refactor(tools): decorator-based tool registry replaces monolithic tools.py

Split 2566-line tools.py into a tools/ package with @tool decorator
registration. Each tool's schema, metadata, and implementation live
together. Briefing eligibility is now a briefing=True flag instead of
a separate frozenset allowlist. Conditional inclusion (CalDAV, SearXNG)
uses requires= metadata. Public API (get_tools_for_user, execute_tool)
unchanged.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/fabledassistant/services/tools/rag.py

@@ -0,0 +1,63 @@
+"""RAG scope and calculation tools."""
+
+from __future__ import annotations
+
+from fabledassistant.services.tools._registry import tool
+
+
+@tool(
+    name="set_rag_scope",
+    description="Change the RAG scope for this conversation. Use project_id=<int> to scope to a project, project_id=null to scope to orphan notes only, project_id=-1 for all notes.",
+    parameters={
+        "project_id": {"type": ["integer", "null"], "description": "Project ID to scope to, null for orphan-only, -1 for all notes"},
+    },
+    required=["project_id"],
+)
+async def set_rag_scope_tool(*, user_id, arguments, conv_id=None, workspace_project_id=None, **_ctx):
+    if workspace_project_id is not None:
+        return {"success": False, "error": "Cannot change RAG scope in workspace view"}
+    if conv_id is None:
+        return {"success": False, "error": "No conversation context available"}
+    project_id = arguments.get("project_id")
+    if project_id is not None and project_id != -1:
+        from fabledassistant.services.projects import get_project
+        proj = await get_project(user_id, int(project_id))
+        if proj is None:
+            return {"success": False, "error": "Project not found"}
+        scope_label = proj.title
+    elif project_id == -1:
+        scope_label = "All notes"
+    else:
+        scope_label = "Orphan notes only"
+    from fabledassistant.services.chat import update_conversation
+    await update_conversation(user_id, conv_id, rag_project_id=project_id)
+    return {"success": True, "type": "rag_scope_set", "scope_label": scope_label}
+
+
+@tool(
+    name="calculate",
+    description=(
+        "Evaluate a mathematical expression and return the exact result. Use this for any "
+        "arithmetic, percentages, unit conversions, or multi-step calculations where precision "
+        "matters. Supports standard math operators (+, -, *, /, **, %) and all Python math "
+        "module functions (sqrt, log, sin, cos, floor, ceil, etc.)."
+    ),
+    parameters={
+        "expression": {"type": "string", "description": "A valid Python math expression (e.g. '(450 * 1.13) / 12', 'sqrt(144)', 'log(1000, 10)')"},
+    },
+    required=["expression"],
+)
+async def calculate_tool(*, user_id, arguments, **_ctx):
+    import math as _math
+
+    expr = str(arguments.get("expression", "")).strip()
+    if not expr:
+        return {"success": False, "error": "expression is required"}
+    allowed_names = {k: v for k, v in vars(_math).items() if not k.startswith("_")}
+    allowed_names["abs"] = abs
+    allowed_names["round"] = round
+    try:
+        result = eval(expr, {"__builtins__": {}}, allowed_names)  # noqa: S307
+    except Exception as calc_err:
+        return {"success": False, "error": f"Could not evaluate expression: {calc_err}"}
+    return {"success": True, "type": "calculation", "data": {"expression": expr, "result": result}}