feat: named server sets — save/apply the Active/Disabled split (#52)

Sets live in the config under _bccServerSets (bcc-owned, ignored by
Claude, travels with the file). Apply enables exactly the set's members
and parks the rest; vanished members are reported, not fatal. GUI row:
set combo + Apply + Save set… + delete.

Closes #52

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_core.py

@@ -769,6 +769,68 @@ def test_args_secret_warning_empty():
     assert c.args_secret_warning({"args": []}) is None
 
 
+# --------------------------------------------------------------------------- #
+# Named server sets (issue #52)
+# --------------------------------------------------------------------------- #
+def _three_servers():
+    return [
+        c.ServerEntry("alpha", {"command": "npx"}, True),
+        c.ServerEntry("beta", {"command": "uvx"}, True),
+        c.ServerEntry("gamma", {"url": "https://x.example/mcp"}, False),
+    ]
+
+
+def test_save_and_list_server_sets_roundtrip():
+    cfg: dict = {}
+    members = c.save_server_set(cfg, "webdev", _three_servers())
+    assert members == ["alpha", "beta"]  # only the enabled ones
+    assert c.list_server_sets(cfg) == {"webdev": ["alpha", "beta"]}
+
+
+def test_apply_server_set_enables_exactly_the_members():
+    servers = _three_servers()
+    missing = c.apply_server_set(servers, ["gamma"])
+    assert missing == []
+    assert [s.enabled for s in servers] == [False, False, True]
+
+
+def test_apply_server_set_reports_missing_members():
+    servers = _three_servers()
+    missing = c.apply_server_set(servers, ["alpha", "vanished", "gone"])
+    assert missing == ["gone", "vanished"]
+    assert [s.enabled for s in servers] == [True, False, False]  # rest still applied
+
+
+def test_delete_server_set_drops_empty_key():
+    cfg: dict = {}
+    c.save_server_set(cfg, "only", _three_servers())
+    assert c.delete_server_set(cfg, "only") is True
+    assert c.SETS_KEY not in cfg  # no empty bcc key left behind
+    assert c.delete_server_set(cfg, "only") is False
+
+
+def test_server_sets_survive_write_and_reload(tmp_path):
+    cfgpath = tmp_path / "cfg.json"
+    cfg = {"mcpServers": {"alpha": {"command": "npx"}}}
+    c.save_server_set(cfg, "webdev", [c.ServerEntry("alpha", {"command": "npx"}, True)])
+    c.write_config(cfgpath, cfg)
+    reloaded = c.load_config(cfgpath)
+    assert c.list_server_sets(reloaded) == {"webdev": ["alpha"]}
+
+
+def test_apply_servers_preserves_sets_key():
+    cfg: dict = {"mcpServers": {}}
+    c.save_server_set(cfg, "s", [c.ServerEntry("alpha", {"command": "npx"}, True)])
+    c.apply_servers(cfg, _three_servers())
+    assert c.SETS_KEY in cfg  # the server writer never touches sets
+
+
+def test_list_server_sets_skips_malformed_entries():
+    cfg = {c.SETS_KEY: {"good": ["a"], "bad-not-list": "a", "bad-items": ["a", 3]}}
+    assert c.list_server_sets(cfg) == {"good": ["a"]}
+    assert c.list_server_sets({c.SETS_KEY: "junk"}) == {}
+
+
 # --------------------------------------------------------------------------- #
 # resolve_name_collision (paste/import duplicate-name handling — issue #8)
 # --------------------------------------------------------------------------- #