ENG-9860 fix(vars): preserve custom Field attributes in state metaclass

[FarhanAliRaza]

BaseStateMeta rebuilt Field instances for state annotations, discarding any custom attributes callers had set. Copy over attrs the rebuilt field did not recompute via Field._copy_custom_attrs_from so subclassed or customized fields keep their extra state.

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

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[greptile-apps]

Greptile Summary

This PR fixes BaseStateMeta silently discarding custom attributes set on Field instances when it rebuilds them during state class construction. The fix adds a source_field parameter to Field.__init__ that deep-copies any non-reserved attributes from the original field after the rebuilt field has been fully initialized.

• base.py: Adds _RESERVED_FIELD_ATTRS = frozenset({\"annotation\"}) and a source_field parameter; the copy loop runs after all standard init processing so it cannot overwrite default, default_factory, type attrs, or is_var. Three BaseStateMeta rebuild sites now pass source_field=value.
• test_base.py: Five new tests cover annotated rebuild, type-inferred rebuild, factory rebuild, annotation exclusion, and deep-copy isolation of mutable attributes.

Confidence Score: 5/5

Safe to merge — the change is additive, well-contained, and backed by targeted tests.

The copy loop runs strictly after all standard Field.init processing so it cannot overwrite computed type or default attrs. The annotation guard correctly prevents the one known duck-typing hazard. copy.deepcopy per-attribute handles the mutable aliasing edge case. All three rebuild sites in BaseStateMeta were updated consistently, and five tests cover the key scenarios.

No files require special attention.

Important Files Changed

Filename	Overview
packages/reflex-base/src/reflex_base/vars/base.py	Adds source_field parameter to Field.__init__ that deep-copies non-reserved custom attributes after full init; _RESERVED_FIELD_ATTRS correctly guards annotation so pydantic duck-typing via get_field_type is not broken.
tests/units/reflex_base/vars/test_base.py	New test suite covering annotated rebuild, unannotated type-inferred rebuild, unannotated factory rebuild, annotation exclusion guard, and mutable deep-copy isolation.
packages/reflex-base/news/6726.bugfix.md	Changelog entry correctly describes the fix.
tests/units/reflex_base/vars/init.py	Empty __init__.py added to make the new test directory a package.

_{Reviews (2): Last reviewed commit: "fix(vars): deep-copy custom Field attrs ..." | 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-9860-state-metaclass-should-preserve-custom-attributes-on-field (c577490) 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. ↩

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[masenf]

i think this copying functionality should be part of __init__; you can add another optional param source_field and apply the copying of extra values from there.

what greptile says about deepcopying the values makes sense to me, we don't want to have shared references to mutable types across different Field instances.

having a list of reserved attributes also makes sense to avoid misidentification with pydantic fields.

add changelog entry