fix: chat input crashing when moving the cursor (#33)

Reviewed-on: #33

crates/ui/src/input/display_map/mod.rs

@@ -0,0 +1,69 @@
+/// Display mapping system for Editor/Input.
+///
+/// This module implements a layered display mapping architecture:
+/// - **WrapMap**: Handles soft-wrapping (buffer → wrap rows)
+/// - **FoldMap**: Handles folding (wrap rows → display rows)
+/// - **DisplayMap**: Public facade for Editor/Input
+///
+/// The goal is to provide a clean, unified API where Editor only needs to know
+/// about `BufferPoint ↔ DisplayPoint` mapping, without worrying about internal wrap/fold complexity.
+mod display_map;
+mod fold_map;
+#[cfg(not(target_family = "wasm"))]
+mod folding;
+#[cfg(target_family = "wasm")]
+pub mod folding;
+mod text_wrapper;
+mod wrap_map;
+
+// Re-export public API
+// Re-export FoldRange and extract_fold_ranges
+pub use folding::FoldRange;
+
+pub use self::display_map::DisplayMap;
+pub(crate) use self::text_wrapper::LineLayout;
+
+/// Position in the buffer (logical text).
+///
+/// - `line`: 0-based logical line number (split by `\n`)
+/// - `col`: 0-based column offset (byte offset)
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct BufferPoint {
+    pub line: usize,
+    pub col: usize,
+}
+
+impl BufferPoint {
+    pub fn new(line: usize, col: usize) -> Self {
+        Self { line, col }
+    }
+}
+
+/// Position after soft-wrapping but before folding (internal).
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub(super) struct WrapPoint {
+    pub row: usize,
+    pub col: usize,
+}
+
+impl WrapPoint {
+    pub fn new(row: usize, col: usize) -> Self {
+        Self { row, col }
+    }
+}
+
+/// Final display position (after soft-wrapping and folding).
+///
+/// - `row`: 0-based display row (final visible row)
+/// - `col`: 0-based display column
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct DisplayPoint {
+    pub row: usize,
+    pub col: usize,
+}
+
+impl DisplayPoint {
+    pub fn new(row: usize, col: usize) -> Self {
+        Self { row, col }
+    }
+}