From 717c88aaece00036a6d8e28d8bb889ce3a4ad2a4 Mon Sep 17 00:00:00 2001
From: Charles <azanux@gmail.com>
Date: Sat, 7 Feb 2026 20:56:44 +0100
Subject: [PATCH] fix:Wrap non-JSON tool responses for Gemini compatibility

Signed-off-by: Charles <azanux@gmail.com>
---
 .../embabel/agent/api/tool/MatryoshkaTool.kt  | 20 +++++--
 .../spi/support/springai/messageConverters.kt | 16 +++++-
 .../agent/spi/loop/MatryoshkaToolTest.kt      | 35 ++++++------
 .../support/springai/MessageConversionTest.kt | 56 +++++++++++++++++++
 4 files changed, 103 insertions(+), 24 deletions(-)

diff --git a/embabel-agent-api/src/main/kotlin/com/embabel/agent/api/tool/MatryoshkaTool.kt b/embabel-agent-api/src/main/kotlin/com/embabel/agent/api/tool/MatryoshkaTool.kt
index 0915f42d3..ffac43ab1 100644
--- a/embabel-agent-api/src/main/kotlin/com/embabel/agent/api/tool/MatryoshkaTool.kt
+++ b/embabel-agent-api/src/main/kotlin/com/embabel/agent/api/tool/MatryoshkaTool.kt
@@ -559,6 +559,18 @@ interface MatryoshkaTool : Tool {
     }
 }
 
+/**
+ * Returns a JSON-formatted tool response listing enabled tools.
+ * JSON format ensures compatibility with LLM providers that require
+ * valid JSON in tool responses (e.g. Google Gemini).
+ */
+private fun enabledToolsJson(toolNames: List<String>): Tool.Result {
+    val toolNamesJson = toolNames.joinToString(", ") { "\"$it\"" }
+    return Tool.Result.text(
+        """{"enabled_tools_count": ${toolNames.size}, "enabled_tools": [$toolNamesJson]}"""
+    )
+}
+
 /**
  * Simple implementation that exposes all inner tools.
  */
@@ -571,9 +583,7 @@ private class SimpleMatryoshkaTool(
 
     override fun call(input: String): Tool.Result {
         val toolNames = innerTools.map { it.definition.name }
-        return Tool.Result.text(
-            "Enabled ${innerTools.size} tools: ${toolNames.joinToString(", ")}"
-        )
+        return enabledToolsJson(toolNames)
     }
 }
 
@@ -593,8 +603,6 @@ private class SelectableMatryoshkaTool(
     override fun call(input: String): Tool.Result {
         val selected = selectTools(input)
         val toolNames = selected.map { it.definition.name }
-        return Tool.Result.text(
-            "Enabled ${selected.size} tools: ${toolNames.joinToString(", ")}"
-        )
+        return enabledToolsJson(toolNames)
     }
 }
diff --git a/embabel-agent-api/src/main/kotlin/com/embabel/agent/spi/support/springai/messageConverters.kt b/embabel-agent-api/src/main/kotlin/com/embabel/agent/spi/support/springai/messageConverters.kt
index 5d2f84f9f..c7f732d7b 100644
--- a/embabel-agent-api/src/main/kotlin/com/embabel/agent/spi/support/springai/messageConverters.kt
+++ b/embabel-agent-api/src/main/kotlin/com/embabel/agent/spi/support/springai/messageConverters.kt
@@ -16,6 +16,7 @@
 package com.embabel.agent.spi.support.springai
 
 import com.embabel.chat.*
+import com.fasterxml.jackson.databind.ObjectMapper
 import org.springframework.ai.content.Media
 import org.springframework.core.io.ByteArrayResource
 import org.springframework.util.MimeTypeUtils
@@ -50,7 +51,7 @@ fun Message.toSpringAiMessage(): SpringAiMessage {
             val toolResponse = ToolResponseMessage.ToolResponse(
                 this.toolCallId,
                 this.toolName,
-                this.textContent
+                this.textContent.ensureJson()
             )
             ToolResponseMessage.builder().responses(listOf(toolResponse)).metadata(metadata).build()
         }
@@ -123,6 +124,19 @@ internal fun List<SpringAiMessage>.mergeConsecutiveToolResponses(): List<SpringA
  * Convert a Spring AI AssistantMessage to an Embabel message.
  * Handles both regular messages and messages with tool calls.
  */
+/**
+ * Ensures the string is valid JSON for Gemini compatibility.
+ * The Google GenAI adapter parses tool response data as JSON.
+ * Plain text responses must be wrapped in a JSON object.
+ */
+private fun String.ensureJson(): String {
+    val trimmed = trimStart()
+    if (trimmed.startsWith('{') || trimmed.startsWith('[')) {
+        return this
+    }
+    return ObjectMapper().writeValueAsString(mapOf("result" to this))
+}
+
 fun SpringAiAssistantMessage.toEmbabelMessage(): Message {
     val toolCalls = this.toolCalls
     return if (toolCalls.isNullOrEmpty()) {
diff --git a/embabel-agent-api/src/test/kotlin/com/embabel/agent/spi/loop/MatryoshkaToolTest.kt b/embabel-agent-api/src/test/kotlin/com/embabel/agent/spi/loop/MatryoshkaToolTest.kt
index 3fc02aee7..ce2ba4f01 100644
--- a/embabel-agent-api/src/test/kotlin/com/embabel/agent/spi/loop/MatryoshkaToolTest.kt
+++ b/embabel-agent-api/src/test/kotlin/com/embabel/agent/spi/loop/MatryoshkaToolTest.kt
@@ -64,7 +64,7 @@ class MatryoshkaToolTest {
         }
 
         @Test
-        fun `call returns message listing enabled tools`() {
+        fun `call returns JSON message listing enabled tools`() {
             val innerTool1 = MockTool("tool_a", "Tool A") { Tool.Result.text("a") }
             val innerTool2 = MockTool("tool_b", "Tool B") { Tool.Result.text("b") }
 
@@ -78,9 +78,10 @@ class MatryoshkaToolTest {
 
             assertTrue(result is Tool.Result.Text)
             val text = (result as Tool.Result.Text).content
-            assertTrue(text.contains("2 tools"))
-            assertTrue(text.contains("tool_a"))
-            assertTrue(text.contains("tool_b"))
+            val json = objectMapper.readTree(text)
+            assertEquals(2, json["enabled_tools_count"].intValue())
+            val toolNames = json["enabled_tools"].map { it.textValue() }
+            assertEquals(listOf("tool_a", "tool_b"), toolNames)
         }
 
         @Test
@@ -282,7 +283,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "outer",
                     toolInput = "{}",
-                    result = "Enabled 1 tools: inner",
+                    result = """{"enabled_tools_count": 1, "enabled_tools": ["inner"]}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -316,7 +317,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "persistent",
                     toolInput = "{}",
-                    result = "Enabled 1 tools: inner",
+                    result = """{"enabled_tools_count": 1, "enabled_tools": ["inner"]}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -353,7 +354,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "selector",
                     toolInput = """{"pick": "one"}""",
-                    result = "Enabled 1 tools: tool1",
+                    result = """{"enabled_tools_count": 1, "enabled_tools": ["tool1"]}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -383,7 +384,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "empty",
                     toolInput = "{}",
-                    result = "Enabled 0 tools:",
+                    result = """{"enabled_tools_count": 0, "enabled_tools": []}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -413,7 +414,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "composer_stats",
                     toolInput = "{}",
-                    result = "Enabled 2 tools: count, getValues",
+                    result = """{"enabled_tools_count": 2, "enabled_tools": ["count", "getValues"]}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -445,7 +446,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "composer_stats",
                     toolInput = "{}",
-                    result = "Enabled 2 tools: count, getValues",
+                    result = """{"enabled_tools_count": 2, "enabled_tools": ["count", "getValues"]}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -481,7 +482,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "composer_stats",
                     toolInput = "{}",
-                    result = "Enabled 2 tools: count, getValues",
+                    result = """{"enabled_tools_count": 2, "enabled_tools": ["count", "getValues"]}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -520,7 +521,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "empty",
                     toolInput = "{}",
-                    result = "Enabled 0 tools:",
+                    result = """{"enabled_tools_count": 0, "enabled_tools": []}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -550,7 +551,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "spotify_search",
                     toolInput = "{}",
-                    result = "Enabled 2 tools: vector_search, text_search",
+                    result = """{"enabled_tools_count": 2, "enabled_tools": ["vector_search", "text_search"]}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -588,7 +589,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "music_search",
                     toolInput = "{}",
-                    result = "Enabled 2 tools",
+                    result = """{"enabled_tools_count": 2, "enabled_tools": ["vector_search", "text_search"]}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -625,7 +626,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "no_notes",
                     toolInput = "{}",
-                    result = "Enabled 1 tool",
+                    result = """{"enabled_tools_count": 1, "enabled_tools": ["tool1"]}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -695,7 +696,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "outer",
                     toolInput = "{}",
-                    result = "Enabled 1 tools: inner",
+                    result = """{"enabled_tools_count": 1, "enabled_tools": ["inner"]}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
@@ -936,7 +937,7 @@ class MatryoshkaToolTest {
                 lastToolCall = ToolCallResult(
                     toolName = "music_search",
                     toolInput = "{}",
-                    result = "Enabled 2 tools",
+                    result = """{"enabled_tools_count": 2, "enabled_tools": ["vectorSearch", "textSearch"]}""",
                     resultObject = null,
                 ),
                 iterationCount = 1,
diff --git a/embabel-agent-api/src/test/kotlin/com/embabel/agent/spi/support/springai/MessageConversionTest.kt b/embabel-agent-api/src/test/kotlin/com/embabel/agent/spi/support/springai/MessageConversionTest.kt
index ff5e5cef4..b92058214 100644
--- a/embabel-agent-api/src/test/kotlin/com/embabel/agent/spi/support/springai/MessageConversionTest.kt
+++ b/embabel-agent-api/src/test/kotlin/com/embabel/agent/spi/support/springai/MessageConversionTest.kt
@@ -209,6 +209,62 @@ class MessageConversionTest {
             assertThat(response.name()).isEqualTo("get_weather")
             assertThat(response.responseData()).isEqualTo("""{"temperature": 72}""")
         }
+
+        @Test
+        fun `tool result with plain text content is wrapped as JSON`() {
+            val message = ToolResultMessage(
+                toolCallId = "call-1",
+                toolName = "search",
+                content = "2 results: HBNB Services - Technical Blockchain Advisor"
+            )
+
+            val springAiMessage = message.toSpringAiMessage() as ToolResponseMessage
+            val responseData = springAiMessage.responses[0].responseData()
+
+            assertThat(responseData).startsWith("{")
+            assertThat(responseData).contains("\"result\"")
+            assertThat(responseData).contains("2 results: HBNB Services - Technical Blockchain Advisor")
+        }
+
+        @Test
+        fun `tool result with valid JSON object content is preserved`() {
+            val message = ToolResultMessage(
+                toolCallId = "call-1",
+                toolName = "get_count",
+                content = """{"count": 5}"""
+            )
+
+            val springAiMessage = message.toSpringAiMessage() as ToolResponseMessage
+
+            assertThat(springAiMessage.responses[0].responseData()).isEqualTo("""{"count": 5}""")
+        }
+
+        @Test
+        fun `tool result with valid JSON array content is preserved`() {
+            val message = ToolResultMessage(
+                toolCallId = "call-1",
+                toolName = "get_items",
+                content = """[1, 2, 3]"""
+            )
+
+            val springAiMessage = message.toSpringAiMessage() as ToolResponseMessage
+
+            assertThat(springAiMessage.responses[0].responseData()).isEqualTo("""[1, 2, 3]""")
+        }
+
+        @Test
+        fun `tool result with whitespace-only content is wrapped as JSON`() {
+            val message = ToolResultMessage(
+                toolCallId = "call-1",
+                toolName = "no_result",
+                content = " "
+            )
+
+            val springAiMessage = message.toSpringAiMessage() as ToolResponseMessage
+            val responseData = springAiMessage.responses[0].responseData()
+
+            assertThat(responseData).isEqualTo("""{"result":" "}""")
+        }
     }
 
     @Nested