Merge pull request #601: fix(terminal): load a shell from tmux's rendered history, not the byte recording

Conflicts resolved against #583 and #588:
- One history-depth field: #583's `historyLines` / `capturedHistoryLines`
  (reported as `paneHistoryLines`) is kept, and #601's lines cut now reads it
  instead of a second `capturedHistorySize`. #601's `alternateOn` /
  `capturedAlternateOn` joins it, and the one display-message format string
  ends `#{history_size} #{alternate_on}`.
- selectSession keeps #588's full=1 switch for panes with no scrollback, gated
  off remote and Docker sessions, and #601's SHELL_LOAD_QUERY for shells.
- computeHistoryTruncationNotice names a line count when paneHistoryLines is
  known (#583) and otherwise uses #601's remainder wording.
- docs: api-reference lists both historyLinesCut and paneHistoryLines; the
  notice invariant keys on history_size while the shell's automatic load is
  the one place alternate_on decides.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/mux-interface.ts

@@ -210,9 +210,18 @@ export interface PaneCaptureOptions {
    * same query as the geometry. 0 means a full-history capture can return
    * nothing beyond the visible frame: a pane in the alternate screen (a
    * fullscreen CLI that keeps its transcript itself) never accumulates any.
-   * Absent when the pane could not be queried.
+   * A full-history capture bounded by `historyLimitLines` below this depth
+   * left older lines behind in the multiplexer, which the caller must report
+   * as recoverable. Absent when the pane could not be queried.
    */
   capturedHistoryLines?: number;
+  /**
+   * Filled in by the implementation with whether the pane was in the alternate
+   * screen at capture time, when it can tell. tmux keeps no history for such a
+   * pane (a nested tmux client puts it there), so a full-history capture of it
+   * holds one screen plus whatever the pane held before.
+   */
+  capturedAlternateOn?: boolean;
 }
 
 /**