Sticky prompt:
The loop was skipping `first` (the first row in the viewport) when
looking for a user message scrolled above the top edge. If `first`
itself was a user row that had just ticked above the viewport, we'd
fall through the early-return guard (`role === 'user' && !above`),
then walk from `first - 1` backward — never rechecking `first`, never
finding anything, returning '' and leaving the sticky empty. This is
why it felt "stuck" at the start: one-turn sessions with the user row
exactly at/near the top never surfaced the breadcrumb.
Collapsed the two branches into one loop starting at `first`: nearest
user wins — still-on-screen → empty (redundant to echo), already
above → text. Same semantics, covers the gap.
Scrollbar:
`useSyncExternalStore` snapshot was `scrollTop:vp:scrollHeight` —
scrollHeight ticks up by ~1 row on every streamed chunk, forcing a
re-render per chunk. Quantized snapshot to the displayed values
(`thumbTop:thumbSize:vp`) so we only re-render when the bar actually
changes. Drops render count per turn by ~100x during streaming and
stops the "constantly resizes" flicker.
Hoist turn state from a 286-line hook into $turnState atom + turnController
singleton. createGatewayEventHandler becomes a typed dispatch over the
controller; its ctx shrinks from 30 fields to 5. Event-handler refs and 16
threaded actions are gone.
Fold three createSlash*Handler factories into a data-driven SlashCommand[]
registry under slash/commands/{core,session,ops}.ts. Aliases are data;
findSlashCommand does name+alias lookup. Shared guarded/guardedErr combinator
in slash/guarded.ts.
Split constants.ts + app/helpers.ts into config/ (timing/limits/env),
content/ (faces/placeholders/hotkeys/verbs/charms/fortunes), domain/ (roles/
details/messages/paths/slash/viewport/usage), protocol/ (interpolation/paste).
Type every RPC response in gatewayTypes.ts (26 new interfaces); drop all
`(r: any)` across slash + main app.
Shrink useMainApp from 1216 -> 646 lines by extracting useSessionLifecycle,
useSubmission, useConfigSync. Add <Fg> themed primitive and strip ~50
`as any` color casts.
Tests: 50 passing. Build + type-check clean.
