From 41ae2c81e7543405de48cba40f1c095a83f16715 Mon Sep 17 00:00:00 2001
From: sususu98 <suchangshan@foxmail.com>
Date: Mon, 13 Apr 2026 17:38:43 +0800
Subject: [PATCH] fix(antigravity): discard thinking blocks with
 non-Claude-format signatures

Proxy-generated thinking blocks may carry hex hashes or other non-Claude
signatures (e.g. "d5cb9cd0823142109f451861") from Gemini responses. These
are now discarded alongside empty-signature blocks during the strip phase,
before validation runs. Valid Claude signatures always start with 'E' or 'R'
(after stripping any cache prefix).
---
 .../claude/signature_validation.go            | 26 ++++++++++++++++---
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/internal/translator/antigravity/claude/signature_validation.go b/internal/translator/antigravity/claude/signature_validation.go
index f4fef08c6..63203abdc 100644
--- a/internal/translator/antigravity/claude/signature_validation.go
+++ b/internal/translator/antigravity/claude/signature_validation.go
@@ -73,9 +73,10 @@ type claudeSignatureTree struct {
 	HasField7           bool
 }
 
-// StripEmptySignatureThinkingBlocks removes thinking blocks with empty signatures
-// from messages[].content[]. These come from proxy-generated responses (Antigravity/Gemini)
-// where no real Claude signature exists.
+// StripInvalidSignatureThinkingBlocks removes thinking blocks whose signatures
+// are empty or not valid Claude format (must start with 'E' or 'R' after
+// stripping any cache prefix). These come from proxy-generated responses
+// (Antigravity/Gemini) where no real Claude signature exists.
 func StripEmptySignatureThinkingBlocks(payload []byte) []byte {
 	messages := gjson.GetBytes(payload, "messages")
 	if !messages.IsArray() {
@@ -90,7 +91,7 @@ func StripEmptySignatureThinkingBlocks(payload []byte) []byte {
 		var kept []string
 		stripped := false
 		for _, part := range content.Array() {
-			if part.Get("type").String() == "thinking" && strings.TrimSpace(part.Get("signature").String()) == "" {
+			if part.Get("type").String() == "thinking" && !hasValidClaudeSignature(part.Get("signature").String()) {
 				stripped = true
 				continue
 			}
@@ -111,6 +112,23 @@ func StripEmptySignatureThinkingBlocks(payload []byte) []byte {
 	return payload
 }
 
+// hasValidClaudeSignature returns true if sig looks like a real Claude thinking
+// signature: non-empty and starts with 'E' or 'R' (after stripping optional
+// cache prefix like "modelGroup#").
+func hasValidClaudeSignature(sig string) bool {
+	sig = strings.TrimSpace(sig)
+	if sig == "" {
+		return false
+	}
+	if idx := strings.IndexByte(sig, '#'); idx >= 0 {
+		sig = strings.TrimSpace(sig[idx+1:])
+	}
+	if sig == "" {
+		return false
+	}
+	return sig[0] == 'E' || sig[0] == 'R'
+}
+
 func ValidateClaudeBypassSignatures(inputRawJSON []byte) error {
 	messages := gjson.GetBytes(inputRawJSON, "messages")
 	if !messages.IsArray() {