refactor(react-router): cache outlet child lookups

[Sheraff]

Note

i'm not convinced we need this. It does yield a stable 1% client-nav improvement at the cost of more code. There might be an architecture-driven solution that would benefit all 3 adapters:

1. add depth to each route definition, this is known at initialization
2. then you just need to look up that index in the matchIds array

Summary

• add a shared childMatchIdByRouteId derived store in the React router store factory
• have Outlet read the next child match from that store on both the client and server instead of scanning matchesId
• leave the local test addition out of this PR per request

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☁️ Nx Cloud last updated this comment at 2026-03-08 07:07:45 UTC

[github-actions]

Bundle Size Benchmarks

• Commit: 4ea2a62787d0
• Measured at: 2026-03-08T06:54:56.423Z
• Baseline source: history:4ea2a62787d0
• Dashboard: bundle-size history

Scenario	Current (gzip)	Delta vs baseline	Raw	Brotli	Trend
react-router.minimal	87.78 KiB	+960 B (+1.08%)	276.67 KiB	76.38 KiB	▁▁▁▁▁▃▃▃▃▃▃█
react-router.full	91.03 KiB	+1.15 KiB (+1.27%)	287.36 KiB	79.08 KiB	▁▁▁▁▁▂▂▂▂▂▂█
solid-router.minimal	35.26 KiB	-930 B (-2.51%)	106.65 KiB	31.64 KiB	▆▆▆▆▆██████▁
solid-router.full	39.73 KiB	-786 B (-1.90%)	120.25 KiB	35.58 KiB	▅▅▅▅▅██████▁
vue-router.minimal	53.06 KiB	+1.03 KiB (+1.98%)	152.02 KiB	47.59 KiB	▁▁▁▁▁▂▂▂▂▂▂█
vue-router.full	58.09 KiB	+1.24 KiB (+2.19%)	168.08 KiB	51.96 KiB	▁▁▁▁▁▂▂▂▂▂▂█
react-start.minimal	100.44 KiB	+1.03 KiB (+1.04%)	315.86 KiB	86.87 KiB	▁▁▁▁▁▃▃▃▃▃▃█
react-start.full	103.85 KiB	+1.07 KiB (+1.04%)	326.03 KiB	89.80 KiB	▁▁▁▁▁▂▂▂▂▂▂█
solid-start.minimal	47.58 KiB	-929 B (-1.87%)	144.28 KiB	42.07 KiB	▆▆▆▆▆██████▁
solid-start.full	53.20 KiB	-782 B (-1.42%)	160.78 KiB	46.84 KiB	▅▅▅▅▅██████▁

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

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commit: 18db703

[codspeed-hq]

Merging this PR will not alter performance

✅ 6 untouched benchmarks

---

_{Comparing opencode/react-outlet-child-store (0361303) with refactor-signals (4a410d8)}