refactor: stop rewriting tool descriptions; keep only system sentence rewrite

backend/internal/service/gateway_sanitize_test.go

@@ -13,8 +13,9 @@ func TestSanitizeOpenCodeText_RewritesCanonicalSentence(t *testing.T) {
 	require.Equal(t, strings.TrimSpace(claudeCodeSystemPrompt), got)
 }
 
-func TestSanitizeToolText_RewritesOpenCodeKeywords(t *testing.T) {
+func TestSanitizeToolDescription_DoesNotRewriteKeywords(t *testing.T) {
 	in := "OpenCode and opencode are mentioned."
-	got := sanitizeToolText(in)
-	require.Equal(t, "Claude Code and Claude are mentioned.", got)
+	got := sanitizeToolDescription(in)
+	// We no longer rewrite tool descriptions; only redact obvious path leaks.
+	require.Equal(t, in, got)
 }

backend/internal/service/gateway_service.go

@@ -715,26 +715,15 @@ func sanitizeSystemText(text string) string {
 	return text
 }
 
-// sanitizeToolText is intentionally more aggressive than sanitizeSystemText because
-// tool descriptions are not user chat content, and some upstreams may flag "opencode"
-// strings as non-Claude-Code fingerprints.
-func sanitizeToolText(text string) string {
-	if text == "" {
-		return text
-	}
-	text = sanitizeSystemText(text)
-	text = strings.ReplaceAll(text, "OpenCode", "Claude Code")
-	text = opencodeTextRe.ReplaceAllString(text, "Claude")
-	return text
-}
-
 func sanitizeToolDescription(description string) string {
 	if description == "" {
 		return description
 	}
 	description = toolDescAbsPathRe.ReplaceAllString(description, "[path]")
 	description = toolDescWinPathRe.ReplaceAllString(description, "[path]")
-	return sanitizeToolText(description)
+	// Intentionally do NOT rewrite tool descriptions (OpenCode/Claude strings).
+	// Tool names/skill names may rely on exact wording, and rewriting can be misleading.
+	return description
 }
 
 func normalizeToolInputSchema(inputSchema any, cache map[string]string) {