fix: set preferred transport on agent cards (#1689)

## Summary
- set `PreferredTransport` to `JSONRPC` when the controller builds A2A
agent cards
- add regression coverage for `GetA2AAgentCard` so controller-generated
cards keep that field populated
- keep the change limited to the translator path described in #1684

## Testing
- `/opt/homebrew/bin/go test ./core/internal/controller/translator/agent
-run TestGetA2AAgentCard`

Fixes #1684

---------

Signed-off-by: Gnani Rahul <gnutakki@radiantlogic.com>
Co-authored-by: Eitan Yarmush <eitan.yarmush@solo.io>

Author: gnanirahulnutakki

go/core/internal/controller/translator/agent/testdata/outputs/agent_with_allowed_headers.json

@@ -13,6 +13,7 @@
     ],
     "description": "",
     "name": "agent",
+    "preferredTransport": "JSONRPC",
     "skills": null,
     "url": "http://agent.test:8080",
     "version": ""
@@ -69,7 +70,7 @@
         ]
       },
       "stringData": {
-        "agent-card.json": "{\"name\":\"agent\",\"description\":\"\",\"url\":\"http://agent.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[]}",
+        "agent-card.json": "{\"name\":\"agent\",\"description\":\"\",\"url\":\"http://agent.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[],\"preferredTransport\":\"JSONRPC\"}",
         "config.json": "{\"model\":{\"type\":\"openai\",\"model\":\"gpt-4o\",\"base_url\":\"\"},\"description\":\"\",\"instruction\":\"You are a helpful assistant.\",\"http_tools\":[{\"params\":{\"url\":\"http://mcp-server.test:8080/mcp\",\"headers\":{}},\"tools\":[\"tool1\",\"tool2\"],\"allowed_headers\":[\"x-user-email\",\"x-tenant-id\"]}],\"stream\":false}"
       }
     },
@@ -139,7 +140,7 @@
         "template": {
           "metadata": {
             "annotations": {
-              "kagent.dev/config-hash": "3163633853400579791"
+              "kagent.dev/config-hash": "5387783918115122395"
             },
             "labels": {
               "app": "kagent",

go/core/internal/controller/translator/agent/testdata/outputs/agent_with_code.json

@@ -13,6 +13,7 @@
     ],
     "description": "",
     "name": "agent_with_code",
+    "preferredTransport": "JSONRPC",
     "skills": null,
     "url": "http://agent-with-code.test:8080",
     "version": ""
@@ -61,7 +62,7 @@
         ]
       },
       "stringData": {
-        "agent-card.json": "{\"name\":\"agent_with_code\",\"description\":\"\",\"url\":\"http://agent-with-code.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[]}",
+        "agent-card.json": "{\"name\":\"agent_with_code\",\"description\":\"\",\"url\":\"http://agent-with-code.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[],\"preferredTransport\":\"JSONRPC\"}",
         "config.json": "{\"model\":{\"type\":\"openai\",\"model\":\"gpt-4o\",\"headers\":{\"User-Agent\":\"kagent/1.0\"},\"base_url\":\"\",\"max_tokens\":1024,\"reasoning_effort\":\"low\",\"temperature\":0.7,\"top_p\":0.95},\"description\":\"\",\"instruction\":\"You are a helpful assistant.\",\"execute_code\":true,\"stream\":false}",
         "srt-settings.json": "{\"filesystem\":{\"allowWrite\":[\".\",\"/tmp\"],\"denyRead\":[],\"denyWrite\":[]},\"network\":{\"allowedDomains\":[],\"deniedDomains\":[]}}"
       }
@@ -132,7 +133,7 @@
         "template": {
           "metadata": {
             "annotations": {
-              "kagent.dev/config-hash": "3112549247443018156"
+              "kagent.dev/config-hash": "17724008177186270332"
             },
             "labels": {
               "app": "kagent",

go/core/internal/controller/translator/agent/testdata/outputs/agent_with_context_config.json

@@ -13,6 +13,7 @@
     ],
     "description": "Agent with context management",
     "name": "agent_with_context",
+    "preferredTransport": "JSONRPC",
     "skills": null,
     "url": "http://agent-with-context.test:8080",
     "version": ""
@@ -71,7 +72,7 @@
         ]
       },
       "stringData": {
-        "agent-card.json": "{\"name\":\"agent_with_context\",\"description\":\"Agent with context management\",\"url\":\"http://agent-with-context.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[]}",
+        "agent-card.json": "{\"name\":\"agent_with_context\",\"description\":\"Agent with context management\",\"url\":\"http://agent-with-context.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[],\"preferredTransport\":\"JSONRPC\"}",
         "config.json": "{\"model\":{\"type\":\"openai\",\"model\":\"gpt-4o\",\"headers\":{\"User-Agent\":\"kagent/1.0\"},\"base_url\":\"\",\"max_tokens\":1024,\"temperature\":0.7},\"description\":\"Agent with context management\",\"instruction\":\"You are a helpful assistant with context management enabled.\",\"stream\":false,\"context_config\":{\"compaction\":{\"compaction_interval\":5,\"overlap_size\":2,\"summarizer_model\":{\"type\":\"anthropic\",\"model\":\"claude-3-haiku\"},\"prompt_template\":\"Summarize the following conversation events concisely.\",\"token_threshold\":50000,\"event_retention_size\":10}}}"
       }
     },
@@ -141,7 +142,7 @@
         "template": {
           "metadata": {
             "annotations": {
-              "kagent.dev/config-hash": "542503096430191840"
+              "kagent.dev/config-hash": "16891892632874106599"
             },
             "labels": {
               "app": "kagent",

go/core/internal/controller/translator/agent/testdata/outputs/agent_with_cross_namespace_tools.json

@@ -13,6 +13,7 @@
     ],
     "description": "An agent that uses cross-namespace tools",
     "name": "source_agent",
+    "preferredTransport": "JSONRPC",
     "skills": null,
     "url": "http://source-agent.source-ns:8080",
     "version": ""
@@ -75,7 +76,7 @@
         ]
       },
       "stringData": {
-        "agent-card.json": "{\"name\":\"source_agent\",\"description\":\"An agent that uses cross-namespace tools\",\"url\":\"http://source-agent.source-ns:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[]}",
+        "agent-card.json": "{\"name\":\"source_agent\",\"description\":\"An agent that uses cross-namespace tools\",\"url\":\"http://source-agent.source-ns:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[],\"preferredTransport\":\"JSONRPC\"}",
         "config.json": "{\"model\":{\"type\":\"openai\",\"model\":\"gpt-4o\",\"base_url\":\"\"},\"description\":\"An agent that uses cross-namespace tools\",\"instruction\":\"You are an assistant with access to shared tools.\",\"http_tools\":[{\"params\":{\"url\":\"http://tools.tools-ns.svc:8080/mcp\",\"headers\":{\"Authorization\":\"tool-secret-token\"},\"timeout\":30},\"tools\":[\"list_resources\",\"get_resource\"]}],\"remote_agents\":[{\"name\":\"tools_ns__NS__tools_agent\",\"url\":\"http://tools-agent.tools-ns:8080\",\"description\":\"An agent that can be used as a cross-namespace tool\"}],\"stream\":false}"
       }
     },
@@ -145,7 +146,7 @@
         "template": {
           "metadata": {
             "annotations": {
-              "kagent.dev/config-hash": "4884557913361845254"
+              "kagent.dev/config-hash": "6527476808794662414"
             },
             "labels": {
               "app": "kagent",

go/core/internal/controller/translator/agent/testdata/outputs/agent_with_custom_sa.json

@@ -13,6 +13,7 @@
     ],
     "description": "",
     "name": "agent_with_custom_sa",
+    "preferredTransport": "JSONRPC",
     "skills": null,
     "url": "http://agent-with-custom-sa.test:8080",
     "version": ""
@@ -53,7 +54,7 @@
         ]
       },
       "stringData": {
-        "agent-card.json": "{\"name\":\"agent_with_custom_sa\",\"description\":\"\",\"url\":\"http://agent-with-custom-sa.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[]}",
+        "agent-card.json": "{\"name\":\"agent_with_custom_sa\",\"description\":\"\",\"url\":\"http://agent-with-custom-sa.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[],\"preferredTransport\":\"JSONRPC\"}",
         "config.json": "{\"model\":{\"type\":\"openai\",\"model\":\"gpt-4\",\"base_url\":\"\"},\"description\":\"\",\"instruction\":\"You are a helpful assistant.\",\"stream\":false}"
       }
     },
@@ -98,7 +99,7 @@
         "template": {
           "metadata": {
             "annotations": {
-              "kagent.dev/config-hash": "10888184615299925090"
+              "kagent.dev/config-hash": "13887560842969010876"
             },
             "labels": {
               "app": "kagent",

go/core/internal/controller/translator/agent/testdata/outputs/agent_with_default_sa.json

@@ -13,6 +13,7 @@
     ],
     "description": "",
     "name": "agent_with_default_sa",
+    "preferredTransport": "JSONRPC",
     "skills": null,
     "url": "http://agent-with-default-sa.test:8080",
     "version": ""
@@ -53,7 +54,7 @@
         ]
       },
       "stringData": {
-        "agent-card.json": "{\"name\":\"agent_with_default_sa\",\"description\":\"\",\"url\":\"http://agent-with-default-sa.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[]}",
+        "agent-card.json": "{\"name\":\"agent_with_default_sa\",\"description\":\"\",\"url\":\"http://agent-with-default-sa.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[],\"preferredTransport\":\"JSONRPC\"}",
         "config.json": "{\"model\":{\"type\":\"openai\",\"model\":\"gpt-4\",\"base_url\":\"\"},\"description\":\"\",\"instruction\":\"You are a helpful assistant.\",\"stream\":false}"
       }
     },
@@ -98,7 +99,7 @@
         "template": {
           "metadata": {
             "annotations": {
-              "kagent.dev/config-hash": "9686053632527538314"
+              "kagent.dev/config-hash": "8931708887213057908"
             },
             "labels": {
               "app": "kagent",

go/core/internal/controller/translator/agent/testdata/outputs/agent_with_embedding_provider.json

@@ -13,6 +13,7 @@
     ],
     "description": "",
     "name": "agent_cross_provider_memory",
+    "preferredTransport": "JSONRPC",
     "skills": null,
     "url": "http://agent-cross-provider-memory.test:8080",
     "version": ""
@@ -59,7 +60,7 @@
         ]
       },
       "stringData": {
-        "agent-card.json": "{\"name\":\"agent_cross_provider_memory\",\"description\":\"\",\"url\":\"http://agent-cross-provider-memory.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[]}",
+        "agent-card.json": "{\"name\":\"agent_cross_provider_memory\",\"description\":\"\",\"url\":\"http://agent-cross-provider-memory.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[],\"preferredTransport\":\"JSONRPC\"}",
         "config.json": "{\"model\":{\"type\":\"openai\",\"model\":\"gpt-4o\",\"base_url\":\"\"},\"description\":\"\",\"instruction\":\"You are an assistant.\",\"stream\":false,\"memory\":{\"embedding\":{\"provider\":\"gemini_vertex_ai\",\"model\":\"text-embedding-005\"}}}"
       }
     },
@@ -129,7 +130,7 @@
         "template": {
           "metadata": {
             "annotations": {
-              "kagent.dev/config-hash": "13646724703108583778"
+              "kagent.dev/config-hash": "10448813021284432574"
             },
             "labels": {
               "app": "kagent",

go/core/internal/controller/translator/agent/testdata/outputs/agent_with_git_skills.json

@@ -13,6 +13,7 @@
     ],
     "description": "",
     "name": "git_skills_agent",
+    "preferredTransport": "JSONRPC",
     "skills": null,
     "url": "http://git-skills-agent.test:8080",
     "version": ""
@@ -60,7 +61,7 @@
         ]
       },
       "stringData": {
-        "agent-card.json": "{\"name\":\"git_skills_agent\",\"description\":\"\",\"url\":\"http://git-skills-agent.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[]}",
+        "agent-card.json": "{\"name\":\"git_skills_agent\",\"description\":\"\",\"url\":\"http://git-skills-agent.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[],\"preferredTransport\":\"JSONRPC\"}",
         "config.json": "{\"model\":{\"type\":\"openai\",\"model\":\"gpt-4o\",\"headers\":{\"User-Agent\":\"kagent/1.0\"},\"base_url\":\"\",\"max_tokens\":1024,\"reasoning_effort\":\"low\",\"temperature\":0.7,\"top_p\":0.95},\"description\":\"\",\"instruction\":\"You are a helpful assistant with skills from git.\",\"stream\":false}",
         "srt-settings.json": "{\"filesystem\":{\"allowWrite\":[\".\",\"/tmp\"],\"denyRead\":[],\"denyWrite\":[]},\"network\":{\"allowedDomains\":[],\"deniedDomains\":[]}}"
       }
@@ -131,7 +132,7 @@
         "template": {
           "metadata": {
             "annotations": {
-              "kagent.dev/config-hash": "10549266842660390977"
+              "kagent.dev/config-hash": "9443054578640766875"
             },
             "labels": {
               "app": "kagent",

go/core/internal/controller/translator/agent/testdata/outputs/agent_with_http_toolserver.json

@@ -13,6 +13,7 @@
     ],
     "description": "",
     "name": "agent",
+    "preferredTransport": "JSONRPC",
     "skills": null,
     "url": "http://agent.test:8080",
     "version": ""
@@ -68,7 +69,7 @@
         ]
       },
       "stringData": {
-        "agent-card.json": "{\"name\":\"agent\",\"description\":\"\",\"url\":\"http://agent.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[]}",
+        "agent-card.json": "{\"name\":\"agent\",\"description\":\"\",\"url\":\"http://agent.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[],\"preferredTransport\":\"JSONRPC\"}",
         "config.json": "{\"model\":{\"type\":\"openai\",\"model\":\"gpt-4o\",\"base_url\":\"\"},\"description\":\"\",\"instruction\":\"You are a math toolserver. Focus on solving mathematical problems step by step.\",\"http_tools\":[{\"params\":{\"url\":\"http://localhost:8084/mcp\",\"headers\":{\"MATH\":\"sk-test-api-key\"},\"timeout\":30,\"sse_read_timeout\":300},\"tools\":[\"k8s_get_resources\"]}],\"stream\":false}"
       }
     },
@@ -138,7 +139,7 @@
         "template": {
           "metadata": {
             "annotations": {
-              "kagent.dev/config-hash": "5747732709328998873"
+              "kagent.dev/config-hash": "4534869863837852487"
             },
             "labels": {
               "app": "kagent",

go/core/internal/controller/translator/agent/testdata/outputs/agent_with_mcp_service.json

@@ -13,6 +13,7 @@
     ],
     "description": "",
     "name": "agent",
+    "preferredTransport": "JSONRPC",
     "skills": null,
     "url": "http://agent.test:8080",
     "version": ""
@@ -64,7 +65,7 @@
         ]
       },
       "stringData": {
-        "agent-card.json": "{\"name\":\"agent\",\"description\":\"\",\"url\":\"http://agent.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[]}",
+        "agent-card.json": "{\"name\":\"agent\",\"description\":\"\",\"url\":\"http://agent.test:8080\",\"version\":\"\",\"capabilities\":{\"streaming\":true,\"pushNotifications\":false,\"stateTransitionHistory\":true},\"defaultInputModes\":[\"text\"],\"defaultOutputModes\":[\"text\"],\"skills\":[],\"preferredTransport\":\"JSONRPC\"}",
         "config.json": "{\"model\":{\"type\":\"openai\",\"model\":\"gpt-4o\",\"base_url\":\"\"},\"description\":\"\",\"instruction\":\"You are a math toolserver. Focus on solving mathematical problems step by step.\",\"http_tools\":[{\"params\":{\"url\":\"http://toolserver.test:8084/mcp\",\"headers\":{}},\"tools\":[\"k8s_get_resources\"]}],\"stream\":false}"
       }
     },
@@ -134,7 +135,7 @@
         "template": {
           "metadata": {
             "annotations": {
-              "kagent.dev/config-hash": "16446945615890817909"
+              "kagent.dev/config-hash": "12595169530626754046"
             },
             "labels": {
               "app": "kagent",