Stop stripping frontend_path twice when matching routes

[JohannesGezachew]

closes #7090

What

get_router stripped frontend_path from every path it matched, but its two callers pass different kinds of paths:

• The event handler in app.py matches router_data["pathname"], which the frontend sends relative to frontend_path (see the comment in state.js). With frontend_path="/app", /apple became le and resolved to 404, and /app became / and resolved to the index page.
• OnLoadInternalState.on_load_internal passes self.router.url.path, which is the browser URL and does include frontend_path. This is why the strip was added to the matcher in fix various issues with frontend_path #5698.

The router now always matches paths relative to frontend_path, and App.get_load_events strips frontend_path from the URL path itself. It strips it only as a whole path segment, so /app/apple still maps to apple, and a URL outside frontend_path such as /apple still gets the 404 load events. The matcher cache is now keyed on the path alone.

Tests

Added to tests/units/test_route.py:

• test_get_router_ignores_frontend_path: with frontend_path="/app", /apple, /app and / match apple, app and index. On current main the first two fail.

• test_get_load_events_strips_frontend_path: /app, /app/, /app/apple and /app/app resolve to the right page's load events, and /apple falls back to 404.

• tests/units/test_route.py: 43 passed.

• tests/units: 8466 passed. The 207 failures locally are all under tests/units/reflex_cli/v2/ and match what I see on main without this change.

Checklist

• Bug fix (non-breaking change which fixes an issue)
• Followed CONTRIBUTING.md; no other open PR for this change
• Added a news fragment
• ruff check, ruff format --check and pyright pass on the changed files

[cubic-dev-ai]

All reported issues were addressed across 4 files

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[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge; the previously reported out-of-prefix routing defect is fully fixed and covered by a regression test.

Summary

This PR makes route matching consistently operate on paths relative to frontend_path.

• Moves browser URL prefix validation and stripping into App.get_load_events.
• Rejects browser paths outside the configured frontend prefix.
• Removes duplicate prefix stripping and configuration-dependent cache keys from get_router.
• Adds regression coverage for prefixed routes, similarly named routes, the index route, and out-of-prefix URLs.
• Adds a user-facing bugfix news fragment.

_{Reviews (2) · Last reviewed commit: "Return 404 load events for URLs outside ..."}

[codspeed]

Merging this PR will not alter performance

✅ 40 untouched benchmarks
⏩ 8 skipped benchmarks¹

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_{Comparing JohannesGezachew:fix-frontend-path-double-strip (9ccab2e) with main (2f63cb3)}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[cubic-dev-ai]

All reported issues were addressed across 2 files (changes from recent commits).

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