fix: propagate error in ArrayNode output gathering

[Sanchit2662]

Summary

This PR fixes a silent error propagation bug in the ArrayNode worker output-gathering path (flytepropeller/pkg/controller/nodes/array/worker.go).
Due to a hardcoded nil being returned on the response channel, errors encountered while reading sub-node outputs were silently discarded, leading to workflows completing successfully with missing or corrupted outputs.

This is a one-character fix that restores correct error propagation and aligns the behavior with the existing node execution handling logic.

---

Fix

Return the actual captured error instead of hardcoding nil:

// After
gatherOutputsRequest.responseChannel <- struct {
    literalMap map[string]*idlcore.Literal
    error
}{literalMap, err}

This mirrors the already-correct behavior used for nodeExecutionRequest earlier in the same worker loop and ensures consistent error handling.

---

Impact

Before

• Output read failures silently ignored
• Workflows succeed with incorrect or missing data
• Downstream task behavior becomes nondeterministic
• Production issues are extremely difficult to diagnose

After

• Output gathering errors are properly propagated
• Workflows fail explicitly and predictably
• Retry / failure semantics behave as expected
• No silent data corruption

This affects all Flyte deployments using ArrayNodes, which is a core execution primitive.

---

How was this patch tested?

• Manually verified error propagation path by inducing output read failures
• Confirmed consistency with nodeExecutionRequest error handling logic
• Ensured workerErrorCollector correctly captures and reports the error after the fix

No new tests were added due to the minimal and localized nature of the change, but the behavior now matches the established and already-tested execution path.

---

Labels

• fixed

---

Checklist

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

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[Sanchit2662]

Hi @machichima ,
This pr fixes a bug where ArrayNode output-gathering errors were silently swallowed, causing workflows to succeed with missing outputs.
Whenever you have time, I’d really appreciate it if you could take a look and review the PR.
Thank you!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.95%. Comparing base (575c0af) to head (26ab08e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6860      +/-   ##
==========================================
- Coverage   56.96%   56.95%   -0.01%     
==========================================
  Files         929      929              
  Lines       58152    58152              
==========================================
- Hits        33125    33120       -5     
- Misses      21985    21990       +5     
  Partials     3042     3042              

Flag	Coverage Δ
unittests-datacatalog	53.51% <ø> (ø)
unittests-flyteadmin	53.10% <ø> (-0.04%)	⬇️
unittests-flytecopilot	43.06% <ø> (ø)
unittests-flytectl	64.00% <ø> (ø)
unittests-flyteidl	75.71% <ø> (ø)
unittests-flyteplugins	60.13% <ø> (ø)
unittests-flytepropeller	53.63% <100.00%> (ø)
unittests-flytestdlib	63.29% <ø> (+0.02%)	⬆️

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[machichima]

Hi @Sanchit266,
Thank you for the fix! Do you mind providing result screenshot showing the error is raised correctly?

[machichima]

LGTM

[Sanchit2662]

Hi @machichima,

I verified this locally by simulating the case where a subnode is marked Succeeded
but its output file is missing.

Running:
go clean -testcache && go test -v -run "TestHandleArrayNodePhaseSucceeding/Success$" .

Now results in:
worker error(s) encountered: [0]: failed to read data from
s3://bucket/output/0/0/outputs.pb: file does not exist

This confirms the output read error is correctly propagated instead of being
silently ignored. The test failure is expected in this setup since outputs are missing.

[machichima]

Thanks @Sanchit2662!
Could you also add a test here (like what you modified in TestHandleArrayNodePhaseSucceeding) to make sure the error is raised?
Thank you!