fix(cli): -c picks the most recently used session

ui-tui/src/lib/perfPane.tsx

@@ -0,0 +1,82 @@
+// Perf instrumentation: wraps React.Profiler around named panes and writes
+// commit timings to a log file when HERMES_DEV_PERF is set. Enabled per-run
+// via the env var; zero-cost (Profiler is replaced by a Fragment) when off.
+//
+// Log format: one JSON object per line, for easy `jq` filtering. We only
+// log commits that exceed a threshold (default 2ms) so the file doesn't
+// fill up with sub-millisecond idle renders. Tune via HERMES_DEV_PERF_MS.
+//
+// Usage in consumers:
+//   import { PerfPane } from './perfPane.js'
+//   <PerfPane id="transcript"> ... </PerfPane>
+//
+// Inspect with:
+//   tail -f ~/.hermes/perf.log | jq -c 'select(.actualMs > 8)'
+//   jq -s 'group_by(.id) | map({id: .[0].id, count: length, p50: (sort_by(.actualMs) | .[length/2|floor].actualMs), p99: (sort_by(.actualMs) | .[length*0.99|floor].actualMs)})' ~/.hermes/perf.log
+
+import { appendFileSync, mkdirSync } from 'node:fs'
+import { homedir } from 'node:os'
+import { dirname, join } from 'node:path'
+
+import { Profiler, type ProfilerOnRenderCallback, type ReactNode } from 'react'
+
+const ENABLED = /^(?:1|true|yes|on)$/i.test((process.env.HERMES_DEV_PERF ?? '').trim())
+const THRESHOLD_MS = Number(process.env.HERMES_DEV_PERF_MS ?? '2') || 2
+const LOG_PATH = process.env.HERMES_DEV_PERF_LOG?.trim() || join(homedir(), '.hermes', 'perf.log')
+
+let initialized = false
+
+const ensureLogDir = () => {
+  if (initialized) {
+    return
+  }
+
+  initialized = true
+
+  try {
+    mkdirSync(dirname(LOG_PATH), { recursive: true })
+  } catch {
+    // Best-effort — if we can't create the dir (readonly fs, /tmp, etc.)
+    // the appendFileSync calls below will throw silently and we drop the
+    // sample. Perf logging should never crash the TUI.
+  }
+}
+
+const onRender: ProfilerOnRenderCallback = (id, phase, actualMs, baseMs, startTime, commitTime) => {
+  if (actualMs < THRESHOLD_MS) {
+    return
+  }
+
+  ensureLogDir()
+
+  const row = {
+    actualMs: Math.round(actualMs * 100) / 100,
+    baseMs: Math.round(baseMs * 100) / 100,
+    commitMs: Math.round(commitTime * 100) / 100,
+    id,
+    phase,
+    startMs: Math.round(startTime * 100) / 100,
+    ts: Date.now()
+  }
+
+  try {
+    appendFileSync(LOG_PATH, `${JSON.stringify(row)}\n`)
+  } catch {
+    // Same rationale as ensureLogDir — never crash the UI to log a sample.
+  }
+}
+
+export function PerfPane({ children, id }: { children: ReactNode; id: string }) {
+  if (!ENABLED) {
+    return children
+  }
+
+  return (
+    <Profiler id={id} onRender={onRender}>
+      {children}
+    </Profiler>
+  )
+}
+
+export const PERF_ENABLED = ENABLED
+export const PERF_LOG_PATH = LOG_PATH