to accept IA2AClientFactory
- Update A2AClientExtensions to accept IA2AClientFactory
- Update A2AAgent to use IA2AClientFactory for client creation
- Add A2AAgent_ProtocolSelection sample demonstrating protocol selection
- Add comprehensive unit tests for all changes
- Update README files with new sample reference

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Reorder params: options before loggerFactory in A2A extensions

Move A2AClientOptions parameter before ILoggerFactory in AsAIAgent
and GetAIAgentAsync extension methods to follow the repo convention
of keeping LoggerFactory and CancellationToken as the last parameters.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* .NET: Migrate A2A hosting to A2A SDK v1 (microsoft#5363)

* .NET: Migrate A2A hosting to A2A SDK v1

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* remove unused agent card

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* .NET: Split A2A endpoint mapping into protocol-specific methods (microsoft#5413)

* .NET: Refactor A2A hosting registration into A2AServerServiceCollectionExtensions

- Rename A2AHostingOptions to A2AServerRegistrationOptions
- Move server registration logic from A2AEndpointRouteBuilderExtensions
  and AIAgentExtensions into new A2AServerServiceCollectionExtensions
- Remove A2AProtocolBinding and AIAgentExtensions (consolidated)
- Update samples and tests to use the new registration API

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* address copilot comments

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Remove unnecessary using directive in AgentWebChat.AgentHost

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* restore AsyncEnumerable package version

* address copilot initial feedback

* address automated code review and formatting issues

* fix formatting issues

* Add DI wiring verification tests for AddA2AServer

Add three tests to A2AServerServiceCollectionExtensionsTests that verify
custom keyed services are actually wired through to the A2AServer, not
just that the server resolves non-null:

- Custom IAgentHandler: verifies the keyed handler is invoked when
  processing a SendMessageRequest instead of the default A2AAgentHandler.
- Custom AgentSessionStore (no handler): verifies the keyed session
  store's GetSessionAsync is called during request processing when no
  custom handler is registered.
- Default stores end-to-end: verifies the InMemoryAgentSessionStore and
  InMemoryTaskStore defaults successfully process a request. Uses a new
  CreateAgentMockForRequests helper that includes SerializeSessionCoreAsync
  setup needed by InMemoryAgentSessionStore.

All tests call A2AServer.SendMessageAsync directly (no HTTP layer needed)
and use CancellationToken timeouts to guard against hangs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
pull Bot pushed a commit to TheTechOddBug/agent-framework that referenced this pull request Apr 23, 2026
@SergeyMenshykh
.NET: Add streaming support to A2A agent handler (microsoft#5427)
0dbcc9f 
* update a2a agent to the latest a2a sdk (microsoft#5257)

* Move A2A samples from 04-hosting to 02-agents (microsoft#5267)

Move the A2A sample projects (A2AAgent_AsFunctionTools and
A2AAgent_PollingForTaskCompletion) from samples/04-hosting/A2A/ to
samples/02-agents/A2A/ to better align with the sample directory
structure. Update solution file and samples README accordingly.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* .NET: Fix stream reconnection for A2AAgent (microsoft#5275)

* Add SSE stream reconnection support to A2AAgent

Implement automatic reconnection for SSE streams that disconnect mid-task,
using the Last-Event-ID header to resume from where the stream left off.

Changes:
- Add InvokeStreamingWithReconnectAsync method to A2AAgent with configurable
  max retries and delay between attempts
- Add new log messages for reconnection events
- Add A2AAgent_StreamReconnection sample demonstrating the feature
- Update existing polling sample to use simplified SendMessageAsync API
- Add unit tests for stream reconnection logic

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* address comments

* Address PR review feedback

- Dispose SSE enumerator before GetTaskAsync fallback to release HTTP connection
- Wrap StreamWriter in using blocks with leaveOpen:true and explicit UTF-8 encoding
- Print update.Text instead of update object in stream reconnection sample

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* .NET: Use IA2AClientFactory to create A2AClient (microsoft#5277)

* Refactor A2A extensions to use IA2AClientFactory and add ProtocolSelection sample

- Update A2AAgentCardExtensions to accept IA2AClientFactory instead of A2AClientOptions
- Update A2ACardResolverExtensions to accept IA2AClientFactory
- Update A2AClientExtensions to accept IA2AClientFactory
- Update A2AAgent to use IA2AClientFactory for client creation
- Add A2AAgent_ProtocolSelection sample demonstrating protocol selection
- Add comprehensive unit tests for all changes
- Update README files with new sample reference

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Reorder params: options before loggerFactory in A2A extensions

Move A2AClientOptions parameter before ILoggerFactory in AsAIAgent
and GetAIAgentAsync extension methods to follow the repo convention
of keeping LoggerFactory and CancellationToken as the last parameters.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* .NET: Migrate A2A hosting to A2A SDK v1 (microsoft#5363)

* .NET: Migrate A2A hosting to A2A SDK v1

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* remove unused agent card

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* .NET: Split A2A endpoint mapping into protocol-specific methods (microsoft#5413)

* .NET: Refactor A2A hosting registration into A2AServerServiceCollectionExtensions

- Rename A2AHostingOptions to A2AServerRegistrationOptions
- Move server registration logic from A2AEndpointRouteBuilderExtensions
  and AIAgentExtensions into new A2AServerServiceCollectionExtensions
- Remove A2AProtocolBinding and AIAgentExtensions (consolidated)
- Update samples and tests to use the new registration API

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* address copilot comments

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Remove unnecessary using directive in AgentWebChat.AgentHost

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* restore AsyncEnumerable package version

* address copilot initial feedback

* address automated code review and formatting issues

* fix formatting issues

* Add streaming support to A2A agent handler

Add HandleNewMessageStreamingAsync to A2AAgentHandler that routes
StreamingResponse requests through RunStreamingAsync, enqueuing an A2A
Message for each AgentResponseUpdate.

Add MessageConverter.ToParts(AgentResponseUpdate) extension to convert
streaming update contents to A2A Parts with unsupported-content filtering.

Add CreateMessageFromUpdate to map AgentResponseUpdate to A2A Message.

Add 16 new tests covering the streaming path and converter.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Add streaming edge-case tests for A2AAgentHandler

Add two tests covering gaps in the streaming path:

- ExecuteAsync_Streaming_WhenNoUpdates_EnqueuesNoMessagesAndSavesSessionAsync:
  Verifies that when RunStreamingAsync yields an empty async enumerable,
  no messages are enqueued and only SaveSessionAsync runs.

- ExecuteAsync_Streaming_CancellationTokenIsPropagatedToRunStreamingAsyncAsync:
  Verifies that the CancellationToken from ExecuteAsync is propagated
  through to the inner agent's RunCoreStreamingAsync call.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* address copilot comments

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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@westey-m westey-m westey-m approved these changes

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