fix(chat): an edit after a broken edit call no longer fails, found with Opus 5.5

- Claude Opus 5.5 sent an edit with invalid JSON, then the same edit
  again. The first call's streamed preview was never undone: its input
  has no operations, and the undo sat behind that check. The second edit
  then started from the preview, failed on a duplicate id, and the model
  had to try a third time. The undo now runs first, and an edit that
  starts in the same render uses the undone diagram.
- The SDK passes an invalid tool call's error as a string, which was
  wrapped as a provider error. streamErrorText keeps it as the text the
  model reads.
- Bedrock's "on-demand throughput isn't supported" gets the model id hint.
- The thinking header uses the page language ("Thought for 1 second" in
  English), from the dictionary entries that were already there.

lib/llm-errors.ts

@@ -49,6 +49,8 @@ const SPECIFIC_TEXTS: Array<[RegExp, LLMErrorCode]> = [
     ],
     // Bedrock, when the output limit cut the tool call's JSON short
     [/toolUse\.input is invalid/i, "output_truncated"],
+    // Bedrock, for a model id without the inference profile prefix
+    [/on-demand throughput isn.t supported/i, "model_not_found"],
     [
         /insufficient[_ ]quota|insufficient balance|exceeded your current quota|credit balance is too low|余额不足/i,
         "insufficient_quota",
@@ -105,6 +107,17 @@ function problemDetail(body: string): string | undefined {
     }
 }
 
+/**
+ * The error text for the chat stream: what went wrong with the provider as
+ * JSON for the hint, or the text the model must read to fix a tool call.
+ */
+export function streamErrorText(error: unknown): string {
+    // The SDK passes an invalid tool call's error as a plain string
+    if (typeof error === "string") return error
+    if (isToolCallError(error)) return (error as Error).message
+    return JSON.stringify(classifyLLMError(error))
+}
+
 /**
  * Model and tool errors the SDK sends back to the model as the tool result,
  * so it can fix its call. Their text has to stay as it is.