Render agent message sends as chat bubbles

Co-authored-by: Rizz <302abe414ca6e3134763d2539bfcf145aea2a63fe5f8455204ed602fd40cf381@buzz.block.builderlab.xyz>

Signed-off-by: Rizz <302abe414ca6e3134763d2539bfcf145aea2a63fe5f8455204ed602fd40cf381@buzz.block.builderlab.xyz>
(cherry picked from commit 62b9603bac)
Signed-off-by: ss-dev-00 <a02c4e0850e5e612b4ddf95dbe2f5c56467cf27c6552203bc833ff438fb31971@buzz.block.builderlab.xyz>

desktop/src/features/agents/ui/AgentSessionToolItem/ToolItem.tsx

@@ -59,9 +59,10 @@ export function ToolItem({
     [],
   );
 
-  // On a work block's rail a posted message is a step the agent took, so it
-  // takes the same muted, expandable row as every other step. Everywhere else
-  // it keeps the bubble: see `useIsInsideWorkBlockRail`.
+  // Message presentations keep their readable bubble whenever they are standalone.
+  // The conversation grouping keeps message sends standalone rather than placing
+  // them on a work block rail; this guard preserves the muted row if another
+  // transcript composition explicitly embeds one in a rail.
   if (compactSummary.presentation === "message" && !insideWorkBlockRail) {
     return (
       <div

desktop/src/features/agents/ui/agentSessionWorkBlockGrouping.test.mjs

@@ -210,6 +210,34 @@ test("the plan stays a sibling and splits the work around it", () => {
   assert.deepEqual(blockItemIds(grouped[2]), ["tool:2"]);
 });
 
+test("message sends stay outside the work block as chat bubbles", () => {
+  const send = tool("tool:send", {
+    args: { content: "Posted an update" },
+    buzzToolName: "send_message",
+    descriptor: {
+      renderClass: "message",
+      label: "Sent message",
+      preview: "Posted an update",
+      tone: "neutral",
+      source: "buzz",
+    },
+    renderClass: "message",
+    toolName: "send_message",
+  });
+  const grouped = groupConversationWorkBlocks(
+    itemSegments(tool("tool:1"), send, tool("tool:2")),
+  );
+
+  assert.deepEqual(kinds(grouped), ["work-block", "item", "work-block"]);
+  assert.deepEqual(blockItemIds(grouped[0]), ["tool:1"]);
+  assert.equal(
+    grouped[1].item.id,
+    "tool:send",
+    "the existing message presenter can render the send as a readable bubble",
+  );
+  assert.deepEqual(blockItemIds(grouped[2]), ["tool:2"]);
+});
+
 test("permission gates and errors stay loud, in position", () => {
   for (const renderClass of ["permission", "error", "status"]) {
     const grouped = groupConversationWorkBlocks(

desktop/src/features/agents/ui/agentSessionWorkBlockGrouping.ts

@@ -2,6 +2,7 @@ import type {
   TranscriptTurnSegment,
   TranscriptDisplayBlock,
 } from "./agentSessionTranscriptGrouping";
+import { buildCompactToolSummary } from "./agentSessionToolSummary";
 import type { TranscriptItem } from "./agentSessionTypes";
 
 /** Reasoning. */
@@ -63,12 +64,14 @@ export type TranscriptConversationSegment =
  * Which items are *work* — the material the block absorbs.
  *
  *  - **thoughts** — reasoning is a step on the rail, not a sibling disclosure.
- *  - **tool steps**, including failed ones. A failure belongs to the work it
- *    happened in; the folded line reports it (`N steps · 1 failed`) so it is
- *    never hidden behind a neutral count.
+ *  - **tool steps**, including failed ones, except message sends. A failure
+ *    belongs to the work it happened in; the folded line reports it
+ *    (`N steps · 1 failed`) so it is never hidden behind a neutral count.
+ *    Message sends stay outside as chat bubbles: they are communication the
+ *    reader should be able to read and open, not generic work telemetry.
  *  - **interim agent notes** — an assistant message that is not the turn's
- *    answer. A relay post the agent makes mid-turn is a tool step and lands
- *    here for the same reason: it reads as progress, not as the reply.
+ *    answer. Unlike a message-send tool, a note is narration within the turn,
+ *    so it stays on the rail as progress.
  *
  * Everything else stays outside and keeps its own row. Plans stay a sibling
  * (Buzz's checklist is a first-class surface, not a step), and lifecycle rows —
@@ -84,7 +87,10 @@ function isWorkItem(
   item: TranscriptItem,
   finalAnswerId: string | null,
 ): item is WorkBlockItem {
-  if (item.type === "thought" || item.type === "tool") return true;
+  if (item.type === "thought") return true;
+  if (item.type === "tool") {
+    return buildCompactToolSummary(item).presentation !== "message";
+  }
   return (
     item.type === "message" &&
     item.role === "assistant" &&