feat: add multi-server support

Connect to multiple IRC servers concurrently from a single config file.
Plugins are loaded once and shared; per-server state is isolated via
separate SQLite databases and per-bot runtime state (bot._pstate).

- Add build_server_configs() for [servers.*] config layout
- Bot.__init__ gains name parameter, _pstate dict for plugin isolation
- cli.py runs multiple bots via asyncio.gather
- 9 stateful plugins migrated from module-level dicts to _ps(bot) pattern
- Backward compatible: legacy [server] config works unchanged

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

tests/test_config.py

@@ -5,7 +5,14 @@ from pathlib import Path
 
 import pytest
 
-from derp.config import DEFAULTS, _merge, load, resolve_config
+from derp.config import (
+    DEFAULTS,
+    _merge,
+    _server_name,
+    build_server_configs,
+    load,
+    resolve_config,
+)
 
 
 class TestMerge:
@@ -110,3 +117,166 @@ class TestResolveConfig:
         original = copy.deepcopy(DEFAULTS)
         resolve_config(None)
         assert DEFAULTS == original
+
+
+# ---------------------------------------------------------------------------
+# _server_name
+# ---------------------------------------------------------------------------
+
+
+class TestServerName:
+    """Test hostname-to-short-name derivation."""
+
+    def test_libera(self):
+        assert _server_name("irc.libera.chat") == "libera"
+
+    def test_oftc(self):
+        assert _server_name("irc.oftc.net") == "oftc"
+
+    def test_freenode(self):
+        assert _server_name("chat.freenode.net") == "freenode"
+
+    def test_plain_hostname(self):
+        assert _server_name("myserver") == "myserver"
+
+    def test_empty_fallback(self):
+        assert _server_name("") == ""
+
+    def test_only_common_parts(self):
+        assert _server_name("irc.chat.irc") == "irc.chat.irc"
+
+
+# ---------------------------------------------------------------------------
+# build_server_configs
+# ---------------------------------------------------------------------------
+
+
+class TestBuildServerConfigs:
+    """Test multi-server config builder."""
+
+    def test_legacy_single_server(self):
+        """Legacy [server] config returns a single-entry dict."""
+        raw = _merge(DEFAULTS, {
+            "server": {"host": "irc.libera.chat", "nick": "testbot"},
+        })
+        result = build_server_configs(raw)
+        assert list(result.keys()) == ["libera"]
+        assert result["libera"]["server"]["nick"] == "testbot"
+
+    def test_legacy_preserves_full_config(self):
+        """Legacy mode passes through the entire config dict."""
+        raw = _merge(DEFAULTS, {
+            "server": {"host": "irc.oftc.net"},
+            "bot": {"prefix": "."},
+        })
+        result = build_server_configs(raw)
+        cfg = result["oftc"]
+        assert cfg["bot"]["prefix"] == "."
+        assert cfg["server"]["host"] == "irc.oftc.net"
+
+    def test_multi_server_creates_entries(self):
+        """Multiple [servers.*] blocks produce multiple entries."""
+        raw = {
+            "bot": {"prefix": "!", "channels": [], "plugins_dir": "plugins"},
+            "servers": {
+                "libera": {"host": "irc.libera.chat", "port": 6697,
+                           "nick": "derp", "channels": ["#test"]},
+                "oftc": {"host": "irc.oftc.net", "port": 6697,
+                         "nick": "derpbot", "channels": ["#derp"]},
+            },
+        }
+        result = build_server_configs(raw)
+        assert set(result.keys()) == {"libera", "oftc"}
+
+    def test_multi_server_key_separation(self):
+        """Server keys and bot keys are separated correctly."""
+        raw = {
+            "servers": {
+                "test": {
+                    "host": "irc.test.net", "port": 6667, "tls": False,
+                    "nick": "bot",
+                    "prefix": ".", "channels": ["#a"],
+                    "admins": ["*!*@admin"],
+                },
+            },
+        }
+        result = build_server_configs(raw)
+        cfg = result["test"]
+        # Server keys
+        assert cfg["server"]["host"] == "irc.test.net"
+        assert cfg["server"]["port"] == 6667
+        assert cfg["server"]["nick"] == "bot"
+        # Bot keys (overrides)
+        assert cfg["bot"]["prefix"] == "."
+        assert cfg["bot"]["channels"] == ["#a"]
+        assert cfg["bot"]["admins"] == ["*!*@admin"]
+
+    def test_multi_server_inherits_shared_bot(self):
+        """Per-server configs inherit shared [bot] defaults."""
+        raw = {
+            "bot": {"prefix": ".", "admins": ["*!*@global"]},
+            "servers": {
+                "s1": {"host": "irc.s1.net", "nick": "bot1"},
+            },
+        }
+        result = build_server_configs(raw)
+        cfg = result["s1"]
+        assert cfg["bot"]["prefix"] == "."
+        assert cfg["bot"]["admins"] == ["*!*@global"]
+
+    def test_multi_server_overrides_shared_bot(self):
+        """Per-server bot keys override shared [bot] values."""
+        raw = {
+            "bot": {"prefix": "!", "admins": ["*!*@global"]},
+            "servers": {
+                "s1": {"host": "irc.s1.net", "nick": "bot1",
+                       "prefix": ".", "admins": ["*!*@local"]},
+            },
+        }
+        result = build_server_configs(raw)
+        cfg = result["s1"]
+        assert cfg["bot"]["prefix"] == "."
+        assert cfg["bot"]["admins"] == ["*!*@local"]
+
+    def test_multi_server_defaults_applied(self):
+        """Missing keys fall back to DEFAULTS."""
+        raw = {
+            "servers": {
+                "minimal": {"host": "irc.min.net", "nick": "m"},
+            },
+        }
+        result = build_server_configs(raw)
+        cfg = result["minimal"]
+        assert cfg["server"]["tls"] is True  # from DEFAULTS
+        assert cfg["bot"]["prefix"] == "!"   # from DEFAULTS
+        assert cfg["bot"]["rate_limit"] == 2.0
+
+    def test_multi_server_shared_sections(self):
+        """Shared webhook/logging sections propagate to all servers."""
+        raw = {
+            "webhook": {"enabled": True, "port": 9090},
+            "logging": {"format": "json"},
+            "servers": {
+                "a": {"host": "irc.a.net", "nick": "a"},
+                "b": {"host": "irc.b.net", "nick": "b"},
+            },
+        }
+        result = build_server_configs(raw)
+        for name in ("a", "b"):
+            assert result[name]["webhook"]["enabled"] is True
+            assert result[name]["webhook"]["port"] == 9090
+            assert result[name]["logging"]["format"] == "json"
+
+    def test_empty_servers_section_falls_back(self):
+        """Empty [servers] section treated as legacy single-server."""
+        raw = _merge(DEFAULTS, {"servers": {}})
+        result = build_server_configs(raw)
+        assert len(result) == 1
+
+    def test_no_servers_key_is_legacy(self):
+        """Config without [servers] is legacy single-server mode."""
+        raw = copy.deepcopy(DEFAULTS)
+        result = build_server_configs(raw)
+        assert len(result) == 1
+        name = list(result.keys())[0]
+        assert result[name] is raw