Allow Vars in page metadata

[harsh21234i]

Fixes #6923.

@rx.page evaluated State Vars for title and description as Python
booleans, raising VarTypeError. Dynamic descriptions could also fail during
metadata compilation.

Changes

• Allow str | Var | None for @rx.page metadata.
• Replace Var-unsafe truthiness checks with explicit is not None checks.
• Fix dynamic metadata handling for 404 pages.
• Add regression tests for decorator, compiler, and 404 metadata paths.
• Add a bugfix news fragment.

Testing

• Focused unit tests: 205 passed, 1 skipped
• Ruff format: passed
• Ruff lint: passed
• git diff --check: passed

[cubic-dev-ai]

No issues found across 7 files

_{Re-trigger cubic}

[greptile-apps]

Greptile Summary

The PR allows reactive Vars in page titles and descriptions while avoiding Var-unsafe truthiness evaluation.

• Widens page metadata types through decorator, registration, and compiler boundaries.
• Preserves supplied Vars and empty-string values using explicit None checks.
• Adds regression coverage for decorator, compiler, and 404 metadata paths.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
reflex/page.py	Accepts title and description Vars and preserves all explicitly supplied values without evaluating their truthiness.
reflex/app.py	Updates 404 metadata fallback behavior to default only when title or description is absent.
reflex/compiler/utils.py	Carries Vars into title and description components using their supported child and prop contracts.
tests/units/test_page.py	Verifies the page decorator preserves reactive title and description Vars.
tests/units/test_app.py	Verifies 404 preparation does not evaluate or replace supplied metadata Vars.
tests/units/compiler/test_compiler.py	Verifies a reactive description is retained as the Description component's content Var.

_{Reviews (2): Last reviewed commit: "Merge upstream main into page metadata f..." | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

✅ 27 untouched benchmarks
⏩ 8 skipped benchmarks¹

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_{Comparing harsh21234i:fix/6923-dynamic-page-meta (efefbd2) with main (d86f167)}

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. ↩