Make reflex init and docs uv-first

[GautamBytes]

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Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

New Feature Submission:

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Changes To Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?

Description

• make fresh reflex init projects generate pyproject.toml by default
• keep existing requirements.txt projects working without creating a second manifest
• update README, getting started docs, and onboarding docs to use uv
• improve pyproject.toml dependency detection so only real Reflex dependencies count

After these steps, you're ready to open a pull request.

closes #6269

[greptile-apps]

Greptile Summary

This PR makes reflex init uv-first by defaulting to pyproject.toml generation for new apps, while preserving backward compatibility for existing projects using requirements.txt. It also updates the README, getting-started, and onboarding docs to use uv commands throughout.

Key changes:

• initialize_python_manifest in frontend_skeleton.py contains the core logic: new apps get pyproject.toml, existing requirements.txt projects are left untouched, and existing pyproject.toml files are preserved but checked for a Reflex dependency
• pyproject_toml_template in compiler/templates.py generates a minimal PEP 517-compatible pyproject.toml
• The _init entry point in reflex.py now surfaces appropriate uv sync / uv pip install next-steps after initialization
• Six unit tests cover all manifest-detection branches including Poetry-style dependencies
• Integration test now verifies pyproject.toml is created and requirements.txt is absent for blank template init

Minor issues: the Windows uv installation command is absent from the README, and a RequirementsTxt-namespaced constant is used in a pyproject.toml-specific user-facing message.

Confidence Score: 4/5

Safe to merge — core logic is correct and well-tested, backward compatibility with requirements.txt is preserved.

No P0 or P1 findings. Three P2 issues remain: missing Windows install guidance in README, a RequirementsTxt constant used in a pyproject.toml message, and a minor regex delimiter issue in the fallback TOML parser. None of these block merge but the README gap is worth addressing before release.

README.md (missing Windows uv install guidance), reflex/reflex.py (RequirementsTxt constant in pyproject message), reflex/utils/frontend_skeleton.py (fallback regex)

Important Files Changed

Filename	Overview
reflex/utils/frontend_skeleton.py	Adds initialize_python_manifest and helpers for pyproject.toml/requirements.txt detection — logic is correct and well-tested; fallback TOML regex has a minor delimiter-matching gap
reflex/reflex.py	Calls initialize_python_manifest post-init and shows uv next-steps; pyproject.toml message incorrectly references RequirementsTxt.DEFAULTS_STUB
packages/reflex-base/src/reflex_base/compiler/templates.py	Adds pyproject_toml_template that generates a minimal, valid pyproject.toml with pinned reflex version
packages/reflex-base/src/reflex_base/constants/config.py	Adds DEFAULT_VERSION and REQUIRES_PYTHON constants to PyprojectToml namespace — clean addition
README.md	Switches to uv-first getting-started flow; Windows uv installation guidance is missing
tests/units/utils/test_utils.py	Comprehensive unit tests for all manifest initialization branches including Poetry-style, fallback, existing files — good edge-case coverage
tests/integration/init-test/in_docker_test_script.sh	Installs uv in Docker and asserts pyproject.toml created / requirements.txt absent after blank init
reflex/utils/templates.py	Remote template install hint updated to prefer uv sync for pyproject.toml and uv pip install for requirements.txt templates

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[reflex init] --> B{rxconfig.py exists?}
    B -- Yes --> C[reinit: skip app creation]
    B -- No --> D[initialize_default_app / remote template]
    D --> E[initialize_python_manifest]
    C --> E
    E --> F{pyproject.toml exists?}
    F -- Yes --> G{has reflex dependency?}
    G -- Yes --> H[return kind=pyproject]
    G -- No --> I[return kind=pyproject\nneeds_manual=True]
    F -- No --> J{requirements.txt exists?}
    J -- Yes --> K[_initialize_requirements_txt\nreturn kind=requirements]
    J -- No --> L[_initialize_pyproject_toml\ncreate new file\nreturn kind=pyproject]
    H --> M{manifest.kind?}
    I --> M
    K --> M
    L --> M
    M -- pyproject --> N[Show: uv sync + uv run reflex run]
    M -- requirements --> O[Show: uv pip install -r requirements.txt]

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