fix(tui): bound retained state against idle OOM

Guards four unbounded growth paths reachable at idle — the shape matches
reports of the TUI hitting V8's 2GB heap limit after ~1m of idle with 0
tokens used (Mark-Compact freed ~6MB of 2045MB → pure retention).

- `GatewayClient.logs` + `gateway.stderr` events: 200-line cap is bytes-
  uncapped; a chatty Python child emitting multi-MB lines (traceback,
  dumped config, unsplit JSON) retains everything. Truncate at 4KB/line.
- `GatewayClient.bufferedEvents`: unbounded until `drain()` fires. Cap
  at 2000 so a pre-mount event storm can't pin memory indefinitely.
- `useMainApp` gateway `exit` handler: didn't reset `turnController`, so
  a mid-stream crash left `bufRef`/`reasoningText` alive forever.
- `pasteSnips` count-capped (32) but byte-uncapped. Add a 4MB total cap
  and clear snips in `clearIn` so submitted pastes don't linger.
- `StylePool.transitionCache`: uncapped `Map<number,string>`. Full-clear
  at 32k entries (mirrors `charCache` pattern).

ui-tui/packages/hermes-ink/src/ink/screen.ts

@@ -121,6 +121,8 @@ const YELLOW_FG_CODE: AnsiCode = {
   endCode: '\x1b[39m'
 }
 
+const MAX_TRANSITION_CACHE = 32768
+
 export class StylePool {
   private ids = new Map<string, number>()
   private styles: AnsiCode[][] = []
@@ -160,7 +162,9 @@ export class StylePool {
   /**
    * Returns the pre-serialized ANSI string to transition from one style to
    * another. Cached by (fromId, toId) — zero allocations after first call
-   * for a given pair.
+   * for a given pair. Full-clear at MAX_TRANSITION_CACHE guards against
+   * unbounded growth from ever-expanding id spaces; cache repopulates from
+   * the next frame's actual transitions.
    */
   transition(fromId: number, toId: number): string {
     if (fromId === toId) {
@@ -171,6 +175,10 @@ export class StylePool {
     let str = this.transitionCache.get(key)
 
     if (str === undefined) {
+      if (this.transitionCache.size >= MAX_TRANSITION_CACHE) {
+        this.transitionCache.clear()
+      }
+
       str = ansiCodesToString(diffAnsiCodes(this.get(fromId), this.get(toId)))
       this.transitionCache.set(key, str)
     }