Preserve bound args for upload handlers

[puneetdixit200]

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Type of change

• Bug fix (non-breaking change which fixes an issue)

Changes To Core Features:

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Description

Fixes #5290.

EventHandler.__call__ returned immediately when it saw rx.upload_files(...) or rx.upload_files_chunk(...), so any other bound arguments supplied to the same event handler were dropped. This keeps the upload client-handler spec, but appends normal bound handler arguments to the resulting EventSpec so on_drop=State.handle_upload(rx.upload_files(...), field) preserves field.

AI-assisted: OpenAI Codex, with local review and verification.

Testing

• Red before fix: uv run pytest tests/units/components/core/test_upload.py::test_upload_files_preserves_bound_event_args -q failed because field was missing from the upload event args.
• uv run pytest tests/units/components/core/test_upload.py -q
• uv run pytest tests/units/test_event.py -q
• uv run pytest tests/units/test_app.py -q -k 'upload and not compile_writes_upload_files_provider_app_wrap'
• uv run ruff check packages/reflex-base/src/reflex_base/event/__init__.py tests/units/components/core/test_upload.py
• uv run pyright packages/reflex-base/src/reflex_base/event/__init__.py tests/units/components/core/test_upload.py (0 errors, 1 existing warning in event/__init__.py)
• git diff --check

Note: uv run pytest tests/units/test_app.py -q -k upload currently fails in unrelated test_compile_writes_upload_files_provider_app_wrap with AttributeError: 'DynamicState' object has no attribute 'dynamic'; the remaining 18 upload-selected app tests pass with that case excluded.

[greptile-apps]

Greptile Summary

This PR fixes issue #5290 by threading extra bound handler arguments through the full upload pipeline — from the Python EventHandler.__call__ compile step, through the JS client (uploadFiles / applyRestEvent), to the backend multipart parser and event dispatcher — for both buffered and streaming upload handlers.

• Python (event/__init__.py): EventHandler.__call__ no longer returns immediately on a FileUpload arg; it collects remaining bound args into the event spec payload and appends a __reflex_event_arg_names manifest so the JS client knows which keys to forward.
• JS (state.js, upload.js): applyRestEvent reads the manifest and passes the named args to uploadFiles, which serialises them as a __reflex_event_args JSON form field placed before file parts.
• Backend (_upload.py): _UploadChunkMultipartParser gains an on_args_ready callback deferring handler dispatch until the args field is parsed; _decode_event_args validates the field is a JSON object (400 for malformed or non-object input).

Confidence Score: 5/5

Safe to merge; the fix is complete across all three layers and is well-covered by both unit and integration tests.

The change is a targeted, well-tested fix with no regressions on existing upload paths. The two findings are minor edge cases that do not affect real-world usage.

The pyproject.toml dev version specifier should be updated to a stable release version before shipping.

Important Files Changed

Filename	Overview
packages/reflex-base/src/reflex_base/event/init.py	Core fix: EventHandler.call now detects FileUpload args, defers returning, appends extra payload args to the upload EventSpec, and adds a __reflex_event_arg_names manifest. UPLOAD_EVENT_ARG_NAMES_KEY itself is not added to the reserved-clash set.
packages/reflex-base/src/reflex_base/.templates/web/utils/state.js	applyRestEvent now reads the __reflex_event_arg_names manifest and passes the named args through to uploadFiles as extra_args.
packages/reflex-base/src/reflex_base/.templates/web/utils/helpers/upload.js	uploadFiles gains an extra_args parameter and appends it as a JSON __reflex_event_args form field before file parts.
packages/reflex-components-core/src/reflex_components_core/core/_upload.py	Backend: _UploadChunkMultipartParser gains on_args_ready callback; _decode_event_args validates JSON object; both buffered and streaming paths merge decoded args into the event payload.
tests/units/components/core/test_upload.py	Comprehensive unit tests cover compile-time EventSpec structure, JSON decoding edge cases, buffered form arg parsing, and streaming parser behavior.
tests/integration/test_upload.py	Integration tests extended to verify bound args reach both buffered and streaming handlers end-to-end.
packages/reflex-components-core/pyproject.toml	Minimum reflex-base dependency bumped to a pre-release dev specifier; should be updated to a stable version before release.

_{Reviews (4): Last reviewed commit: "Bump reflex-base min dep to dev version" | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 8 skipped benchmarks¹

---

_{Comparing puneetdixit200:fix/upload-bound-event-args (704f674) with main (9972800)}

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. ↩

[puneetdixit200]

The runtime upload path is covered on the current head now: the compiled event carries __reflex_event_arg_names, applyRestEvent forwards those keys to uploadFiles, uploadFiles sends them as Reflex-Event-Args, and the backend upload handlers merge that header into both buffered and chunk upload events.

Focused verification: uv run pytest tests/units/components/core/test_upload.py -k "upload_files_preserves_bound_event_args or upload_files_multiple_upload_args_raises or upload_files_bound_arg_reserved_name_raises" -q -> 3 passed, 12 deselected.

[FarhanAliRaza]

@greptile please rereview.

[FarhanAliRaza]

@greptile please rereview.