docs(control-mode): Note env reqs and capture normalization in CHANGES

Author: tony

CHANGES

@@ -49,13 +49,23 @@ _Future release notes will be placed here_
   existing session if found, otherwise creates a new detached session. Simplifies
   common session reuse patterns and works transparently with both subprocess and
   control-mode engines.
+- Control-mode diagnostics: bounded notification queue with drop counting,
+  richer exceptions (`ControlModeTimeout`, `ControlModeProtocolError`,
+  `ControlModeConnectionError`, `SubprocessTimeout`), and documented retry/timeout
+  behaviour. Control sandbox pytest fixture provides a hermetic control-mode server
+  for integration tests.
 
 ### Compatibility
 
 - Control mode's internal session is now automatically filtered from user-facing APIs.
   Code that previously filtered `libtmux_control_mode` manually can be simplified.
   APIs remain unchanged for tmux command return objects; new metadata is attached for
   advanced users. (#605)
+- `-e KEY=VAL` environment propagation for `new-session`, `new-window`, and
+  `split-window` requires tmux 3.2 or newer. Older tmux versions ignore `-e`; libtmux
+  logs a warning and skips env-specific tests in that configuration.
+- Control-mode `capture-pane` trims trailing whitespace-only lines to align with
+  subprocess behaviour; explicit range flags (`-S/-E`) remain exact.
 
 ### Testing