diff --git a/internal/runtime/executor/antigravity_reasoning_replay.go b/internal/runtime/executor/antigravity_reasoning_replay.go
index fbe0fc28..7c8e93a0 100644
--- a/internal/runtime/executor/antigravity_reasoning_replay.go
+++ b/internal/runtime/executor/antigravity_reasoning_replay.go
@@ -1115,9 +1115,6 @@ func antigravityThoughtSignatureReplayPartPath(payload []byte, itemResult gjson.
 	if ci < 0 || ci >= len(contentArr) || !strings.EqualFold(strings.TrimSpace(contentArr[ci].Get("role").String()), "model") {
 		return "", false
 	}
-	if !antigravityReplayItemContextMatches(payload, itemResult, ci) {
-		return "", false
-	}
 	parts := contentArr[ci].Get("parts")
 	if !parts.IsArray() {
 		return "", false
@@ -1125,6 +1122,12 @@ func antigravityThoughtSignatureReplayPartPath(payload []byte, itemResult gjson.
 	partArr := parts.Array()
 	targetKind := strings.TrimSpace(itemResult.Get("targetKind").String())
 	targetHash := strings.TrimSpace(itemResult.Get("targetHash").String())
+	// A target hash pins the signature to a part whose own bytes are unchanged,
+	// which is all Gemini validates: the signature's own integrity, never its
+	// binding to the surrounding history. Drift elsewhere in the conversation
+	// therefore costs this signature nothing, so it is deliberately not gated on
+	// the context fingerprint. The fallback below has no such proof and stays
+	// gated.
 	if targetHash != "" {
 		if targetOccurrence := itemResult.Get("targetOccurrence"); targetOccurrence.Exists() {
 			wanted := int(targetOccurrence.Int())
@@ -1157,6 +1160,11 @@ func antigravityThoughtSignatureReplayPartPath(payload []byte, itemResult gjson.
 		return "", false
 	}
 
+	// No target hash: nothing proves which part this signature belongs to, so
+	// only a matching context fingerprint makes the positional guess safe.
+	if !antigravityReplayItemContextMatches(payload, itemResult, ci) {
+		return "", false
+	}
 	pi := int(itemResult.Get("partIndex").Int())
 	if pi >= 0 && pi < len(partArr) && partArr[pi].Type != gjson.Null {
 		if kind, _ := antigravityReplayPartFingerprint(partArr[pi]); kind != "" {
diff --git a/internal/runtime/executor/antigravity_reasoning_replay_test.go b/internal/runtime/executor/antigravity_reasoning_replay_test.go
index 1b05d8be..bfa508eb 100644
--- a/internal/runtime/executor/antigravity_reasoning_replay_test.go
+++ b/internal/runtime/executor/antigravity_reasoning_replay_test.go
@@ -1016,7 +1016,7 @@ func TestAntigravityReasoningReplayDoesNotCommitPartialResponse(t *testing.T) {
 	}
 }
 
-func TestPrepareAntigravityGeminiReasoningReplayRejectsFingerprintMismatch(t *testing.T) {
+func TestPrepareAntigravityGeminiReasoningReplayKeepsTextSignatureOnContextDrift(t *testing.T) {
 	internalcache.ClearAntigravityReasoningReplayCache()
 	t.Cleanup(internalcache.ClearAntigravityReasoningReplayCache)
 
@@ -1031,8 +1031,31 @@ func TestPrepareAntigravityGeminiReasoningReplayRejectsFingerprintMismatch(t *te
 	if errPrepare != nil {
 		t.Fatal(errPrepare)
 	}
+	// The signed part itself is byte-identical, so the signature still describes
+	// it exactly. Only the surrounding turns drifted, which Gemini does not bind
+	// signatures to, so dropping it here would only force needless re-reasoning.
+	if got := gjson.GetBytes(out, "request.contents.1.parts.0.thoughtSignature").String(); got != "fingerprinted-signature-123456" {
+		t.Fatalf("signature = %q, want the signature replayed even though the surrounding context drifted; body=%s", got, out)
+	}
+}
+
+func TestPrepareAntigravityGeminiReasoningReplayRejectsFingerprintMismatch(t *testing.T) {
+	internalcache.ClearAntigravityReasoningReplayCache()
+	t.Cleanup(internalcache.ClearAntigravityReasoningReplayCache)
+
+	kind, fingerprint := antigravityReplayPartFingerprint(gjson.Parse(`{"text":"original answer"}`))
+	item := buildAntigravityThoughtSignatureItem(1, 0, "fingerprinted-signature-123456", kind, fingerprint)
+	internalcache.CacheAntigravityReasoningReplayItems("gemini-3.6-flash-high", "session:edited", [][]byte{item})
+
+	// The client rewrote the signed part, so the cached signature describes text
+	// that is no longer in the request and must not be attached to the new text.
+	payload := []byte(`{"sessionId":"edited","request":{"contents":[{"role":"user","parts":[{"text":"turn"}]},{"role":"model","parts":[{"text":"edited answer"}]},{"role":"user","parts":[{"text":"next"}]}]}}`)
+	out, _, errPrepare := prepareAntigravityGeminiReasoningReplayPayload(context.Background(), "gemini-3.6-flash-high", cliproxyexecutor.Request{}, cliproxyexecutor.Options{}, payload)
+	if errPrepare != nil {
+		t.Fatal(errPrepare)
+	}
 	if got := gjson.GetBytes(out, "request.contents.1.parts.0.thoughtSignature").String(); got != "" {
-		t.Fatalf("mismatched rebuilt context received stale signature %q; body=%s", got, out)
+		t.Fatalf("edited part received stale signature %q; body=%s", got, out)
 	}
 }