Fix 'is_merged' not being available on the Issue

[kasya]

The view issues page on the module level was failing after recent update to get rid of N +1.
This PR introduces a fix for that.

I also updated frontend representation of labels for issues that have merged PRs. They will now say Closed instead of Merged as Issue can not be merged. But it will show purple color for issue with merged PR and red for issue that was just closed - this matches GitHub representation.

Resolves #3841

Checklist

• Required: I followed the contributing workflow
• Required: I verified that my code works as intended and resolves the issue as described
• Required: I ran make check-test locally: all warnings addressed, tests passed
• I used AI for code, documentation, tests, or communication related to this PR

[coderabbitai]

Summary by CodeRabbit

• Refactor

  • Improved backend query performance for loading issue data by optimizing how merged pull requests are retrieved and prefetched alongside related information.

• Style

  • Updated issue status labels throughout the application to display "Closed" instead of "Merged" for consistency across all user-facing components.

Walkthrough

Replaced an Exists/OuterRef annotation with a module-level Prefetch (MERGED_PULL_REQUESTS_PREFETCH) for detecting merged pull requests in the Issue node; propagated that prefetch into mentorship issue queries; and updated frontend/UI and tests to display "Closed" (instead of "Merged") for merged issues.

Changes

Cohort / File(s)	Summary
Issue node (backend) backend/apps/github/api/internal/nodes/issue.py	Added MERGED_PULL_REQUESTS_PREFETCH (Prefetch of closed & merged PRs to merged_pull_requests), removed Exists/OuterRef imports/annotation, and refactored is_merged resolver to use pre-fetched merged_pull_requests.
Mentorship queries (backend) backend/apps/mentorship/api/internal/nodes/module.py, backend/apps/mentorship/api/internal/queries/mentorship.py	Imported and added MERGED_PULL_REQUESTS_PREFETCH to prefetch_related calls for issue lists and single-issue lookups to ensure merged_pull_requests is pre-fetched.
Frontend UI frontend/src/app/my/mentorship/programs/.../issues/[issueId]/page.tsx, frontend/src/components/IssuesTable.tsx	Changed displayed status label for merged issues from "Merged" to "Closed" (badge text only; styling/control flow preserved).
Frontend tests frontend/__tests__/unit/components/IssuesTable.test.tsx, frontend/__tests__/unit/pages/IssuesPage.test.tsx, frontend/__tests__/unit/pages/ModuleIssueDetailsPage.test.tsx	Updated assertions to expect "Closed" instead of "Merged" for cases where an issue is closed and isMerged is true.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• perf: optimize isMerged resolver using Prefetch #3764 — Reworked the is_merged implementation to address N+1 detection for merged pull requests (same backend area and intent).
• Unify issues view between module issues page and Mentee page #3050 — Changes to frontend handling/display of issue merged/closed state that overlap with the UI/test updates here.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title accurately captures the main issue: fixing the 'is_merged' attribute that became unavailable on the Issue model/resolver.
Description check	✅ Passed	The PR description is related to the changeset, explaining the N+1 query fix, the resolver issue, and the frontend label updates for merged/closed states.
Linked Issues check	✅ Passed	The PR fully addresses issue #3841 by replacing the Exists/OuterRef annotation with a Prefetch approach, making is_merged safe to resolve regardless of queryset path.
Out of Scope Changes check	✅ Passed	All changes are in-scope: backend optimization for is_merged resolution, frontend label text updates from 'Merged' to 'Closed', and corresponding test updates are all related to issue #3841.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix-accessing-issues-page

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No actionable comments were generated in the recent review. 🎉

🧹 Recent nitpick comments

backend/apps/github/api/internal/nodes/issue.py (1)

59-62: Minor: state="closed" filter is redundant.

A PR with merged_at__isnull=False is by definition closed (GitHub sets state to "closed" upon merge). The extra filter is harmless but adds no value. Keeping it as a defensive guard is acceptable.

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[cubic-dev-ai]

No issues found across 8 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.68%. Comparing base (152206e) to head (8e772a2).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
backend/apps/github/api/internal/nodes/issue.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3843      +/-   ##
==========================================
+ Coverage   90.24%   93.68%   +3.44%     
==========================================
  Files         463      463              
  Lines       14416    14420       +4     
  Branches     1937     1939       +2     
==========================================
+ Hits        13009    13509     +500     
+ Misses        988      535     -453     
+ Partials      419      376      -43     

Flag	Coverage Δ
backend	95.65% <75.00%> (+4.67%)	⬆️
frontend	88.17% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
[...Key]/modules/[moduleKey]/issues/[issueId]/page.tsx](https://app.codecov.io/gh/OWASP/Nest/pull/3843?src=pr&el=tree&filepath=frontend%2Fsrc%2Fapp%2Fmy%2Fmentorship%2Fprograms%2F%5BprogramKey%5D%2Fmodules%2F%5BmoduleKey%5D%2Fissues%2F%5BissueId%5D%2Fpage.tsx&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OWASP#diff-ZnJvbnRlbmQvc3JjL2FwcC9teS9tZW50b3JzaGlwL3Byb2dyYW1zL1twcm9ncmFtS2V5XS9tb2R1bGVzL1ttb2R1bGVLZXldL2lzc3Vlcy9baXNzdWVJZF0vcGFnZS50c3g=)	87.28% <100.00%> (ø)
frontend/src/components/IssuesTable.tsx	91.66% <ø> (ø)
backend/apps/github/api/internal/nodes/issue.py	89.28% <75.00%> (+0.39%)	⬆️

... and 46 files with indirect coverage changes

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[arkid15r]

👍