Fix Python 3.14 event handler annotation resolution

[harsh21234i]

Summary

Fixes #6890.

Python 3.14 evaluates deferred method annotations using the owning class
namespace. Runtime attributes on a state class can therefore shadow builtin
annotation names such as dict.

This caused valid handlers like:

def on_event(self, event: dict):
...

to fail during event argument validation.

Changes

• Cache annotations for state-bound event handlers before runtime class patches.
• Use cached annotations for event and upload-handler validation.
• Preserve partial-handler support and unresolved forward-reference fallback.
• Avoid eager annotation resolution for unbound synthetic handlers.
• Add Python 3.14 regression coverage.
• Add changelog fragments.

Testing

• Python 3.14 regression test passed
• tests/units/test_event.py: 107 passed
• Ruff check passed
• Ruff format passed
• Diff check passed

[harsh21234i]

Hi, I created this clean replacement PR for #6890 from the latest main branch.

The previous PR included unrelated commits from #6841, so this PR contains only
the Python 3.14 event-handler annotation fix. I also adjusted the implementation
to avoid eager annotation work for unbound synthetic handlers after CodSpeed
reported a performance regression.

The Python 3.14 regression test and all 107 event unit tests pass, along with
Ruff formatting and lint checks.

[codspeed-hq]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 8 skipped benchmarks¹

---

_{Comparing harsh21234i:fix/6890-python314 (d3092cb) with main (092aa4f)}

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. ↩

[greptile-apps]

Greptile Summary

The PR caches successfully resolved state-handler annotations before runtime class patches and reuses them for event and upload validation. It also preserves retries for late-bound annotations and adds Python 3.14 regression coverage.

• Adds an annotation cache to EventHandler.
• Routes event and upload validation through the cached annotation helper.
• Adds regression tests and changelog fragments.

Confidence Score: 4/5

The PR should not merge until unresolved handler annotations are protected from being retried against an already patched state-class namespace.

The permanent-cache regression is fixed, but the previously reported uncached fallback remains: an initial NameError leaves no stable annotation snapshot, and event or upload validation can later resolve the annotation after runtime class attributes begin shadowing names on Python 3.14.

Files Needing Attention: packages/reflex-base/src/reflex_base/event/init.py

Important Files Changed

Filename	Overview
packages/reflex-base/src/reflex_base/event/init.py	Centralizes annotation resolution and caching, but the uncached unresolved-annotation fallback still permits a later retry after state-class namespace patching.
tests/units/test_event.py	Covers stable builtin resolution and successful late-bound retries, but not their combined sequence of initial failure followed by class patching.
news/6890.bugfix.md	Accurately describes the intended Python 3.14 annotation-shadowing fix.
packages/reflex-base/news/6890.bugfix.md	Adds the corresponding reflex-base bug-fix changelog fragment.

_{Reviews (4): Last reviewed commit: "Annotate deliberate unresolved type test" | Re-trigger Greptile}

[cubic-dev-ai]

All reported issues were addressed

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

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

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>