Improve thinking/tool signature handling for Claude and Gemini requests

Prefer cached signatures and avoid injecting dummy thinking blocks; instead remove unsigned thinking blocks and add a skip sentinel for tool calls without a valid signature. Generate stable session IDs from the first user message, apply schema cleaning only for Claude models, and reorder thinking parts so thinking appears first. For Gemini, remove thinking blocks and attach a skip sentinel to function calls. Simplify response handling by passing raw function args through (remove special Bash conversion). Update and add tests to reflect the new behavior.

These changes prevent rejected dummy signatures, improve compatibility with Antigravity’s signature validation, provide more stable session IDs for conversation grouping, and make request/response translation more robust.

internal/translator/antigravity/claude/antigravity_claude_request_test.go

@@ -105,6 +105,7 @@ func TestConvertClaudeRequestToAntigravity_ThinkingBlocks(t *testing.T) {
 }
 
 func TestConvertClaudeRequestToAntigravity_ThinkingBlockWithoutSignature(t *testing.T) {
+	// Unsigned thinking blocks should be removed entirely (not converted to text)
 	inputJSON := []byte(`{
 		"model": "claude-sonnet-4-5-thinking",
 		"messages": [
@@ -121,11 +122,18 @@ func TestConvertClaudeRequestToAntigravity_ThinkingBlockWithoutSignature(t *test
 	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5-thinking", inputJSON, false)
 	outputStr := string(output)
 
-	// Without signature, should use sentinel value
-	firstPart := gjson.Get(outputStr, "request.contents.0.parts.0")
-	if firstPart.Get("thoughtSignature").String() != geminiCLIClaudeThoughtSignature {
-		t.Errorf("Expected sentinel signature '%s', got '%s'",
-			geminiCLIClaudeThoughtSignature, firstPart.Get("thoughtSignature").String())
+	// Without signature, thinking block should be removed (not converted to text)
+	parts := gjson.Get(outputStr, "request.contents.0.parts").Array()
+	if len(parts) != 1 {
+		t.Fatalf("Expected 1 part (thinking removed), got %d", len(parts))
+	}
+
+	// Only text part should remain
+	if parts[0].Get("thought").Bool() {
+		t.Error("Thinking block should be removed, not preserved")
+	}
+	if parts[0].Get("text").String() != "Answer" {
+		t.Errorf("Expected text 'Answer', got '%s'", parts[0].Get("text").String())
 	}
 }
 
@@ -192,10 +200,16 @@ func TestConvertClaudeRequestToAntigravity_ToolUse(t *testing.T) {
 	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5", inputJSON, false)
 	outputStr := string(output)
 
-	// Check function call conversion
-	funcCall := gjson.Get(outputStr, "request.contents.0.parts.0.functionCall")
+	// Now we expect only 1 part (tool_use), no dummy thinking block injected
+	parts := gjson.Get(outputStr, "request.contents.0.parts").Array()
+	if len(parts) != 1 {
+		t.Fatalf("Expected 1 part (tool only, no dummy injection), got %d", len(parts))
+	}
+
+	// Check function call conversion at parts[0]
+	funcCall := parts[0].Get("functionCall")
 	if !funcCall.Exists() {
-		t.Error("functionCall should exist")
+		t.Error("functionCall should exist at parts[0]")
 	}
 	if funcCall.Get("name").String() != "get_weather" {
 		t.Errorf("Expected function name 'get_weather', got '%s'", funcCall.Get("name").String())
@@ -203,6 +217,78 @@ func TestConvertClaudeRequestToAntigravity_ToolUse(t *testing.T) {
 	if funcCall.Get("id").String() != "call_123" {
 		t.Errorf("Expected function id 'call_123', got '%s'", funcCall.Get("id").String())
 	}
+	// Verify skip_thought_signature_validator is added (bypass for tools without valid thinking)
+	expectedSig := "skip_thought_signature_validator"
+	actualSig := parts[0].Get("thoughtSignature").String()
+	if actualSig != expectedSig {
+		t.Errorf("Expected thoughtSignature '%s', got '%s'", expectedSig, actualSig)
+	}
+}
+
+func TestConvertClaudeRequestToAntigravity_ToolUse_WithSignature(t *testing.T) {
+	validSignature := "abc123validSignature1234567890123456789012345678901234567890"
+	inputJSON := []byte(`{
+		"model": "claude-sonnet-4-5-thinking",
+		"messages": [
+			{
+				"role": "assistant",
+				"content": [
+					{"type": "thinking", "thinking": "Let me think...", "signature": "` + validSignature + `"},
+					{
+						"type": "tool_use",
+						"id": "call_123",
+						"name": "get_weather",
+						"input": "{\"location\": \"Paris\"}"
+					}
+				]
+			}
+		]
+	}`)
+
+	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5-thinking", inputJSON, false)
+	outputStr := string(output)
+
+	// Check function call has the signature from the preceding thinking block
+	part := gjson.Get(outputStr, "request.contents.0.parts.1")
+	if part.Get("functionCall.name").String() != "get_weather" {
+		t.Errorf("Expected functionCall, got %s", part.Raw)
+	}
+	if part.Get("thoughtSignature").String() != validSignature {
+		t.Errorf("Expected thoughtSignature '%s' on tool_use, got '%s'", validSignature, part.Get("thoughtSignature").String())
+	}
+}
+
+func TestConvertClaudeRequestToAntigravity_ReorderThinking(t *testing.T) {
+	// Case: text block followed by thinking block -> should be reordered to thinking first
+	validSignature := "abc123validSignature1234567890123456789012345678901234567890"
+	inputJSON := []byte(`{
+		"model": "claude-sonnet-4-5-thinking",
+		"messages": [
+			{
+				"role": "assistant",
+				"content": [
+					{"type": "text", "text": "Here is the plan."},
+					{"type": "thinking", "thinking": "Planning...", "signature": "` + validSignature + `"}
+				]
+			}
+		]
+	}`)
+
+	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5-thinking", inputJSON, false)
+	outputStr := string(output)
+
+	// Verify order: Thinking block MUST be first
+	parts := gjson.Get(outputStr, "request.contents.0.parts").Array()
+	if len(parts) != 2 {
+		t.Fatalf("Expected 2 parts, got %d", len(parts))
+	}
+
+	if !parts[0].Get("thought").Bool() {
+		t.Error("First part should be thinking block after reordering")
+	}
+	if parts[1].Get("text").String() != "Here is the plan." {
+		t.Error("Second part should be text block")
+	}
 }
 
 func TestConvertClaudeRequestToAntigravity_ToolResult(t *testing.T) {
@@ -402,8 +488,8 @@ func TestConvertClaudeRequestToAntigravity_TrailingSignedThinking_Kept(t *testin
 	}
 }
 
-func TestConvertClaudeRequestToAntigravity_MiddleUnsignedThinking_SentinelApplied(t *testing.T) {
-	// Middle message has unsigned thinking - should use sentinel (existing behavior)
+func TestConvertClaudeRequestToAntigravity_MiddleUnsignedThinking_Removed(t *testing.T) {
+	// Middle message has unsigned thinking - should be removed entirely
 	inputJSON := []byte(`{
 		"model": "claude-sonnet-4-5-thinking",
 		"messages": [
@@ -424,13 +510,18 @@ func TestConvertClaudeRequestToAntigravity_MiddleUnsignedThinking_SentinelApplie
 	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5-thinking", inputJSON, false)
 	outputStr := string(output)
 
-	// Middle unsigned thinking should have sentinel applied
-	thinkingPart := gjson.Get(outputStr, "request.contents.0.parts.0")
-	if !thinkingPart.Get("thought").Bool() {
-		t.Error("Middle thinking block should be preserved with sentinel")
+	// Unsigned thinking should be removed entirely
+	parts := gjson.Get(outputStr, "request.contents.0.parts").Array()
+	if len(parts) != 1 {
+		t.Fatalf("Expected 1 part (thinking removed), got %d", len(parts))
 	}
-	if thinkingPart.Get("thoughtSignature").String() != geminiCLIClaudeThoughtSignature {
-		t.Errorf("Middle unsigned thinking should use sentinel signature, got: %s", thinkingPart.Get("thoughtSignature").String())
+
+	// Only text part should remain
+	if parts[0].Get("thought").Bool() {
+		t.Error("Thinking block should be removed, not preserved")
+	}
+	if parts[0].Get("text").String() != "Answer" {
+		t.Errorf("Expected text 'Answer', got '%s'", parts[0].Get("text").String())
 	}
 }