fix(tui): render full assistant text in scrollback (no history truncation)

ui-tui/src/__tests__/text.test.ts

@@ -1,7 +1,6 @@
 import { describe, expect, it } from 'vitest'
 
 import {
-  boundedHistoryRenderText,
   boundedLiveRenderText,
   buildToolTrailLine,
   edgePreview,
@@ -160,15 +159,6 @@ describe('boundedLiveRenderText', () => {
   })
 })
 
-describe('boundedHistoryRenderText', () => {
-  it('uses a non-live omission label for completed history', () => {
-    const out = boundedHistoryRenderText('abcdefghij', { maxChars: 4, maxLines: 10 })
-
-    expect(out).toContain('[showing tail; omitted')
-    expect(out).not.toContain('live tail')
-  })
-})
-
 describe('edgePreview', () => {
   it('keeps both ends for long text', () => {
     expect(edgePreview('Vampire Bondage ropes slipped from her neck, still stained with blood', 8, 18)).toBe(

ui-tui/src/__tests__/virtualHeights.test.ts

@@ -39,4 +39,19 @@ describe('virtual height estimates', () => {
 
     expect(withSep).toBe(base + 2)
   })
+
+  it('caps wrapped-line counting so giant assistant turns do not block offset rebuilds', () => {
+    // wrappedLines is invoked once per uncached message during
+    // useVirtualHistory's offset rebuild. Unbounded counting on a long
+    // assistant response (10k+ chars × every row × every rebuild) blocks
+    // the UI on cold mount. Cap is ~800 rows; post-mount Yoga
+    // measurement converges to the true height regardless.
+    const giant = 'x'.repeat(1_000_000)
+    const t0 = performance.now()
+    const rows = wrappedLines(giant, 80)
+    const elapsed = performance.now() - t0
+
+    expect(rows).toBeLessThanOrEqual(800)
+    expect(elapsed).toBeLessThan(50)
+  })
 })

ui-tui/src/app/useMainApp.ts

@@ -3,7 +3,7 @@ import { useStore } from '@nanostores/react'
 import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
 
 import { STARTUP_RESUME_ID } from '../config/env.js'
-import { FULL_RENDER_TAIL_ITEMS, MAX_HISTORY, WHEEL_SCROLL_STEP } from '../config/limits.js'
+import { MAX_HISTORY, WHEEL_SCROLL_STEP } from '../config/limits.js'
 import { SECTION_NAMES, sectionMode } from '../domain/details.js'
 import { attachedImageNotice, imageTokenMeta } from '../domain/messages.js'
 import { fmtCwdBranch, shortCwd } from '../domain/paths.js'
@@ -274,7 +274,6 @@ export function useMainApp(gw: GatewayClient) {
       estimatedMsgHeight(virtualRows[index]!.msg, cols, {
         compact: ui.compact,
         details: detailsVisible,
-        limitHistory: index < virtualRows.length - FULL_RENDER_TAIL_ITEMS,
         userPrompt: ui.theme.brand.prompt,
         withSeparator: virtualRows[index]!.msg.role === 'user' && firstUserIdx >= 0 && index > firstUserIdx
       }),

ui-tui/src/components/appLayout.tsx

@@ -7,7 +7,6 @@ import type { AppLayoutProps } from '../app/interfaces.js'
 import { $isBlocked, $overlayState, patchOverlayState } from '../app/overlayStore.js'
 import { $uiState } from '../app/uiStore.js'
 import { INLINE_MODE, SHOW_FPS } from '../config/env.js'
-import { FULL_RENDER_TAIL_ITEMS } from '../config/limits.js'
 import { PLACEHOLDER } from '../content/placeholders.js'
 import {
   COMPOSER_PROMPT_GAP_WIDTH,
@@ -125,7 +124,6 @@ const TranscriptPane = memo(function TranscriptPane({
                   compact={ui.compact}
                   detailsMode={ui.detailsMode}
                   detailsModeCommandOverride={ui.detailsModeCommandOverride}
-                  limitHistoryRender={row.index < transcript.historyItems.length - FULL_RENDER_TAIL_ITEMS}
                   msg={row.msg}
                   sections={ui.sections}
                   t={ui.theme}

ui-tui/src/components/messageLine.tsx

@@ -7,7 +7,6 @@ import { userDisplay } from '../domain/messages.js'
 import { ROLE } from '../domain/roles.js'
 import { transcriptBodyWidth, transcriptGutterWidth } from '../lib/inputMetrics.js'
 import {
-  boundedHistoryRenderText,
   boundedLiveRenderText,
   compactPreview,
   hasAnsi,
@@ -32,7 +31,6 @@ export const MessageLine = memo(function MessageLine({
   detailsMode = 'collapsed',
   detailsModeCommandOverride = false,
   isStreaming = false,
-  limitHistoryRender = false,
   msg,
   sections,
   t,
@@ -149,7 +147,7 @@ export const MessageLine = memo(function MessageLine({
         // streamingMarkdown.tsx for the cost model.
         <StreamingMd cols={bodyWidth} compact={compact} t={t} text={boundedLiveRenderText(msg.text)} />
       ) : (
-        <Md cols={bodyWidth} compact={compact} t={t} text={limitHistoryRender ? boundedHistoryRenderText(msg.text) : msg.text} />
+        <Md cols={bodyWidth} compact={compact} t={t} text={msg.text} />
       )
     }
 
@@ -215,7 +213,6 @@ interface MessageLineProps {
   detailsMode?: DetailsMode
   detailsModeCommandOverride?: boolean
   isStreaming?: boolean
-  limitHistoryRender?: boolean
   msg: Msg
   sections?: SectionVisibility
   t: Theme

ui-tui/src/config/limits.ts

@@ -3,15 +3,6 @@ export const LARGE_PASTE = { chars: 8000, lines: 80 }
 export const LIVE_RENDER_MAX_CHARS = 16_000
 export const LIVE_RENDER_MAX_LINES = 240
 
-// History-render bounds for messages outside FULL_RENDER_TAIL. Each rendered
-// line ≈ 1 Yoga/Text node + inline spans, so this is the dominant lever on
-// cold-mount cost during PageUp catch-up. 16 lines × 25 mounted ≈ 400 nodes
-// — comfortably inside the 16ms per-frame budget. User pages back to
-// recognize, not to read; full re-render once it falls inside the tail.
-export const HISTORY_RENDER_MAX_CHARS = 800
-export const HISTORY_RENDER_MAX_LINES = 16
-export const FULL_RENDER_TAIL_ITEMS = 8
-
 export const LONG_MSG = 300
 export const MAX_HISTORY = 800
 export const THINKING_COT_MAX = 160

ui-tui/src/lib/text.ts

@@ -1,6 +1,4 @@
 import {
-  HISTORY_RENDER_MAX_CHARS,
-  HISTORY_RENDER_MAX_LINES,
   LIVE_RENDER_MAX_CHARS,
   LIVE_RENDER_MAX_LINES,
   THINKING_COT_MAX
@@ -129,11 +127,6 @@ export const boundedLiveRenderText = (
   { maxChars = LIVE_RENDER_MAX_CHARS, maxLines = LIVE_RENDER_MAX_LINES } = {}
 ) => boundedRenderText(text, 'showing live tail', { maxChars, maxLines })
 
-export const boundedHistoryRenderText = (
-  text: string,
-  { maxChars = HISTORY_RENDER_MAX_CHARS, maxLines = HISTORY_RENDER_MAX_LINES } = {}
-) => boundedRenderText(text, 'showing tail', { maxChars, maxLines })
-
 const boundedRenderText = (
   text: string,
   labelPrefix: string,

ui-tui/src/lib/virtualHeights.ts

@@ -1,7 +1,6 @@
 import type { Msg } from '../types.js'
 
 import { transcriptBodyWidth } from './inputMetrics.js'
-import { boundedHistoryRenderText } from './text.js'
 
 const hashText = (text: string) => {
   let h = 5381
@@ -30,10 +29,40 @@ export const messageHeightKey = (msg: Msg) => {
   ].join(':')
 }
 
-export const wrappedLines = (text: string, width: number) => {
+// Hard cap on rows the estimator will count. Each row above this is
+// invisible to the estimator (gets clipped to MAX_ESTIMATE_LINES), but
+// post-mount Yoga measurement converges to the real height on first
+// render. Without this, a long assistant turn (10k+ chars) costs O(text)
+// per offset rebuild × every uncached item — cold-mounting a 1000-row
+// transcript becomes a multi-million-char wrap walk that blocks the UI.
+//
+// 800 covers any realistic assistant message (the prior history-clip
+// ceiling was 16 lines, then full text — this is the sane middle).
+const MAX_ESTIMATE_LINES = 800
+
+export const wrappedLines = (text: string, width: number, maxLines: number = MAX_ESTIMATE_LINES) => {
   const w = Math.max(1, width)
+  // Worst case: every cell is its own row at width=1, plus a small
+  // slack for the trailing partial line. Walking past this byte budget
+  // cannot increase n any further once n is already past maxLines, so
+  // bail. Saves O(text) walks on multi-megabyte single-line messages.
+  const budget = Math.min(text.length, maxLines * w + maxLines)
+  let n = 0
+  let start = 0
+
+  for (let i = 0; i <= budget; i++) {
+    if (i === text.length || i === budget || text.charCodeAt(i) === 10) {
+      const rows = Math.max(1, Math.ceil((i - start) / w))
+      n += rows >= maxLines - n ? maxLines - n : rows
+      start = i + 1
+
+      if (n >= maxLines) {
+        return maxLines
+      }
+    }
+  }
 
-  return text.split('\n').reduce((n, line) => n + Math.max(1, Math.ceil(line.length / w)), 0)
+  return n
 }
 
 export const estimatedMsgHeight = (
@@ -42,13 +71,11 @@ export const estimatedMsgHeight = (
   {
     compact,
     details,
-    limitHistory = false,
     userPrompt = '',
     withSeparator = false
   }: {
     compact: boolean
     details: boolean
-    limitHistory?: boolean
     userPrompt?: string
     withSeparator?: boolean
   }
@@ -70,11 +97,16 @@ export const estimatedMsgHeight = (
   }
 
   const bodyWidth = transcriptBodyWidth(cols, msg.role, userPrompt)
-  const text = msg.role === 'assistant' && limitHistory ? boundedHistoryRenderText(msg.text) : msg.text
+  const text = msg.text
   let h = wrappedLines(text || ' ', bodyWidth)
 
   if (!compact && msg.role === 'assistant') {
-    h += Math.min(6, (text.match(/\n\s*\n/g) ?? []).length)
+    // Paragraph gaps add up to 6 extra rows of breathing room. Slice
+    // first so the regex never walks more than the first ~16k chars of
+    // a giant assistant message — post-mount Yoga measurement converges
+    // to the real height regardless of how the estimate undercounts.
+    const scan = text.length > 16_000 ? text.slice(0, 16_000) : text
+    h += Math.min(6, (scan.match(/\n\s*\n/g) ?? []).length)
   }
 
   if (details) {