fix(app): reuse terminal cells during serialization (#46763)

Author: Hona

packages/app/e2e/performance/terminals/README.md

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+# Native Terminal Benchmark
+
+Manual Windows benchmark. Run only in an isolated development worktree. It does
+not connect to an OpenCode service, user profile, or database.
+
+Build from `packages/app` with
+`bun x vite build --config e2e/performance/terminals/vite.config.ts`, then freeze
+`dist` outside the repository. Set `PLAYWRIGHT_BUILD=1`, `PLAYWRIGHT_BASE_URL` to
+an unused loopback URL, `TERMINAL_BUILD` to the frozen build,
+`TERMINAL_ARTIFACTS` to an existing external directory, and `TERMINAL_RESULTS`
+to an external result directory. Run:
+
+```sh
+bun x playwright test --config e2e/performance/terminals/playwright.config.ts --repeat-each=20
+```
+
+The runner owns its preview server and each test owns a PowerShell ConPTY process.
+Session metadata is deterministic. Native output is forwarded through Playwright's
+WebSocket fixture into the real production `Terminal`, writer, Ghostty WASM/canvas,
+and serializer. No output is dropped, paused, or delayed. This is native terminal
+plus production renderer evidence, not the production PTY backend or Electron IPC.
+
+The workload is 12,000 colored build/test log lines with file paths, durations, and
+result descriptions. Cases separate visible output, the same output while hidden,
+and closing the session tab after filling the configured scrollback. Ghostty
+converts the app's 10,000-line setting to bytes at its initial 80-column width;
+resizing reduces the effective row capacity. The report records actual retained
+rows and the first retained fixture record rather than assuming 10,000 rows. Completion
+requires the final marker in Ghostty and completion of its write callbacks, not
+just WebSocket delivery. Teardown requires Home readiness and the final serialized
+snapshot. Input, focus, resizing, and native process survival are checked.
+
+`probe.ts` is included only by this benchmark build. It observes actual writes,
+renderer calls, and serialization. Chrome `TaskDuration` measures renderer task
+time, not total process CPU or RAM. For attribution, set
+`OPENCODE_PERFORMANCE_TRACE_DIR`; keep traced runs separate from clean timing.
+`TERMINAL_DRAW_PROBE=1` separately counts actual canvas draws to verify hidden
+rendering; do not mix these instrumented samples with clean timing.
+Use `TERMINAL_REVISION` and `TERMINAL_BUNDLE` to identify frozen artifacts.
+`TERMINAL_SCREENSHOTS` captures the visible result after timing.
+
+The benchmark has no machine-dependent performance thresholds. Keep raw logs,
+snapshots, traces, and screenshots outside Git. Run heavy work through the
+coordinator's exclusive gate when participating in a shared performance wave.

packages/app/e2e/performance/terminals/playwright.config.ts

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+import { defineConfig } from "@playwright/test"
+import config from "../../../playwright.config"
+
+export default defineConfig({
+  ...config,
+  testDir: ".",
+  testIgnore: [],
+  testMatch: "terminal-benchmark.spec.ts",
+  workers: 1,
+  retries: 0,
+  timeout: 120_000,
+  outputDir: process.env.TERMINAL_RESULTS,
+  reporter: [["line"]],
+  webServer: {
+    command: `bun x vite preview --host 127.0.0.1 --port ${new URL(process.env.PLAYWRIGHT_BASE_URL!).port} --strictPort --outDir ${process.env.TERMINAL_BUILD}`,
+    url: process.env.PLAYWRIGHT_BASE_URL,
+    reuseExistingServer: false,
+  },
+  use: { ...config.use, viewport: { width: 1440, height: 900 }, trace: "off", video: "off", serviceWorkers: "block" },
+})

packages/app/e2e/performance/terminals/probe.ts

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+import { Terminal } from "ghostty-web"
+import { SerializeAddon } from "../../../src/session/terminal/serialize"
+
+export type TerminalProbe = {
+  term?: Terminal
+  writes: number
+  pending: number
+  bytes: number
+  renders: number
+  hiddenRenders: number
+  draws: number
+  hiddenDraws: number
+  serialized: { ms: number; bytes: number; value: string }[]
+}
+
+declare global {
+  interface Window {
+    terminalProbe: TerminalProbe
+  }
+}
+
+const probe: TerminalProbe = {
+  writes: 0,
+  pending: 0,
+  bytes: 0,
+  renders: 0,
+  hiddenRenders: 0,
+  draws: 0,
+  hiddenDraws: 0,
+  serialized: [],
+}
+window.terminalProbe = probe
+const open = Terminal.prototype.open
+Terminal.prototype.open = function (element) {
+  probe.term = this
+  open.call(this, element)
+  // Ghostty does not expose render events. This benchmark-only wrapper observes its
+  // actual renderer; it does not alter scheduling, parsing, or drawing.
+  const renderer = (this as unknown as { renderer: { render: (...args: unknown[]) => void } }).renderer
+  const render = renderer.render
+  let hidden = false
+  renderer.render = function (...args) {
+    probe.renders++
+    hidden = !element.checkVisibility()
+    if (hidden) probe.hiddenRenders++
+    return render.apply(this, args)
+  }
+  if (new URL(location.href).searchParams.has("terminalDrawProbe")) {
+    const context = element.querySelector("canvas")!.getContext("2d")!
+    const draw = context.drawImage
+    context.drawImage = function (...args: unknown[]) {
+      probe.draws++
+      if (hidden) probe.hiddenDraws++
+      Reflect.apply(draw, this, args)
+    }
+  }
+}
+const write = Terminal.prototype.write
+Terminal.prototype.write = function (data, done) {
+  probe.writes++
+  probe.pending++
+  probe.bytes += typeof data === "string" ? new TextEncoder().encode(data).byteLength : data.byteLength
+  return write.call(this, data, () => {
+    probe.pending--
+    done?.()
+  })
+}
+const serialize = SerializeAddon.prototype.serialize
+SerializeAddon.prototype.serialize = function (options) {
+  const start = performance.now()
+  const value = serialize.call(this, options)
+  probe.serialized.push({ ms: performance.now() - start, bytes: new TextEncoder().encode(value).byteLength, value })
+  return value
+}

packages/app/e2e/performance/terminals/shell.ps1

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+param([Parameter(Mandatory = $true)][string]$Fixture)
+$ErrorActionPreference = 'Stop'
+[Console]::WriteLine('TERMINAL_FIXTURE_READY')
+while ($null -ne ($command = [Console]::ReadLine())) {
+  if ($command -eq 'exit') { exit 0 }
+  if ($command -eq 'run') {
+    foreach ($line in [System.IO.File]::ReadLines($Fixture)) {
+      [Console]::WriteLine($line)
+    }
+    [Console]::WriteLine('TERMINAL_WORKLOAD_DONE')
+  }
+  if ($command -eq 'ping') { [Console]::WriteLine('TERMINAL_PROCESS_ALIVE') }
+}