refactor: remove dead code — 1,784 lines across 77 files (#9180)

Deep scan with vulture, pyflakes, and manual cross-referencing identified:
- 41 dead functions/methods (zero callers in production)
- 7 production-dead functions (only test callers, tests deleted)
- 5 dead constants/variables
- ~35 unused imports across agent/, hermes_cli/, tools/, gateway/

Categories of dead code removed:
- Refactoring leftovers: _set_default_model, _setup_copilot_reasoning_selection,
  rebuild_lookups, clear_session_context, get_logs_dir, clear_session
- Unused API surface: search_models_dev, get_pricing, skills_categories,
  get_read_files_summary, clear_read_tracker, menu_labels, get_spinner_list
- Dead compatibility wrappers: schedule_cronjob, list_cronjobs, remove_cronjob
- Stale debug helpers: get_debug_session_info copies in 4 tool files
  (centralized version in debug_helpers.py already exists)
- Dead gateway methods: send_emote, send_notice (matrix), send_reaction
  (bluebubbles), _normalize_inbound_text (feishu), fetch_room_history
  (matrix), _start_typing_indicator (signal), parse_feishu_post_content
- Dead constants: NOUS_API_BASE_URL, SKILLS_TOOL_DESCRIPTION,
  FILE_TOOLS, VALID_ASPECT_RATIOS, MEMORY_DIR
- Unused UI code: _interactive_provider_selection,
  _interactive_model_selection (superseded by prompt_toolkit picker)

Test suite verified: 609 tests covering affected files all pass.
Tests for removed functions deleted. Tests using removed utilities
(clear_read_tracker, MEMORY_DIR) updated to use internal APIs directly.

tools/skills_tool.py

@@ -447,10 +447,6 @@ def _get_category_from_path(skill_path: Path) -> Optional[str]:
     return None
 
 
-# Token estimation — use the shared implementation from model_metadata.
-from agent.model_metadata import estimate_tokens_rough as _estimate_tokens
-
-
 def _parse_tags(tags_value) -> List[str]:
     """
     Parse tags from frontmatter value.
@@ -629,85 +625,6 @@ def _load_category_description(category_dir: Path) -> Optional[str]:
         return None
 
 
-def skills_categories(verbose: bool = False, task_id: str = None) -> str:
-    """
-    List available skill categories with descriptions (progressive disclosure tier 0).
-
-    Returns category names and descriptions for efficient discovery before drilling down.
-    Categories can have a DESCRIPTION.md file with a description frontmatter field
-    or first paragraph to explain what skills are in that category.
-
-    Args:
-        verbose: If True, include skill counts per category (default: False, but currently always included)
-        task_id: Optional task identifier used to probe the active backend
-
-    Returns:
-        JSON string with list of categories and their descriptions
-    """
-    try:
-        # Use module-level SKILLS_DIR (respects monkeypatching) + external dirs
-        all_dirs = [SKILLS_DIR] if SKILLS_DIR.exists() else []
-        try:
-            from agent.skill_utils import get_external_skills_dirs
-            all_dirs.extend(d for d in get_external_skills_dirs() if d.exists())
-        except Exception:
-            pass
-        if not all_dirs:
-            return json.dumps(
-                {
-                    "success": True,
-                    "categories": [],
-                    "message": "No skills directory found.",
-                },
-                ensure_ascii=False,
-            )
-
-        category_dirs = {}
-        category_counts: Dict[str, int] = {}
-        for scan_dir in all_dirs:
-            for skill_md in scan_dir.rglob("SKILL.md"):
-                if any(part in _EXCLUDED_SKILL_DIRS for part in skill_md.parts):
-                    continue
-
-                try:
-                    frontmatter, _ = _parse_frontmatter(
-                        skill_md.read_text(encoding="utf-8")[:4000]
-                    )
-                except Exception:
-                    frontmatter = {}
-
-                if not skill_matches_platform(frontmatter):
-                    continue
-
-                category = _get_category_from_path(skill_md)
-                if category:
-                    category_counts[category] = category_counts.get(category, 0) + 1
-                    if category not in category_dirs:
-                        category_dirs[category] = skill_md.parent.parent
-
-        categories = []
-        for name in sorted(category_dirs.keys()):
-            category_dir = category_dirs[name]
-            description = _load_category_description(category_dir)
-
-            cat_entry = {"name": name, "skill_count": category_counts[name]}
-            if description:
-                cat_entry["description"] = description
-            categories.append(cat_entry)
-
-        return json.dumps(
-            {
-                "success": True,
-                "categories": categories,
-                "hint": "If a category is relevant to your task, use skills_list with that category to see available skills",
-            },
-            ensure_ascii=False,
-        )
-
-    except Exception as e:
-        return tool_error(str(e), success=False)
-
-
 def skills_list(category: str = None, task_id: str = None) -> str:
     """
     List all available skills (progressive disclosure tier 1 - minimal metadata).
@@ -1240,19 +1157,6 @@ def skill_view(name: str, file_path: str = None, task_id: str = None) -> str:
         return tool_error(str(e), success=False)
 
 
-# Tool description for model_tools.py
-SKILLS_TOOL_DESCRIPTION = """Access skill documents providing specialized instructions, guidelines, and executable knowledge.
-
-Progressive disclosure workflow:
-1. skills_list() - Returns metadata (name, description, tags, linked_file_count) for all skills
-2. skill_view(name) - Loads full SKILL.md content + shows available linked_files
-3. skill_view(name, file_path) - Loads specific linked file (e.g., 'references/api.md', 'scripts/train.py')
-
-Skills may include:
-- references/: Additional documentation, API specs, examples
-- templates/: Output formats, config files, boilerplate code
-- assets/: Supplementary files (agentskills.io standard)
-- scripts/: Executable helpers (Python, shell scripts)"""
 
 
 if __name__ == "__main__":