fix(router-core): don't set isServer if NODE_ENV test

[schiller-manuel]

Summary by CodeRabbit

• Bug Fixes
  • Server-side detection now correctly returns undefined in test environments instead of always returning a fixed value, improving test accuracy.

[coderabbitai]

Caution

Review failed

The pull request is closed.

📝 Walkthrough

Walkthrough

The isServer export in packages/router-core/src/isServer/server.ts is modified from a constant boolean to a conditional value that evaluates to true in non-test environments and undefined when NODE_ENV is 'test', introducing environment-aware behavior.

Changes

Cohort / File(s)	Summary
Environment-aware isServer detection packages/router-core/src/isServer/server.ts	Changed isServer from a fixed boolean constant to a conditional expression that returns true or undefined based on NODE_ENV, enabling test-specific behavior.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• fix: avoid destructuring internal server property in interpolatePath #6580: Related change to server/isServer logic in packages/router-core that modifies how interpolatePath handles the server property.

Suggested reviewers

• Sheraff

Poem

🐰 A little bunny hops with glee,
Testing truthfully, setting servers free!
When NODE_ENV says "test," undefined flows,
But truth remains where production goes. ✨

✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch isServer-test-undefined

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[nx-cloud]

View your CI Pipeline Execution ↗ for commit cc299f7

Command	Status	Duration	Result
nx run tanstack-router-e2e-bundle-size:build --...	✅ Succeeded	1m 25s	View ↗

---

☁️ Nx Cloud last updated this comment at 2026-02-21 21:58:21 UTC

[github-actions]

Bundle Size Benchmarks

• Commit: a21eab71136a
• Measured at: 2026-02-21T21:44:29.663Z
• Baseline source: history:996e18284413
• Dashboard: bundle-size history

Scenario	Current (gzip)	Delta vs baseline	Raw	Brotli	Trend
react-router.minimal	86.76 KiB	0 B (0.00%)	272.72 KiB	75.41 KiB	▅▅▅
react-router.full	89.85 KiB	0 B (0.00%)	283.19 KiB	78.06 KiB	▅▅▅
solid-router.minimal	36.04 KiB	0 B (0.00%)	107.87 KiB	32.43 KiB	▅▅▅
solid-router.full	40.39 KiB	0 B (0.00%)	120.96 KiB	36.25 KiB	▅▅▅
vue-router.minimal	51.90 KiB	0 B (0.00%)	147.86 KiB	46.62 KiB	▅▅▅
vue-router.full	56.76 KiB	0 B (0.00%)	163.47 KiB	50.98 KiB	▅▅▅
react-start.minimal	99.25 KiB	0 B (0.00%)	311.71 KiB	85.93 KiB	▅▅▅
react-start.full	102.66 KiB	0 B (0.00%)	321.63 KiB	88.71 KiB	▅▅▅
solid-start.minimal	48.28 KiB	0 B (0.00%)	145.30 KiB	42.70 KiB	▅▅▅
solid-start.full	53.76 KiB	0 B (0.00%)	161.25 KiB	47.34 KiB	▅▅▅

Trend sparkline is historical gzip bytes ending with this PR measurement; lower is better.

[pkg-pr-new]

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commit: cc299f7