feat: Core Plugin system — is_core flag, topological sort dependency resolution, deactivation protection

app/main.py

@@ -112,7 +112,7 @@ async def lifespan(app: FastAPI):
     async_session = async_sessionmaker(get_engine(), expire_on_commit=False)
 
     async with async_session() as db:
-        for name in registry._plugins:
+        for name in registry.resolve_load_order():
             plugin = registry.get_plugin(name)
             if plugin is None:
                 continue
@@ -131,6 +131,7 @@ async def lifespan(app: FastAPI):
                     version=plugin.manifest.version,
                     status="installed",
                     active=True,
+                    is_core=plugin.manifest.is_core,
                 )
                 db.add(plugin_record)
                 await db.flush()

app/models/plugin.py

@@ -31,6 +31,7 @@ class Plugin(Base, TimestampMixin):
     status: Mapped[str] = mapped_column(String(20), nullable=False, default="installed")
     installed: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
     active: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
+    is_core: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
     config: Mapped[dict[str, Any] | None] = mapped_column(
         Text,
         nullable=True,  # JSON string for plugin configuration

app/plugins/builtins/entity_links/plugin.py

@@ -37,6 +37,7 @@ class EntityLinksPlugin(BasePlugin):
         events=["company.deleted", "contact.deleted"],
         migrations=["0001_initial.sql"],
         permissions=[],
+        is_core=True,
     )
 
     async def on_company_deleted(self, payload: dict[str, Any]) -> None:

app/plugins/builtins/permissions/plugin.py

@@ -30,4 +30,5 @@ class PermissionsPlugin(BasePlugin):
         events=[],
         migrations=["0001_initial.sql"],
         permissions=[],
+        is_core=True,
     )

app/plugins/builtins/tags/plugin.py

@@ -25,4 +25,5 @@ class TagsPlugin(BasePlugin):
         events=[],
         migrations=["0001_initial.sql"],
         permissions=[],
+        is_core=True,
     )

app/plugins/manifest.py

@@ -39,6 +39,9 @@ class PluginManifest(BaseModel):
     permissions: list[str] = Field(
         default_factory=list, description="Required permissions for this plugin"
     )
+    is_core: bool = Field(
+        default=False, description="Whether this is a core plugin that cannot be deactivated"
+    )
 
     @field_validator("name")
     @classmethod

app/plugins/registry.py

@@ -180,6 +180,78 @@ class PluginRegistry:
                 f"Activate them first."
             )
 
+    # ── Topological Sort & Dependents ──
+
+    def resolve_load_order(self) -> list[str]:
+        """Return plugin names in dependency-aware load order using Kahn's algorithm.
+
+        Core plugins (is_core=True) are emitted first, then non-core plugins
+        in topological order based on declared dependencies.
+
+        Raises RuntimeError on circular dependencies or missing dependencies.
+        """
+        names = set(self._plugins.keys())
+
+        # Validate that all declared dependencies exist in the registry
+        for name in names:
+            plugin = self._plugins[name]
+            for dep in plugin.manifest.dependencies:
+                if dep not in names:
+                    raise RuntimeError(
+                        f"Plugin '{name}' depends on '{dep}' which is not discovered. "
+                        f"Available plugins: {', '.join(sorted(names))}"
+                    )
+
+        # Build adjacency: dep -> list of plugins that depend on it
+        # and in-degree: plugin -> count of unsatisfied dependencies
+        in_degree: dict[str, int] = {name: 0 for name in names}
+        dependents_map: dict[str, list[str]] = {name: [] for name in names}
+
+        for name in names:
+            plugin = self._plugins[name]
+            for dep in plugin.manifest.dependencies:
+                dependents_map[dep].append(name)
+                in_degree[name] += 1
+
+        # Single Kahn pass with priority: core plugins before non-core at each level.
+        # Queue entries are tuples: (priority, name) where priority 0 = core, 1 = non-core.
+        import heapq
+
+        heap: list[tuple[int, str]] = []
+        for name in names:
+            if in_degree[name] == 0:
+                priority = 0 if self._plugins[name].manifest.is_core else 1
+                heapq.heappush(heap, (priority, name))
+
+        result: list[str] = []
+        while heap:
+            _, current = heapq.heappop(heap)
+            result.append(current)
+            for dependent in dependents_map[current]:
+                in_degree[dependent] -= 1
+                if in_degree[dependent] == 0:
+                    priority = 0 if self._plugins[dependent].manifest.is_core else 1
+                    heapq.heappush(heap, (priority, dependent))
+
+        if len(result) != len(names):
+            unresolved = names - set(result)
+            raise RuntimeError(
+                f"Circular dependency detected among plugins: {', '.join(sorted(unresolved))}"
+            )
+
+        return result
+
+    def get_dependents(self, name: str) -> list[str]:
+        """Return list of discovered plugin names that depend on the given plugin.
+
+        This examines manifest.dependencies of all discovered plugins.
+        """
+        dependents: list[str] = []
+        for plugin_name, plugin in self._plugins.items():
+            if name in plugin.manifest.dependencies:
+                dependents.append(plugin_name)
+        return sorted(dependents)
+
     # ── Permission Validation (soft check) ──
 
     def _check_permissions(self, name: str) -> list[str]:
@@ -289,6 +361,7 @@ class PluginRegistry:
             status="installed",
             installed=True,
             active=False,
+            is_core=plugin.manifest.is_core,
         )
         db.add(record)
         await db.flush()
@@ -370,6 +443,26 @@ class PluginRegistry:
         if not record.active and record.status == "inactive":
             return record
 
+        # Reject deactivation of core plugins
+        if plugin.manifest.is_core or record.is_core:
+            raise ValueError(
+                f"Plugin '{name}' is a core plugin and cannot be deactivated"
+            )
+
+        # Reject deactivation if other active plugins depend on it
+        dependents = self.get_dependents(name)
+        active_dependents: list[str] = []
+        for dep_name in dependents:
+            dep_record = await self._get_plugin_record(db, dep_name)
+            if dep_record is not None and dep_record.active:
+                active_dependents.append(dep_name)
+
+        if active_dependents:
+            raise ValueError(
+                f"Plugin '{name}' cannot be deactivated because active plugins "
+                f"depend on it: {', '.join(active_dependents)}"
+            )
+
         # Call on_deactivate hook (unregisters event listeners)
         await plugin.on_deactivate(db, self._container, self._event_bus)