feat(m2): variant coverage — all 5 LGB objectives, importance, trees view (#5)

Author: dgtalbug

.gitignore

@@ -25,6 +25,8 @@ claude.md
 # Runtime data: artifacts (source of truth) + derived SQLite registry + logs
 /data/
 *.cerebro.json
+# Committed example artifacts are the snapshot test fixtures — keep them
+!examples/*.cerebro.json
 *.db
 *.db-wal
 *.db-shm

contracts/openapi/openapi.json

@@ -19,6 +19,18 @@
           "model": {
             "$ref": "#/components/schemas/Model"
           },
+          "rank_metadata": {
+            "anyOf": [
+              {
+                "additionalProperties": true,
+                "type": "object"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Rank Metadata"
+          },
           "schema_version": {
             "const": "1.0.0",
             "title": "Schema Version",
@@ -120,8 +132,35 @@
       },
       "Importance": {
         "additionalProperties": false,
-        "description": "Feature importance scores keyed by feature name.\n\n`permutation` is locked to None in v1.0.0. When permutation importance\nlands, it will use the shape `{feature_name: {\"mean\": float, \"std\": float}}`\nbehind a schema-version bump.",
+        "description": "Feature importance scores keyed by feature name.",
         "properties": {
+          "divergence_warnings": {
+            "anyOf": [
+              {
+                "items": {
+                  "additionalProperties": {
+                    "anyOf": [
+                      {
+                        "type": "string"
+                      },
+                      {
+                        "type": "integer"
+                      },
+                      {
+                        "type": "number"
+                      }
+                    ]
+                  },
+                  "type": "object"
+                },
+                "type": "array"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Divergence Warnings"
+          },
           "gain": {
             "additionalProperties": {
               "type": "number"
@@ -169,7 +208,6 @@
             "$ref": "#/components/schemas/FeatureSchema"
           },
           "num_class": {
-            "const": 1,
             "title": "Num Class",
             "type": "integer"
           },
@@ -178,7 +216,13 @@
             "type": "integer"
           },
           "objective": {
-            "const": "binary",
+            "enum": [
+              "binary",
+              "multiclass",
+              "regression",
+              "lambdarank",
+              "multi_output"
+            ],
             "title": "Objective",
             "type": "string"
           },
@@ -439,6 +483,62 @@
         ]
       }
     },
+    "/artifacts/{artifact_id}/importance": {
+      "get": {
+        "description": "Return importance scores for the requested type.\n\n- gain / split: always available (computed at extraction time).\n- permutation: available only when evaluation samples were provided\n  at extraction time; returns HTTP 200 with empty features list and a\n  detail message when absent.",
+        "operationId": "get_importance_artifacts__artifact_id__importance_get",
+        "parameters": [
+          {
+            "in": "path",
+            "name": "artifact_id",
+            "required": true,
+            "schema": {
+              "title": "Artifact Id",
+              "type": "string"
+            }
+          },
+          {
+            "description": "Importance type: gain, split, or permutation",
+            "in": "query",
+            "name": "type",
+            "required": true,
+            "schema": {
+              "description": "Importance type: gain, split, or permutation",
+              "title": "Type",
+              "type": "string"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "content": {
+              "application/json": {
+                "schema": {
+                  "additionalProperties": true,
+                  "title": "Response Get Importance Artifacts  Artifact Id  Importance Get",
+                  "type": "object"
+                }
+              }
+            },
+            "description": "Successful Response"
+          },
+          "422": {
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/HTTPValidationError"
+                }
+              }
+            },
+            "description": "Validation Error"
+          }
+        },
+        "summary": "Get Importance",
+        "tags": [
+          "artifacts"
+        ]
+      }
+    },
     "/health": {
       "get": {
         "description": "Liveness probe \u2014 does not check storage or downstream deps.",