feat: add memory citation to agent message (#14821)

Client side to come

codex-rs/app-server-protocol/schema/json/v2/TurnStartResponse.json

@@ -403,6 +403,54 @@
       ],
       "type": "string"
     },
+    "MemoryCitation": {
+      "properties": {
+        "entries": {
+          "items": {
+            "$ref": "#/definitions/MemoryCitationEntry"
+          },
+          "type": "array"
+        },
+        "threadIds": {
+          "items": {
+            "type": "string"
+          },
+          "type": "array"
+        }
+      },
+      "required": [
+        "entries",
+        "threadIds"
+      ],
+      "type": "object"
+    },
+    "MemoryCitationEntry": {
+      "properties": {
+        "lineEnd": {
+          "format": "uint32",
+          "minimum": 0.0,
+          "type": "integer"
+        },
+        "lineStart": {
+          "format": "uint32",
+          "minimum": 0.0,
+          "type": "integer"
+        },
+        "note": {
+          "type": "string"
+        },
+        "path": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "lineEnd",
+        "lineStart",
+        "note",
+        "path"
+      ],
+      "type": "object"
+    },
     "MessagePhase": {
       "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
@@ -558,6 +606,17 @@
             "id": {
               "type": "string"
             },
+            "memoryCitation": {
+              "anyOf": [
+                {
+                  "$ref": "#/definitions/MemoryCitation"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "default": null
+            },
             "phase": {
               "anyOf": [
                 {