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fix: Wrap non-JSON tool responses for Gemini compatibility #1392

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fix: Wrap non-JSON tool responses for Gemini compatibility #1392

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717c88a
fix:Wrap non-JSON tool responses for Gemini compatibility
azanux Feb 7, 2026
0407e13
Merge remote-tracking branch 'origin/main' into fix/matryoshka-tool-j…
azanux Feb 8, 2026
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20 changes: 14 additions & 6 deletions embabel-agent-api/src/main/kotlin/com/embabel/agent/api/tool/MatryoshkaTool.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -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.
*/
Expand All @@ -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)
}
}

Expand All @@ -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)
}
}
16 changes: 15 additions & 1 deletion ...bel-agent-api/src/main/kotlin/com/embabel/agent/spi/support/springai/messageConverters.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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()
}
Expand Down Expand Up @@ -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()) {
Expand Down
35 changes: 18 additions & 17 deletions embabel-agent-api/src/test/kotlin/com/embabel/agent/spi/loop/MatryoshkaToolTest.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -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") }

Expand All @@ -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
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down
56 changes: 56 additions & 0 deletions ...agent-api/src/test/kotlin/com/embabel/agent/spi/support/springai/MessageConversionTest.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down