**[REQUIRED]** Use for ALL Streamlit tasks: creating, editing, debugging, beautifying, styling, theming, optimizing, or deploying Streamlit applications. Also required for building custom components (inline or packaged), using st.components.v2, or any HTML/JS/CSS component work. Triggers: streamlit, st., dashboard, app.py, beautify, style, CSS, color, background, theme, button, widget styling, custom component, st.components, packaged component, pyproject.toml, asset_dir, CCv2, HTML/JS component.
Builds bidirectional Streamlit Custom Components v2 (CCv2) using `st.components.v2.component`. Use when authoring inline HTML/CSS/JS components or packaged components (manifest `asset_dir`, js/css globs), wiring state/trigger callbacks, theming via `--st-*` CSS variables, or bundling with Vite / `component-template` v2.
Building dashboards in Streamlit. Use when creating KPI displays, metric cards, or data-heavy layouts. Covers borders, cards, responsive layouts, and dashboard composition.
Optimizing Streamlit app performance. Use when apps are slow, rerunning too often, or loading heavy content. Covers caching, fragments, and static vs dynamic widget choices.