fix(cli): handle plugin platforms in _get_platform_tools toolset lookup

The static PLATFORMS registry only contains built-in platforms (slack,
discord, etc.). Plugin platforms registered via
PluginContext.register_platform_adapter aren't in PLATFORMS, so the
existing PLATFORMS[platform]["default_toolset"] lookup raised KeyError
during agent loop init for any plugin-platform message.

Caught by an end-to-end test that spawns hermes gateway run + a stub
OpenAI-compat LLM and routes a real message through a plugin platform
(molecule-a2a). Fall back to "hermes-cli" (most permissive in-tree
toolset) for plugin platforms; operators can override per-platform via
config.platform_toolsets.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

gateway/config.py

@@ -90,8 +90,9 @@ class HomeChannel:
     
     @classmethod
     def from_dict(cls, data: Dict[str, Any]) -> "HomeChannel":
+        from hermes_cli.plugins import resolve_platform_id
         return cls(
-            platform=Platform(data["platform"]),
+            platform=resolve_platform_id(data["platform"]),
             chat_id=str(data["chat_id"]),
             name=data.get("name", "Home"),
         )
@@ -228,6 +229,20 @@ class GatewayConfig:
     # Platform configurations
     platforms: Dict[Platform, PlatformConfig] = field(default_factory=dict)
 
+    # Plugin-registered platform configurations.
+    #
+    # Keyed by string platform name (matching what
+    # PluginContext.register_platform_adapter was called with). Populated
+    # by from_dict() when a platform name in config.yaml doesn't map to
+    # a built-in Platform enum value but IS claimed by a loaded plugin.
+    # The gateway runner iterates this dict alongside `platforms` and
+    # creates adapters via _create_plugin_adapter.
+    #
+    # Held as a separate dict (rather than mixing with `platforms`) so
+    # the closed Platform enum stays closed — no synthetic enum members,
+    # no string-vs-enum sniffing throughout the codebase.
+    plugin_platforms: Dict[str, PlatformConfig] = field(default_factory=dict)
+    
     # Session reset policies by type
     default_reset_policy: SessionResetPolicy = field(default_factory=SessionResetPolicy)
     reset_by_type: Dict[str, SessionResetPolicy] = field(default_factory=dict)
@@ -361,13 +376,31 @@ class GatewayConfig:
     
     @classmethod
     def from_dict(cls, data: Dict[str, Any]) -> "GatewayConfig":
+        # Trigger plugin discovery so register_platform_adapter calls
+        # have populated the plugin manager's adapter registry by the
+        # time we look up unknown platform names below. Idempotent.
+        # Imported inside the method to avoid pulling hermes_cli into
+        # gateway.config's import-time dep graph.
+        try:
+            from hermes_cli.plugins import discover_plugins, get_plugin_platform_adapter
+            discover_plugins()
+        except Exception:
+            # Plugin discovery is optional. If hermes_cli isn't on the
+            # path (e.g. some embedded test scenarios), silently fall
+            # back to the original "skip unknown" behavior.
+            get_plugin_platform_adapter = lambda _name: None  # type: ignore[assignment]
+
         platforms = {}
+        plugin_platforms: Dict[str, PlatformConfig] = {}
         for platform_name, platform_data in data.get("platforms", {}).items():
             try:
                 platform = Platform(platform_name)
                 platforms[platform] = PlatformConfig.from_dict(platform_data)
             except ValueError:
-                pass  # Skip unknown platforms
+                # Not a built-in platform. Check if a plugin claims it.
+                if get_plugin_platform_adapter(platform_name) is not None:
+                    plugin_platforms[platform_name] = PlatformConfig.from_dict(platform_data)
+                # Else: silently skip — original behavior preserved.
         
         reset_by_type = {}
         for type_name, policy_data in data.get("reset_by_type", {}).items():
@@ -406,6 +439,7 @@ class GatewayConfig:
 
         return cls(
             platforms=platforms,
+            plugin_platforms=plugin_platforms,
             default_reset_policy=default_policy,
             reset_by_type=reset_by_type,
             reset_by_platform=reset_by_platform,

gateway/run.py

@@ -1953,6 +1953,47 @@ class GatewayRunner:
                     "next_retry": time.monotonic() + 30,
                 }
         
+        # Plugin-registered platforms (after the in-tree loop above —
+        # in-tree wins on name collision because it ran first). Plugin
+        # platforms are NOT in the Platform enum, so they don't get the
+        # full reconnection-queue + status-tracking treatment yet —
+        # that's a v1 simplification. If a plugin platform fails on
+        # connect we log + skip without queueing.
+        for plugin_name, platform_config in self.config.plugin_platforms.items():
+            if not platform_config.enabled:
+                continue
+            enabled_platform_count += 1
+            adapter = self._create_plugin_adapter(plugin_name, platform_config)
+            if not adapter:
+                logger.warning("No adapter available for plugin platform %s", plugin_name)
+                continue
+            adapter.set_message_handler(self._handle_message)
+            adapter.set_fatal_error_handler(self._handle_adapter_fatal_error)
+            adapter.set_session_store(self.session_store)
+            adapter.set_busy_session_handler(self._handle_active_session_busy_message)
+            logger.info("Connecting to plugin platform %s...", plugin_name)
+            try:
+                success = await adapter.connect()
+                if success:
+                    # Key by adapter.platform (a PluginPlatformIdentifier
+                    # instance). Downstream code does ``[p.value for p in
+                    # self.adapters.keys()]`` and similar — keying by the
+                    # identifier (which has a .value attribute) keeps
+                    # plugin platforms structurally compatible with the
+                    # rest of the dict instead of mixing strings and
+                    # enum members.
+                    self.adapters[adapter.platform] = adapter
+                    connected_count += 1
+                    logger.info("✓ %s (plugin) connected", plugin_name)
+                else:
+                    logger.warning("✗ %s (plugin) failed to connect", plugin_name)
+                    startup_retryable_errors.append(
+                        f"{plugin_name}: failed to connect"
+                    )
+            except Exception as e:
+                logger.exception("Plugin platform %s: connect raised", plugin_name)
+                startup_retryable_errors.append(f"{plugin_name}: {e}")
+
         if connected_count == 0:
             if startup_nonretryable_errors:
                 reason = "; ".join(startup_nonretryable_errors)
@@ -2421,6 +2462,47 @@ class GatewayRunner:
         """Wait for shutdown signal."""
         await self._shutdown_event.wait()
     
+    def _create_plugin_adapter(
+        self,
+        name: str,
+        config: Any,
+    ) -> Optional[BasePlatformAdapter]:
+        """Create an adapter from a plugin-registered platform.
+
+        Looks up the plugin's registered (adapter_class, requirements_check)
+        tuple via PluginContext.register_platform_adapter, validates
+        requirements, and instantiates. Returns None on any failure
+        (logs the cause).
+
+        Distinct from _create_adapter to keep the in-tree if/elif chain
+        free of plugin concerns; plugin platforms always go through this
+        path.
+        """
+        from hermes_cli.plugins import get_plugin_platform_adapter
+        entry = get_plugin_platform_adapter(name)
+        if entry is None:
+            logger.warning(
+                "Plugin platform %s: no plugin claims this name. "
+                "Did the plugin's register() function call "
+                "ctx.register_platform_adapter(name=%r, ...)?",
+                name, name,
+            )
+            return None
+        adapter_class, req_check = entry
+        if req_check and not req_check():
+            logger.warning(
+                "Plugin platform %s: requirements_check returned False",
+                name,
+            )
+            return None
+        try:
+            return adapter_class(config)
+        except Exception:
+            logger.exception(
+                "Plugin platform %s: adapter __init__ raised", name,
+            )
+            return None
+
     def _create_adapter(
         self,
         platform: Platform,

gateway/session.py

@@ -123,8 +123,9 @@ class SessionSource:
     
     @classmethod
     def from_dict(cls, data: Dict[str, Any]) -> "SessionSource":
+        from hermes_cli.plugins import resolve_platform_id
         return cls(
-            platform=Platform(data["platform"]),
+            platform=resolve_platform_id(data["platform"]),
             chat_id=str(data["chat_id"]),
             chat_name=data.get("chat_name"),
             chat_type=data.get("chat_type", "dm"),
@@ -409,10 +410,8 @@ class SessionEntry:
         
         platform = None
         if data.get("platform"):
-            try:
-                platform = Platform(data["platform"])
-            except ValueError as e:
-                logger.debug("Unknown platform value %r: %s", data["platform"], e)
+            from hermes_cli.plugins import resolve_platform_id
+            platform = resolve_platform_id(data["platform"])
         
         return cls(
             session_key=data["session_key"],

hermes_cli/plugins.py

@@ -341,6 +341,41 @@ class PluginContext:
         self._manager._hooks.setdefault(hook_name, []).append(callback)
         logger.debug("Plugin %s registered hook: %s", self.manifest.name, hook_name)
 
+    # -- platform adapter registration --------------------------------------
+
+    def register_platform_adapter(
+        self,
+        name: str,
+        adapter_class: type,
+        requirements_check: Callable[[], bool] | None = None,
+    ) -> None:
+        """Register a custom messaging platform adapter.
+
+        ``name`` is the identifier the user puts under
+        ``gateway.platforms.<name>`` in config.yaml. ``adapter_class``
+        must be a subclass of ``gateway.platforms.base.BasePlatformAdapter``.
+        ``requirements_check`` is an optional callable returning False
+        when the adapter's dependencies aren't installed (mirrors the
+        existing ``check_telegram_requirements`` pattern).
+
+        Plugin-registered adapters are consulted as a FALLBACK after
+        ``GatewayRunner._create_adapter`` exhausts its hardcoded chain
+        of in-tree platforms — in-tree wins on name collision so this
+        can't shadow Telegram, Slack, etc.
+        """
+        if name in self._manager._plugin_platform_adapters:
+            logger.warning(
+                "Plugin '%s' tried to register platform adapter '%s' but it is "
+                "already registered by another plugin. Skipping.",
+                self.manifest.name, name,
+            )
+            return
+        self._manager._plugin_platform_adapters[name] = (adapter_class, requirements_check)
+        logger.debug(
+            "Plugin %s registered platform adapter: %s",
+            self.manifest.name, name,
+        )
+
     # -- skill registration -------------------------------------------------
 
     def register_skill(
@@ -407,6 +442,10 @@ class PluginManager:
         self._cli_ref = None  # Set by CLI after plugin discovery
         # Plugin skill registry: qualified name → metadata dict.
         self._plugin_skills: Dict[str, Dict[str, Any]] = {}
+        # Plugin platform adapter registry: name → (adapter_class, optional req_check).
+        # Consulted by GatewayRunner._create_adapter as a fallback after the
+        # in-tree if/elif chain. See PluginContext.register_platform_adapter.
+        self._plugin_platform_adapters: Dict[str, tuple] = {}
 
     # -----------------------------------------------------------------------
     # Public
@@ -790,6 +829,86 @@ def get_plugin_command_handler(name: str) -> Optional[Callable]:
     return entry["handler"] if entry else None
 
 
+def get_plugin_platform_adapter(name: str) -> Optional[tuple]:
+    """Return ``(adapter_class, requirements_check_or_None)`` for a
+    plugin-registered platform adapter, or ``None`` if no plugin claims
+    that platform name.
+
+    Used by ``GatewayRunner._create_adapter`` as a fallback after the
+    in-tree if/elif chain — see ``PluginContext.register_platform_adapter``.
+    """
+    return get_plugin_manager()._plugin_platform_adapters.get(name)
+
+
+class PluginPlatformIdentifier:
+    """Platform-enum-shaped identifier for plugin-registered platforms.
+
+    Built-in adapters pass ``Platform.TELEGRAM`` etc. as the second arg
+    to ``BasePlatformAdapter.__init__``. Plugin adapters can't extend
+    the closed Platform enum, so they pass an instance of this class
+    instead — it quacks like ``Platform`` enough for the base class
+    (``.value`` attribute, hashable, equality on value).
+
+    Usage in a plugin adapter::
+
+        from hermes_cli.plugins import PluginPlatformIdentifier
+        from gateway.platforms.base import BasePlatformAdapter
+
+        class MyAdapter(BasePlatformAdapter):
+            def __init__(self, config):
+                super().__init__(config, PluginPlatformIdentifier("my-platform"))
+
+    The ``name`` should match what was passed to
+    ``ctx.register_platform_adapter(name=..., ...)``.
+    """
+
+    __slots__ = ("value",)
+
+    def __init__(self, name: str):
+        self.value = name
+
+    def __hash__(self) -> int:
+        # Distinct hash bucket so a plugin platform named "telegram"
+        # (impossible — registration is rejected — but defensively)
+        # never collides with Platform.TELEGRAM in dict keys.
+        return hash(("__plugin_platform__", self.value))
+
+    def __eq__(self, other: object) -> bool:
+        return (
+            isinstance(other, PluginPlatformIdentifier)
+            and self.value == other.value
+        )
+
+    def __repr__(self) -> str:
+        return f"PluginPlatformIdentifier({self.value!r})"
+
+
+def resolve_platform_id(value: str):
+    """Resolve a platform-name string to a ``Platform`` enum member or
+    a ``PluginPlatformIdentifier``.
+
+    Used by ``from_dict`` deserializers for ``SessionSource``,
+    ``SessionEntry``, ``HomeChannel`` etc. Without this fallback,
+    daemon restart would lose every session whose platform was
+    contributed by a plugin (e.g., ``molecule-a2a``) because the
+    bare ``Platform(value)`` call raises ``ValueError`` for unknown
+    enum members.
+
+    The fallback is intentionally narrow: an unknown name is only
+    accepted as a plugin identifier if a currently-loaded plugin has
+    actually claimed that name via ``register_platform_adapter``. Bare
+    typos and corrupted state still raise ``ValueError`` as before, so
+    silent state-corruption doesn't slip past restore.
+    """
+    from gateway.config import Platform  # late import to avoid cycle
+    try:
+        return Platform(value)
+    except ValueError:
+        if get_plugin_platform_adapter(value) is not None:
+            return PluginPlatformIdentifier(value)
+        raise
+
+
 def get_plugin_commands() -> Dict[str, dict]:
     """Return the full plugin commands dict (name → {handler, description, plugin}).
 

hermes_cli/tools_config.py

@@ -516,7 +516,15 @@ def _get_platform_tools(
     toolset_names = platform_toolsets.get(platform)
 
     if toolset_names is None or not isinstance(toolset_names, list):
-        default_ts = PLATFORMS[platform]["default_toolset"]
+        # Plugin platforms (registered via PluginContext.register_platform_adapter)
+        # aren't in the static PLATFORMS registry — fall back to the cli
+        # toolset, which is the most permissive in-tree default. Operators
+        # can override per-platform via config.platform_toolsets.
+        platform_info = PLATFORMS.get(platform)
+        if platform_info is None:
+            default_ts = "hermes-cli"
+        else:
+            default_ts = platform_info["default_toolset"]
         toolset_names = [default_ts]
 
     # YAML may parse bare numeric names (e.g. ``12306:``) as int.