fix(tui): stop persisting full tool output in trail lines (silent OOM death)

A heavy --tui session (browser snapshots, large tool outputs) silently
OOM-killed the Node parent within minutes — closing the gateway child's
stdin, which the user saw only as a bare "gateway exited" / stdin EOF.
CLI was immune. Root cause: each completed tool's verbose trail line
embedded up to 16KB of result_text, persisted in transcript Msg.tools[]
for the whole session and rendered EXPANDED by default, so an Ink
render-node tree was built for every one of up to 800 messages at once.
That tree blew past Node's heap at a few hundred MB — far below the 2.5GB
memory-monitor exit threshold, so the death was never even attributed.

- text.ts: persisted verbose tool-trail blocks now cap to a small preview
  (VERBOSE_TRAIL_MAX_CHARS=800/12 lines), not the 16KB live-render budget.
  Retained trail strings drop ~17x (12.2MB -> 0.7MB at 800 msgs); the live
  streaming tail still uses the larger LIVE_RENDER budget.
- tui_gateway/server.py: lower the gateway-side verbose text cap to match
  (1KB/16 lines) so we stop shipping output the TUI no longer renders.
- memoryMonitor.ts: derive critical/high thresholds from the real V8 heap
  ceiling (~88%/70%) instead of the hardcoded 2.5GB that killed the process
  at 31% of an 8GB ceiling; add a one-shot onWarn early-warning on fast
  sub-threshold heap growth so the next such death is diagnosable, not silent.
- entry.tsx: wire onWarn to a crash-log breadcrumb + stderr line.

Full tool output is unchanged in the agent context and SQLite session — this
is display/transport only, no behavior or context change.

Fixes #34095. Related #27282.

Tests: ui-tui text + new memoryMonitor suites (33 pass), python verbose-cap
guard (5 pass); full ui-tui suite shows no new failures vs pristine main.
E2E repro confirms the retention drop.

ui-tui/src/entry.tsx

@@ -75,7 +75,17 @@ const stopMemoryMonitor = startMemoryMonitor({
     process.stderr.write('hermes-tui: exiting to avoid OOM; restart to recover\n')
     process.exit(137)
   },
-  onHigh: (snap, dump) => process.stderr.write(dumpNotice(snap, dump))
+  onHigh: (snap, dump) => process.stderr.write(dumpNotice(snap, dump)),
+  // Sub-threshold abnormal heap growth (#34095). The TUI used to die silently
+  // here — Node OOMs from a render-tree blowup well below the exit threshold,
+  // so the only trace was a bare gateway `stdin EOF`. Persist a breadcrumb +
+  // stderr line so the next such death is attributable instead of silent.
+  onWarn: snap => {
+    recordParentLifecycle(`memory-warning fast heap growth heap=${formatBytes(snap.heapUsed)} rss=${formatBytes(snap.rss)}`)
+    process.stderr.write(
+      `hermes-tui: heap climbing fast (${formatBytes(snap.heapUsed)}) — a large tool output or long session may be straining memory\n`
+    )
+  }
 })
 
 if (process.env.HERMES_HEAPDUMP_ON_START === '1') {