Dead code: orphaned functions in core UI/messaging/config (incl. never-fired `on_message` hook)

Summary

Evidence chain

• Static + grep: zero references repo-wide (Python + docs/configs) for all of the above.
• Runtime trace: full suite (11,691 tests), none executed.
• Git history:
  • _get_active_filter_text — leftover from live-filtering PR #262 (ab8e32ce).
  • update_visible_entries — orphaned by PUP-346 / search keybinding rework (#500, 0f8bbfca); its docstring still claims it's "used for the picker's initial setup".
  • clear_observed_quick_resume_paths — unused since quick-resume feature landed (#501).
  • set_smooth_*_stream — the /set menu writes through generic set_config_value(key, ...) (set_menu_catalog.py:499-518); only the getters are consumed (agents/smooth_stream.py).
• ⚠️ on_message: "on_message" is a registered hook name in callbacks.py (lines 46, 101), so plugins can register callbacks for it — but the trigger function on_message() is never called anywhere in the codebase. Registered callbacks silently never fire. This is either dead code to remove or a regression to fix (possibly related to 26d831cd "remove browser terminal subsystem and REST API").
• _render_message_immediate docstring says "Public-ish for tests/teardown" — but no test or teardown path calls it.
• remove_steer_queue_listener: the matching add_steer_queue_listener IS used (plugins/steer_queue/register_callbacks.py:114) but nothing ever unregisters — either wire up cleanup or drop the method.

Caveats

• config.py setters are public API of a published package; external consumers possible.
• Decide on_message intent (fix vs. remove) before deleting.

Verification

pytest tests/ -q --no-cov

Filed by dead-code-detective-9a7d4c. Findings are read-only analysis; deletion requires human review.

Review the listed symbols in code_puppy/command_line, code_puppy/messaging, code_puppy/config.py, and code_puppy/callbacks.py, starting with the reported repository-wide references and git history. Resolve whether on_message should be fixed or removed and assess the public config setters before changing them. Done means the approved dead code is removed or repaired, with pytest tests/ -q --no-cov passing.