fix: avoid duplicate joins on errors

[SkArchon]

In case of non http errors the errors are duplicated resulting in duplicates in the error message such as

Post \"http://localhost:4001/graphql\": dial tcp [::1]:4001: connect: connection refused
Post \"http://localhost:4001/graphql\": dial tcp [::1]:4001: connect: connection refused
Failed to fetch from Subgraph 'employees'.

This is as we join the same error multiple times. Since we already join res.err and set it to l.ctx.subgraphErrors in l.mergeResult we can simply remove the join inside newResponseInfo

Summary by CodeRabbit

• Bug Fixes
  • Improved error reporting for subgraph responses by avoiding aggregation of multiple errors. Users will now see clearer, more precise error messages that better reflect the originating issue.
  • Reduces noisy or confusing error chains, improving consistency in error handling and making failures easier to diagnose in client applications and logs.

Checklist

• I have discussed my proposed changes in an issue and have received approval to proceed.
• I have followed the coding standards of the project.
• Tests or benchmarks have been added or updated.

[coderabbitai]

Walkthrough

Replaces joined error propagation in newResponseInfo by setting Err solely to subgraphError, removing the previous goerrors.Join(res.err, subgraphError) behavior.

Changes

Cohort / File(s)	Summary of Changes
Error handling update v2/pkg/engine/resolve/loader.go	In newResponseInfo, Err is now assigned to subgraphError directly instead of goerrors.Join(res.err, subgraphError), altering error propagation to exclude the parent error.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The title concisely summarizes the primary fix of preventing duplicate error joins and clearly reflects the main behavioral change in the code.

✨ Finishing touches

• 📝 Generate docstrings

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📜 Recent review details

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Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 0d60605 and 042dc24.

📒 Files selected for processing (1)

• v2/pkg/engine/resolve/loader.go (1 hunks)

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• GitHub Check: Build and test (go 1.25 / ubuntu-latest)
• GitHub Check: Build and test (go 1.25 / windows-latest)
• GitHub Check: Build and test (go 1.25 / windows-latest)
• GitHub Check: Build and test (go 1.25 / ubuntu-latest)

🔇 Additional comments (1)

v2/pkg/engine/resolve/loader.go (1)

66-92: Approve removal of redundant error join
All newResponseInfo invocations pass l.ctx.subgraphErrors, which already includes res.err, eliminating duplicate messages without losing any errors.

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[ysmolski]

Indeed, we call newResponseInfo after every mergeResult.