feat(circles): add update_circle tool (v0.7.4)

Implements accupdatefamily endpoint (verified via FW_DEBUG=1):
- Parameter 'scope' targets any circle (primary or secondary)
- Without scope: renames the primary circle (API default)
- Server always capitalises the first letter of the new name
- Verifies circle existence via famlistfamily in same session
- Response a00.r.r = full circle object with updated name

Also corrects SPEC.md: accupdatefamily with scope= works for any
circle, not just the primary (previous note was incomplete).

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

src/mcp_familywall/server.py

@@ -1342,6 +1342,96 @@ def create_circle(name: str) -> str:
     )
 
 
+# ---------------------------------------------------------------------------
+# Tool: update_circle
+# ---------------------------------------------------------------------------
+
+
+@mcp.tool()
+def update_circle(circle_id: str, name: str) -> str:
+    """Rename a Family Wall circle.
+
+    IMPORTANT: Ask the user for confirmation before calling this tool.
+
+    Only the circle name can be changed via the API.  Note that the server
+    always capitalises the first letter of the new name.
+
+    Args:
+        circle_id: Circle metaId from ``get_circles``
+            (e.g. ``"family/23431854"``).
+        name: New display name for the circle.
+
+    Returns:
+        JSON with ``{updated, id, name}`` on success, or an error message.
+    """
+    if not name or not name.strip():
+        return "Error: 'name' must not be empty."
+
+    try:
+        email, password = get_credentials()
+    except RuntimeError as exc:
+        return f"Error: {exc}"
+
+    try:
+        with FamilyWallClient() as client:
+            client.login(email, password)
+
+            # Verify the circle exists before attempting the update.
+            circles_data = client.call("famlistfamily")
+            try:
+                raw_circles: list[dict[str, Any]] = circles_data["a00"]["r"]["r"]
+                if not isinstance(raw_circles, list):
+                    raise TypeError("a00.r.r is not a list")
+            except (KeyError, TypeError):
+                client.logout()
+                return "Error: Unexpected famlistfamily response structure."
+
+            target = next((c for c in raw_circles if c.get("metaId") == circle_id), None)
+            if target is None:
+                client.logout()
+                available = [c.get("metaId") for c in raw_circles]
+                return json.dumps(
+                    {
+                        "error": f"Circle not found: {circle_id!r}",
+                        "available_circles": available,
+                    },
+                    ensure_ascii=False,
+                    indent=2,
+                )
+
+            # Rename the circle.
+            # Verified: accupdatefamily with scope=<circle_metaId> targets any circle,
+            # both primary and secondary. The server capitalises the first letter.
+            resp = client.call("accupdatefamily", {"scope": circle_id, "name": name})
+            client.logout()
+    except FamilyWallError as exc:
+        return f"Error: Family Wall API error: {exc}"
+    except Exception as exc:
+        return f"Error: Connection error: {exc}"
+
+    # Response: a00.r.r = full circle object
+    try:
+        circle_obj: dict[str, Any] = resp["a00"]["r"]["r"]
+        if not isinstance(circle_obj, dict) or "metaId" not in circle_obj:
+            raise TypeError("unexpected shape")
+    except (KeyError, TypeError):
+        return json.dumps(
+            {"warning": "Unexpected accupdatefamily response structure", "raw": resp},
+            ensure_ascii=False,
+            indent=2,
+        )
+
+    return json.dumps(
+        {
+            "updated": True,
+            "id": circle_obj.get("metaId"),
+            "name": circle_obj.get("name"),
+        },
+        ensure_ascii=False,
+        indent=2,
+    )
+
+
 # ---------------------------------------------------------------------------
 # Tool: add_member_to_circle
 # ---------------------------------------------------------------------------