Add IME underline, I-beam cursor, and horizontal scroll to Input

docs/PLAN.md

@@ -221,7 +221,7 @@ Deferred until a real need: Markdown/TextView, Dock, VirtualList, window-wide te
 
 Our divergence from gpui-kit held: the per-size metrics resolve from **the theme's size table at paint time**, not from constants in the component layer. All ten controls implement `Sizable`; `Size::Custom(side)` derives the other metrics from the side length. Still open, when a real need arrives: TOML overrides for the size table in `ThemeDefinition`, and per-platform size tables from the Phase F native-metrics work.
 
-### 6.2 Input completion (unit 10 finishing pass) — in progress (steps 1–5 landed 2026-10-29)
+### 6.2 Input completion (unit 10 finishing pass) — ✅ landed (2026-10-29)
 
 Gap analysis against gpuikit's input (2026-10-29; source read as an API reference, §9 — no porting). gpuikit splits input three ways: core state whose edits are actions, infrastructure (`bindings` / `blink` / `bidi`), and a chrome-less element with chrome in wrapper elements. We keep one component with chrome included; only the ideas below are adopted.
 
@@ -236,7 +236,7 @@ Remaining, in order:
 | 3 | Read-only, Escape-blur, triple-click | ✅ Landed. Read-only: focus, movement, selection, copy still work; edits, paste, cut (clipboard included), undo/redo and IME refused — distinct from disabled; programmatic setters unaffected; the caret is hidden while read-only (a caret promises typing lands there). Escape → `window.blur()`. Triple-click selects all (single-line) |
 | 4 | Actions + key context | ✅ Landed. 25 `actions!(input, …)` + an `"Input"` key context; the element registers `on_action` handlers and the residual `on_key_down` only inserts printable typed chars. `InputBindings` table of `Option<KeyBinding>` fields — `Default` is platform defaults (cmd/alt on macOS, ctrl elsewhere), `empty()` starts bare, any field replaceable/unbindable; `bind_input_keys(cx, None | table)` registers at startup (gallery + tests call it). Verified gpui semantics first: matched bindings consume the keystroke before `on_key_down`, and actions claim by default in bubble (`cx.propagate()` yields — Copy does when the selection is empty). macOS jump extras (`cmd-left/right/up/down`, `cmd-shift-left/right`) are appended in `into_bindings`, not field-configurable |
 | 5 | Caret blink | ✅ Landed. A private `CaretBlink` entity per `InputState`: 500 ms tick on the GPUI executor, visible on focus and hidden after one interval. Any field change (`InputState::notify`) pauses it — caret solid, cycle restarts — so typing, moving and dragging never hide it; generation counters invalidate stale ticks. Read-only suppresses the caret entirely. `caret_visible(focused, cx)` is the single gate used by paint and tests |
-| 6 | Paint polish | IME marked-text underline; I-beam cursor on hover; two-sided horizontal scroll (clamped offset in state, follows caret) plus horizontal wheel scroll |
+| 6 | Paint polish | ✅ Landed. IME composition underline (1 px, foreground token) under the marked range. I-beam hover cursor via a canvas-prepaint hitbox + `set_cursor_style` in paint. Two-sided horizontal scroll: `scroll_offset` lives in state; caret-affecting changes set a pending flag that the next paint consumes with a fresh layout (two-sided pull-back + clamp to content), while `scroll_by` (wheel, `ScrollEvent`, lines→pixels via a fixed unit) bypasses the flag so manual pans survive. Scroll-aware hit-testing, IME `bounds_for_range` and drag select all come free through the scroll-adjusted origin |
 
 Deferred until a real need: bidi/RTL; prefix/suffix adornments and a form field wrapper (label/description/error — separate units); `SubmitOn` enter/cmd-enter modes (multiline concern); `Undo`/`Redo` events; selection/cursor color overrides (theme tokens are deliberate); password masking, max length, clear button (gpuikit has none of these either — decide on first need).