feat: add AI generation service for network diagrams

Adds network_diagram_ai_service.py with generate_diagram() function that
calls the AI provider to convert plain-English network descriptions into
structured DiagramNode/DiagramEdge data. Registers the action in
ACTION_MODEL_MAP as a standard-tier route.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/core/config.py

@@ -128,6 +128,7 @@ class Settings(BaseSettings):
         "variable_inference": "fast",
         "kb_convert": "standard",
         "script_build": "standard",
+        "network_diagram_generate": "standard",
     }
 
     def get_model_for_action(self, action_type: str) -> str:

backend/app/services/network_diagram_ai_service.py

@@ -0,0 +1,146 @@
+"""AI service for generating network diagrams from natural language."""
+import json
+import logging
+
+from app.core.ai_provider import get_ai_provider
+from app.core.config import settings
+from app.schemas.network_diagram import (
+    AIGenerateRequest,
+    AIGenerateResponse,
+    DiagramNode,
+    DiagramEdge,
+    DeviceProperties,
+)
+
+logger = logging.getLogger(__name__)
+
+SYSTEM_PROMPT_TEMPLATE = """You are a network diagram generator for MSP engineers.
+Given a plain English description of a network, you must return ONLY valid JSON with no markdown, no explanation, no preamble.
+
+Return this exact structure:
+{{
+  "nodes": [
+    {{
+      "id": "unique-string",
+      "type": "device-type-slug",
+      "label": "device label",
+      "position": {{ "x": number, "y": number }},
+      "properties": {{
+        "hostname": "string or null",
+        "ip": "string or null",
+        "subnet": "string or null",
+        "vendor": "string or null",
+        "model": "string or null",
+        "role": "string or null",
+        "vlan": "string or null",
+        "notes": "string or null",
+        "status": "unknown"
+      }}
+    }}
+  ],
+  "edges": [
+    {{
+      "id": "unique-string",
+      "source": "node-id",
+      "target": "node-id",
+      "label": "connection label or null",
+      "connectionType": "ethernet|fiber|wifi|vpn|vlan|wan",
+      "speed": "string or null",
+      "notes": "string or null"
+    }}
+  ],
+  "suggestedName": "short descriptive diagram name",
+  "notes": "any important assumptions or missing info, or null"
+}}
+
+Available device type slugs: {available_slugs}
+
+Position nodes thoughtfully in a logical network topology layout.
+Use x/y coordinates between 0 and 1200 for x, 0 and 800 for y.
+Place WAN/internet at top, core network in middle, endpoints at bottom.
+{merge_instructions}"""
+
+MERGE_INSTRUCTIONS = """
+IMPORTANT: You are ADDING devices to an existing diagram. Do NOT replace existing devices.
+The existing diagram occupies this bounding box: minX={minX}, maxX={maxX}, minY={minY}, maxY={maxY}.
+Place all new nodes OUTSIDE this bounding box — below (y > {maxY} + 100) or to the right (x > {maxX} + 100).
+You may create edges that connect new nodes to existing nodes if the description implies a connection.
+Use these existing node IDs for connections: {existing_node_ids}"""
+
+
+async def generate_diagram(
+    request: AIGenerateRequest,
+    available_slugs: list[str],
+    existing_node_ids: list[str] | None = None,
+) -> AIGenerateResponse:
+    merge_instructions = ""
+    if request.mode == "merge" and request.existingBounds:
+        b = request.existingBounds
+        merge_instructions = MERGE_INSTRUCTIONS.format(
+            minX=b.minX, maxX=b.maxX, minY=b.minY, maxY=b.maxY,
+            existing_node_ids=", ".join(existing_node_ids or []),
+        )
+
+    system_prompt = SYSTEM_PROMPT_TEMPLATE.format(
+        available_slugs=", ".join(available_slugs),
+        merge_instructions=merge_instructions,
+    )
+
+    model = settings.get_model_for_action("network_diagram_generate")
+    provider = get_ai_provider(model)
+
+    messages = [{"role": "user", "content": request.description}]
+
+    response_text, input_tokens, output_tokens = await provider.generate_json(
+        system_prompt=system_prompt,
+        messages=messages,
+        max_tokens=4096,
+    )
+
+    logger.info(
+        "Network diagram AI generation: input_tokens=%d, output_tokens=%d",
+        input_tokens, output_tokens,
+    )
+
+    try:
+        data = json.loads(response_text)
+    except json.JSONDecodeError as e:
+        logger.error("Failed to parse AI response as JSON: %s", e)
+        raise ValueError("AI generated an invalid response, please try again")
+
+    nodes = []
+    for raw_node in data.get("nodes", []):
+        node_type = raw_node.get("type", "server")
+        if node_type not in available_slugs:
+            logger.warning("Unknown device type '%s', falling back to 'server'", node_type)
+            node_type = "server"
+
+        nodes.append(DiagramNode(
+            id=raw_node["id"],
+            type=node_type,
+            label=raw_node.get("label", node_type),
+            position=raw_node.get("position", {"x": 0, "y": 0}),
+            properties=DeviceProperties(**{
+                k: v for k, v in raw_node.get("properties", {}).items()
+                if k in DeviceProperties.model_fields
+            }),
+        ))
+
+    edges = []
+    for raw_edge in data.get("edges", []):
+        edges.append(DiagramEdge(
+            id=raw_edge["id"],
+            source=raw_edge["source"],
+            target=raw_edge["target"],
+            label=raw_edge.get("label"),
+            connectionType=raw_edge.get("connectionType", "ethernet"),
+            speed=raw_edge.get("speed"),
+            notes=raw_edge.get("notes"),
+        ))
+
+    return AIGenerateResponse(
+        nodes=nodes,
+        edges=edges,
+        suggestedName=data.get("suggestedName"),
+        notes=data.get("notes"),
+    )