fix(sessions): read the composer from a styled capture so a prompt suggestion is not a draft

Claude Code draws its prompt suggestion in an empty composer, the first letter in the reverse-video cursor cell and the rest faint, so a plain capture read it as typed text and keep-warm never nudged those sessions. The keep-warm pane read now uses capture-pane -e and drops the suggestion before checking the composer.

Also from review: an off status carries no window, automation and an unreadable composer retry instead of stopping, a failed evaluation re-arms a retry, a trigger during an evaluation queues one follow-up that remove() cancels, and the cap's clock is seeded from lastSubmitAt for pre-upgrade state.

src/mux-interface.ts

@@ -428,11 +428,12 @@ export interface TerminalMultiplexer extends EventEmitter {
   captureActivePaneBuffer?(muxName: string, opts?: PaneCaptureOptions): string | null;
 
   /**
-   * Plain text of the visible frame: no styles, no cursor query, no repaint
-   * reconstruction. Deliberately cheaper than `capturePaneBuffer` because idle
+   * Plain text of the visible frame: no cursor query, no repaint
+   * reconstruction, and no styles unless `styles` asks for them (SGR only, lines
+   * still `\n`-separated). Deliberately cheaper than `capturePaneBuffer` because idle
    * detection calls it on a timer: it only needs to read what the CLI is
    * currently rendering, never to replay it into an xterm. Returns null when the
    * pane cannot be read.
    */
-  capturePaneText?(muxName: string, paneTarget?: string): string | null;
+  capturePaneText?(muxName: string, paneTarget?: string, opts?: { styles?: boolean }): string | null;
 }