[CELEBORN-2412] Propagate the worker error message through cpp MessageDispatcher failures

[yugan95]

What changes were proposed in this pull request?

MessageDispatcher::read decodes the error string a worker sends back on RPC_FAILURE / CHUNK_FETCH_FAILURE and then throws it away — both paths fulfil the pending promise with a blank std::exception():

holder.msgPromise.setException(folly::exception_wrapper(std::exception()));

This PR builds the exception from the message instead:

• RPC_FAILURE → folly::make_exception_wrapper<std::runtime_error>(failure->errorMsg())
• CHUNK_FETCH_FAILURE → same, using the already-formatted errorMsg that includes the streamChunkSlice context.

MessageDispatcherTest is strengthened accordingly: a shared takeExceptionMessage() helper is added, the two failure tests now assert on the message content rather than merely hasException(), and sendPushDataAndReceiveFailure uses a real StatusCode name (PUSH_DATA_FAIL_PARTITION_NOT_FOUND) so it exercises the classification path it is meant to protect.

Why are the changes needed?

ShuffleClientImpl::getPushDataFailCause classifies a push failure by matching StatusCode names as substrings of the error message, and PushDataCallback::onFailure / PushMergedDataCallback feed it exception->what(). With a blank std::exception, what() is a fixed runtime string that matches none of the 13 candidate causes, so classification always falls through to PUSH_DATA_FAIL_NON_CRITICAL_CAUSE. Two consequences:

1. excludeWorkerByCause only acts on the connection-fail / timeout causes and hits its default: branch every time, so celeborn.client.excludeWorker.enabled never actually excludes a worker on the C++ push path.
2. When revive attempts are exhausted, classifyPushFailure raises "PUSH_DATA_FAIL_NON_CRITICAL_CAUSE: <blank>" — the worker's real reason (partition not found, worker excluded, replica write failure, …) is gone from the task-failure message, which makes these failures very hard to diagnose from client logs alone.

Chunk fetch failures lose the worker's diagnostics the same way.

This restores parity with the Java client, where TransportResponseHandler surfaces the worker's error text and ShuffleClientImpl#getPushDataFailCause can act on it.

Does this PR resolve a correctness bug?

• Yes

Shuffle output is unaffected, so this is not a result-correctness bug. It is a failure-classification bug: worker exclusion never engages on the C++ push path, and the worker's reason is missing from the task-failure message.

Does this PR introduce any user-facing change?

• Yes

No config, API or behaviour change. Push and fetch failure messages now carry the worker's reason instead of a placeholder.

How was this patch tested?

Unit tests in cpp/celeborn/network/tests/MessageDispatcherTest.cpp:

• sendRpcRequestAndReceiveFailure — asserts the RPC failure message reaches the caller.
• sendPushDataAndReceiveFailure — asserts a StatusCode name (PUSH_DATA_FAIL_PARTITION_NOT_FOUND) survives on the exception, which is exactly what getPushDataFailCause needs to see.

Covered by the Celeborn Cpp Integration Test workflow (Run Unittests of Celeborn Cpp).

[Copilot]

Pull request overview

This PR improves the C++ client’s observability and failure classification by propagating worker-provided error strings through MessageDispatcher failures (instead of fulfilling promises with a blank std::exception()), and strengthens unit tests to assert on the surfaced message content.

Changes:

• Wrap RPC_FAILURE and CHUNK_FETCH_FAILURE with std::runtime_error containing the worker’s error message (and chunk context for fetch failures).
• Strengthen MessageDispatcherTest to assert that failure futures contain the expected error text (including a real StatusCode name substring for push failures).
• Add a shared helper to extract exception messages from failed futures.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
cpp/celeborn/network/MessageDispatcher.cpp	Preserve worker error text by setting promise exceptions with std::runtime_error messages for RPC and chunk-fetch failures.
cpp/celeborn/network/tests/MessageDispatcherTest.cpp	Add helper + tighten failure tests to validate exception message contents.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[SteNicholas]

LGTM.

[RexXiong]

LGTM

[SteNicholas]

LGTM.

[SteNicholas]

Merged to main(v1.0.0) and branch-0.7(v0.7.1).