ENG-9859 fix(state): preserve source function __dict__ and kwdefaults in _copy…

[FarhanAliRaza]

…_fn (ENG-9859)

When the State metaclass pulls a computed-var getter or event handler in from a mixin, _copy_fn rebuilds the function via FunctionType, which drops the function's dict. Previously it hand-copied only the background-task and event-actions markers back on, silently losing any other attribute a framework or downstream user set on the getter/handler.

Copy the full dict onto the copy, which subsumes the per-marker copies and lets arbitrary markers (e.g. Reflex Enterprise's _auth tag) survive mixin inheritance. Also carry kwdefaults, which FunctionType likewise drops — without it a mixin handler with a keyword-only default raised TypeError when called through the subclass.

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Type of change

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• New feature (non-breaking change which adds functionality)

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[greptile-apps]

Greptile Summary

This PR fixes _copy_fn in BaseState so that functions copied from mixins retain their full __dict__ and __kwdefaults__, rather than only the handful of attributes that were previously hard-coded.

• Replaces three separate setattr/object.__setattr__ calls with a single newfn.__dict__.update(fn.__dict__), which subsumes all prior per-marker copies and future-proofs arbitrary user-set attributes.
• Adds newfn.__kwdefaults__ = fn.__kwdefaults__ to fix a TypeError that previously occurred when a mixin event handler declared keyword-only arguments with defaults.
• Three new targeted tests verify __dict__ independence, __kwdefaults__ round-trip invocability, and the preserved background-task marker.

Confidence Score: 5/5

Safe to merge — the change is a narrow, well-tested fix to function copying in mixin inheritance with no impact on the broader state machinery.

The fix replaces explicit per-attribute copies with a clean __dict__.update plus __kwdefaults__ assignment. Both operations on a plain FunctionType are straightforward and carry no hidden side effects. The previous object.__setattr__ path for EVENT_ACTIONS_MARKER is fully subsumed by the new approach since function attributes live in __dict__. Three new tests directly exercise the changed code paths, including an end-to-end callable invocation of a handler with keyword-only defaults.

No files require special attention.

Important Files Changed

Filename	Overview
reflex/state.py	Replaces hand-copied attribute assignments in _copy_fn with __dict__.update + __kwdefaults__ copy, fixing mixin inheritance for arbitrary function attributes and keyword-only defaults.
tests/units/test_state.py	Adds three new test cases covering: custom __dict__ attribute preservation, __kwdefaults__ preservation with a callable invocation check, and background-task marker preservation via mixin inheritance.
news/6725.bugfix.md	New changelog entry describing the bugfix for mixin function attribute and kwdefault preservation.

_{Reviews (2): Last reviewed commit: "chore: shorten changelog entry" | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 8 skipped benchmarks¹

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_{Comparing FarhanAliRaza:farhan/eng-9859-basestate_copy_fn-should-preserve-the-source-functions (6fc747c) with main (948c619)²}

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. ↩

2. No successful run was found on main (3b97060) during the generation of this report, so 948c619 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[masenf]

looks good, needs a changelog entry