diff --git a/open-sse/translator/helpers/claudeHelper.ts b/open-sse/translator/helpers/claudeHelper.ts
index 2936b60240..bf4e589d0f 100644
--- a/open-sse/translator/helpers/claudeHelper.ts
+++ b/open-sse/translator/helpers/claudeHelper.ts
@@ -247,10 +247,16 @@ export function prepareClaudeRequest(
           let hasToolUse = false;
           let hasThinking = false;
 
-          // Always replace signature for all thinking blocks
+          // Convert thinking blocks to redacted_thinking and replace signature.
+          // When requests cross provider boundaries (e.g., combo fallback), the
+          // original thinking signature is invalid for the new provider, causing
+          // "Invalid signature in thinking block" 400 errors. redacted_thinking
+          // blocks are accepted without signature validation.
           for (const block of content) {
             if (block.type === "thinking" || block.type === "redacted_thinking") {
+              block.type = "redacted_thinking";
               block.signature = DEFAULT_THINKING_CLAUDE_SIGNATURE;
+              delete block.thinking;
               hasThinking = true;
             }
             if (block.type === "tool_use") hasToolUse = true;
diff --git a/src/shared/utils/clipboard.ts b/src/shared/utils/clipboard.ts
index ee6d014dfb..50f6671dc9 100644
--- a/src/shared/utils/clipboard.ts
+++ b/src/shared/utils/clipboard.ts
@@ -11,13 +11,10 @@
  * @returns true if copy succeeded, false otherwise
  */
 export async function copyToClipboard(text: string): Promise<boolean> {
-  // Method 1: Clipboard API (requires HTTPS / secure context)
-  if (
-    typeof navigator !== "undefined" &&
-    navigator.clipboard &&
-    typeof window !== "undefined" &&
-    window.isSecureContext
-  ) {
+  // Method 1: Clipboard API
+  // Works on HTTPS, localhost (treated as secure context), and some browsers
+  // even on HTTP. Try unconditionally — the catch handles failures.
+  if (typeof navigator !== "undefined" && navigator.clipboard) {
     try {
       await navigator.clipboard.writeText(text);
       return true;
diff --git a/tests/unit/translator-helper-branches.test.ts b/tests/unit/translator-helper-branches.test.ts
index e31c393352..33a59a0302 100644
--- a/tests/unit/translator-helper-branches.test.ts
+++ b/tests/unit/translator-helper-branches.test.ts
@@ -306,9 +306,10 @@ test("claudeHelper validates content, ordering and request preparation branches"
   assert.equal(prepared.messages[4].content[0].type, "tool_result");
   assert.deepEqual(
     prepared.messages[5].content.map((block) => block.type),
-    ["thinking", "text"]
+    ["redacted_thinking", "text"]
   );
   assert.ok(prepared.messages[5].content[0].signature);
+  assert.equal(prepared.messages[5].content[0].thinking, undefined);
   assert.equal(prepared.tools.length, 2);
   assert.equal(prepared.tools[0].cache_control, undefined);
   assert.deepEqual(prepared.tools[1].cache_control, { type: "ephemeral", ttl: "1h" });