refactor(translator): remove session ID logic from signature caching and associated tests

internal/translator/antigravity/claude/antigravity_claude_request.go

@@ -7,8 +7,6 @@ package claude
 
 import (
 	"bytes"
-	"crypto/sha256"
-	"encoding/hex"
 	"strings"
 
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/cache"
@@ -19,33 +17,6 @@ import (
 	"github.com/tidwall/sjson"
 )
 
-// deriveSessionID generates a stable session ID from the request.
-// Uses the hash of the first user message to identify the conversation.
-func deriveSessionID(rawJSON []byte) string {
-	userIDResult := gjson.GetBytes(rawJSON, "metadata.user_id")
-	if userIDResult.Exists() {
-		userID := userIDResult.String()
-		idx := strings.Index(userID, "session_")
-		if idx != -1 {
-			return userID[idx+8:]
-		}
-	}
-	messages := gjson.GetBytes(rawJSON, "messages")
-	if !messages.IsArray() {
-		return ""
-	}
-	for _, msg := range messages.Array() {
-		if msg.Get("role").String() == "user" {
-			content := msg.Get("content").Raw
-			if content != "" {
-				h := sha256.Sum256([]byte(content))
-				return hex.EncodeToString(h[:16])
-			}
-		}
-	}
-	return ""
-}
-
 // ConvertClaudeRequestToAntigravity parses and transforms a Claude Code API request into Gemini CLI API format.
 // It extracts the model name, system instruction, message contents, and tool declarations
 // from the raw JSON request and returns them in the format expected by the Gemini CLI API.
@@ -68,9 +39,6 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 	enableThoughtTranslate := true
 	rawJSON := bytes.Clone(inputRawJSON)
 
-	// Derive session ID for signature caching
-	sessionID := deriveSessionID(rawJSON)
-
 	// system instruction
 	systemInstructionJSON := ""
 	hasSystemInstruction := false
@@ -133,7 +101,7 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 						// Always try cached signature first (more reliable than client-provided)
 						// Client may send stale or invalid signatures from different sessions
 						signature := ""
-						if sessionID != "" && thinkingText != "" {
+						if thinkingText != "" {
 							if cachedSig := cache.GetCachedSignature(modelName, thinkingText); cachedSig != "" {
 								signature = cachedSig
 								// log.Debugf("Using cached signature for thinking block")