diff --git a/desktop/src/features/agents/ui/AgentSessionTranscriptList.tsx b/desktop/src/features/agents/ui/AgentSessionTranscriptList.tsx
index 08bc730a3..019b4d7d9 100644
--- a/desktop/src/features/agents/ui/AgentSessionTranscriptList.tsx
+++ b/desktop/src/features/agents/ui/AgentSessionTranscriptList.tsx
@@ -26,6 +26,9 @@ import { buildTranscriptPresentation } from "./agentSessionTranscriptPresentatio
 import { formatTranscriptTime } from "./agentSessionUtils";
 import { Tooltip, TooltipContent, TooltipTrigger } from "@/shared/ui/tooltip";
 
+/** Dev-only: surface the observer wire label that produced each transcript row. */
+const SHOW_TRANSCRIPT_ACP_SOURCE = import.meta.env.DEV;
+
 export function AgentSessionTranscriptList({
   agentName,
   compact = false,
@@ -87,6 +90,9 @@ export function AgentSessionTranscriptList({
             )}
             key={item.id}
           >
+            {SHOW_TRANSCRIPT_ACP_SOURCE && item.acpSource ? (
+              <TranscriptAcpSourceBadge source={item.acpSource} />
+            ) : null}
             <TranscriptItemView
               agentName={agentName}
               compact={compact}
@@ -101,6 +107,18 @@ export function AgentSessionTranscriptList({
   );
 }
 
+function TranscriptAcpSourceBadge({ source }: { source: string }) {
+  return (
+    <span
+      className="mb-1 inline-flex max-w-full rounded border border-amber-500/25 bg-amber-500/10 px-1.5 py-0.5 font-mono text-[10px] leading-none text-amber-800 dark:text-amber-200"
+      data-testid="transcript-acp-source"
+      title={`ACP wire source: ${source}`}
+    >
+      {source}
+    </span>
+  );
+}
+
 function TranscriptNowSummary({
   agentName,
   compact,
diff --git a/desktop/src/features/agents/ui/agentSessionTranscript.test.mjs b/desktop/src/features/agents/ui/agentSessionTranscript.test.mjs
new file mode 100644
index 000000000..dda17b174
--- /dev/null
+++ b/desktop/src/features/agents/ui/agentSessionTranscript.test.mjs
@@ -0,0 +1,60 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { buildTranscript } from "./agentSessionTranscript.ts";
+
+test("buildTranscript tags assistant chunks with agent_message_chunk", () => {
+  const items = buildTranscript([
+    {
+      seq: 1,
+      timestamp: "2026-06-14T20:47:14.000Z",
+      kind: "acp_read",
+      agentIndex: 0,
+      channelId: "channel-1",
+      sessionId: "sess-1",
+      turnId: "turn-1",
+      payload: {
+        method: "session/update",
+        params: {
+          update: {
+            sessionUpdate: "agent_message_chunk",
+            messageId: "msg-1",
+            content: [{ type: "text", text: "Marge is summoned." }],
+          },
+        },
+      },
+    },
+  ]);
+
+  assert.equal(items.length, 1);
+  assert.equal(items[0]?.type, "message");
+  assert.equal(items[0]?.acpSource, "agent_message_chunk");
+});
+
+test("buildTranscript tags thought chunks with agent_thought_chunk", () => {
+  const items = buildTranscript([
+    {
+      seq: 2,
+      timestamp: "2026-06-14T20:47:15.000Z",
+      kind: "acp_read",
+      agentIndex: 0,
+      channelId: "channel-1",
+      sessionId: "sess-1",
+      turnId: "turn-1",
+      payload: {
+        method: "session/update",
+        params: {
+          update: {
+            sessionUpdate: "agent_thought_chunk",
+            messageId: "thought-1",
+            content: [{ type: "text", text: "Considering next step." }],
+          },
+        },
+      },
+    },
+  ]);
+
+  assert.equal(items.length, 1);
+  assert.equal(items[0]?.type, "thought");
+  assert.equal(items[0]?.acpSource, "agent_thought_chunk");
+});
diff --git a/desktop/src/features/agents/ui/agentSessionTranscript.ts b/desktop/src/features/agents/ui/agentSessionTranscript.ts
index 60cf7f62b..62d642f59 100644
--- a/desktop/src/features/agents/ui/agentSessionTranscript.ts
+++ b/desktop/src/features/agents/ui/agentSessionTranscript.ts
@@ -117,6 +117,7 @@ function upsertMessage(
   timestamp: string,
   channelId: string | null,
   authorPubkey: string | null = null,
+  acpSource?: string,
 ) {
   const currentKey = d.activeMessageKey.get(id);
 
@@ -128,6 +129,7 @@ function upsertMessage(
         text: existing.text + text,
         channelId,
         authorPubkey: authorPubkey ?? existing.authorPubkey,
+        acpSource: acpSource ?? existing.acpSource,
       });
       return;
     }
@@ -144,6 +146,7 @@ function upsertMessage(
     timestamp,
     channelId,
     authorPubkey,
+    acpSource,
   });
   d.activeMessageKey = new Map(d.activeMessageKey);
   d.activeMessageKey.set(id, newKey);
@@ -157,14 +160,20 @@ function upsertTextItem(
   text: string,
   timestamp: string,
   channelId: string | null,
+  acpSource?: string,
 ) {
   const existing = d.itemsById.get(id);
   if (existing && existing.type === type) {
-    replaceItem(d, id, { ...existing, text: existing.text + text, channelId });
+    replaceItem(d, id, {
+      ...existing,
+      text: existing.text + text,
+      channelId,
+      acpSource: acpSource ?? existing.acpSource,
+    });
     return;
   }
   sealOpenMessages(d);
-  pushItem(d, { id, type, title, text, timestamp, channelId });
+  pushItem(d, { id, type, title, text, timestamp, channelId, acpSource });
 }
 
 function upsertMetadata(
@@ -174,14 +183,28 @@ function upsertMetadata(
   sections: PromptSection[],
   timestamp: string,
   channelId: string | null,
+  acpSource?: string,
 ) {
   const existing = d.itemsById.get(id);
   if (existing?.type === "metadata") {
-    replaceItem(d, id, { ...existing, sections, channelId });
+    replaceItem(d, id, {
+      ...existing,
+      sections,
+      channelId,
+      acpSource: acpSource ?? existing.acpSource,
+    });
     return;
   }
   sealOpenMessages(d);
-  pushItem(d, { id, type: "metadata", title, sections, timestamp, channelId });
+  pushItem(d, {
+    id,
+    type: "metadata",
+    title,
+    sections,
+    timestamp,
+    channelId,
+    acpSource,
+  });
 }
 
 function upsertTool(
@@ -196,6 +219,7 @@ function upsertTool(
   isError: boolean,
   timestamp: string,
   channelId: string | null,
+  acpSource?: string,
 ) {
   const existing = d.itemsById.get(id);
   const canonicalBuzzToolName =
@@ -225,6 +249,7 @@ function upsertTool(
           ? timestamp
           : existing.completedAt,
       channelId,
+      acpSource: acpSource ?? existing.acpSource,
     });
     return;
   }
@@ -243,6 +268,7 @@ function upsertTool(
     startedAt: timestamp,
     completedAt: null,
     channelId,
+    acpSource,
   });
 }
 
@@ -268,6 +294,7 @@ export function processTranscriptEvent(
       describeTurnStarted(event.payload),
       event.timestamp,
       channelId,
+      event.kind,
     );
   } else if (event.kind === "session_resolved") {
     upsertTextItem(
@@ -278,6 +305,7 @@ export function processTranscriptEvent(
       describeSessionResolved(event.payload),
       event.timestamp,
       channelId,
+      event.kind,
     );
   } else if (event.kind === "acp_parse_error") {
     upsertTextItem(
@@ -288,6 +316,7 @@ export function processTranscriptEvent(
       extractBlockText(event.payload),
       event.timestamp,
       channelId,
+      event.kind,
     );
   } else if (event.kind === "turn_error" || event.kind === "agent_panic") {
     const payload = asRecord(event.payload);
@@ -303,6 +332,7 @@ export function processTranscriptEvent(
       `${outcome}: ${error}`,
       event.timestamp,
       channelId,
+      event.kind,
     );
   } else if (event.kind === "acp_read" || event.kind === "acp_write") {
     const payload = asRecord(event.payload);
@@ -322,6 +352,7 @@ export function processTranscriptEvent(
             event.timestamp,
             channelId,
             parsedPrompt.userPubkey,
+            "session/prompt:user",
           );
         }
         if (parsedPrompt.sections.length > 0) {
@@ -332,6 +363,7 @@ export function processTranscriptEvent(
             parsedPrompt.sections,
             event.timestamp,
             channelId,
+            "session/prompt:context",
           );
         }
       }
@@ -351,6 +383,8 @@ export function processTranscriptEvent(
           extractContentText(update.content),
           event.timestamp,
           channelId,
+          null,
+          updateType,
         );
       } else if (updateType === "user_message_chunk") {
         upsertMessage(
@@ -361,6 +395,8 @@ export function processTranscriptEvent(
           extractContentText(update.content),
           event.timestamp,
           channelId,
+          null,
+          updateType,
         );
       } else if (updateType === "agent_thought_chunk") {
         upsertTextItem(
@@ -371,6 +407,7 @@ export function processTranscriptEvent(
           extractContentText(update.content),
           event.timestamp,
           channelId,
+          updateType,
         );
       } else if (updateType === "tool_call") {
         const toolId = asString(update.toolCallId) ?? `tool:${event.seq}`;
@@ -387,6 +424,7 @@ export function processTranscriptEvent(
           false,
           event.timestamp,
           channelId,
+          updateType,
         );
       } else if (updateType === "tool_call_update") {
         const toolId = asString(update.toolCallId) ?? `tool:${event.seq}`;
@@ -406,6 +444,7 @@ export function processTranscriptEvent(
           status === "failed",
           event.timestamp,
           channelId,
+          updateType,
         );
       } else if (updateType === "plan") {
         upsertTextItem(
@@ -416,6 +455,7 @@ export function processTranscriptEvent(
           extractContentText(update.content) || JSON.stringify(update, null, 2),
           event.timestamp,
           channelId,
+          updateType,
         );
       }
     }
diff --git a/desktop/src/features/agents/ui/agentSessionTypes.ts b/desktop/src/features/agents/ui/agentSessionTypes.ts
index 2ff4ea305..90fb2500e 100644
--- a/desktop/src/features/agents/ui/agentSessionTypes.ts
+++ b/desktop/src/features/agents/ui/agentSessionTypes.ts
@@ -20,6 +20,9 @@ export type ConnectionState =
 
 export type ToolStatus = "executing" | "completed" | "failed" | "pending";
 
+/** Observer/ACP wire label for dev-only transcript debugging. */
+export type TranscriptAcpSource = string;
+
 export type TranscriptItem =
   | {
       id: string;
@@ -28,6 +31,7 @@ export type TranscriptItem =
       title: string;
       text: string;
       timestamp: string;
+      acpSource?: TranscriptAcpSource;
       authorPubkey?: string | null;
       channelId?: string | null;
     }
@@ -37,6 +41,7 @@ export type TranscriptItem =
       title: string;
       text: string;
       timestamp: string;
+      acpSource?: TranscriptAcpSource;
       channelId?: string | null;
     }
   | {
@@ -45,6 +50,7 @@ export type TranscriptItem =
       title: string;
       text: string;
       timestamp: string;
+      acpSource?: TranscriptAcpSource;
       channelId?: string | null;
     }
   | {
@@ -53,6 +59,7 @@ export type TranscriptItem =
       title: string;
       sections: PromptSection[];
       timestamp: string;
+      acpSource?: TranscriptAcpSource;
       channelId?: string | null;
     }
   | {
@@ -68,6 +75,7 @@ export type TranscriptItem =
       timestamp: string;
       startedAt: string;
       completedAt: string | null;
+      acpSource?: TranscriptAcpSource;
       channelId?: string | null;
     };