fix: print the running tool once, not twice (#17)

src/lib/markdown.ts

@@ -1,5 +1,6 @@
 import { imageSource } from "./attachments";
 import { repairCodeBlocks } from "./code";
+import { describeActivity } from "./thread";
 import type { Attachment, ChatTurn, ThreadMessage } from "./types";
 
 /**
@@ -82,17 +83,37 @@ function renderMessage(message: ThreadMessage, options: TranscriptOptions): stri
   }
 
   // While a tool is running there is no answer text yet, so the activity line
-  // stands in and the user can see what Lam is actually doing.
-  const placeholder = message.status ? `_${message.status}…_` : "_Thinking…_";
-  const body = message.text.trim()
+  // stands in and the user can see what Lam is actually doing. It is shown
+  // whether or not tokens have arrived, because a tool that starts after the
+  // answer has begun would otherwise be invisible for the rest of the turn.
+  const activityLine =
+    message.isStreaming && message.activity ? `_${describeActivity(message.activity)}…_` : undefined;
+
+  /** The answer, or whatever stands in for it while there is none. */
+  const answered = message.text.trim();
+  const body = answered
     ? // Fences without a language render as a plain dark panel, and a lone
       // inline command renders as a chip with no Copy button at all. Both are
       // repaired before the markdown reaches the renderer.
-      repairCodeBlocks(message.text.trim())
-    : message.isStreaming
-      ? placeholder
-      : "_No response._";
-  const sections = [message.isStreaming ? `${body} ${STREAMING_CURSOR}` : body];
+      repairCodeBlocks(answered)
+    : !message.isStreaming
+      ? "_No response._"
+      : activityLine
+        ? // The activity line above is already saying what is being waited on, so
+          // printing the placeholder as well put the same sentence on screen
+          // twice: once as a note above the transcript and once as the stand-in.
+          undefined
+        : message.status
+          ? `_${message.status}…_`
+          : "_Thinking…_";
+
+  // The cursor trails whichever of the two is written last, so it always sits at
+  // the end of the text arriving rather than on a line of its own.
+  const written = [activityLine, body].filter((line): line is string => Boolean(line));
+  const last = written.length - 1;
+  const sections = written.map((line, index) =>
+    message.isStreaming && index === last ? `${line} ${STREAMING_CURSOR}` : line,
+  );
 
   // The one thing allowed to break the plain-text rule, because it means
   // something went wrong and should not be skimmed past.