diff --git a/src/cli/run/event-handlers.ts b/src/cli/run/event-handlers.ts
index 885cd4c5..1ee2f358 100644
--- a/src/cli/run/event-handlers.ts
+++ b/src/cli/run/event-handlers.ts
@@ -187,6 +187,7 @@ function handleToolPart(
   const status = part.state?.status
 
   if (status === "running") {
+    if (state.currentTool !== null) return
     state.currentTool = toolName
     const header = formatToolHeader(toolName, part.state?.input ?? {})
     const suffix = header.description ? ` ${pc.dim(header.description)}` : ""
@@ -195,6 +196,7 @@ function handleToolPart(
   }
 
   if (status === "completed" || status === "error") {
+    if (state.currentTool === null) return
     const output = part.state?.output || ""
     if (output.trim()) {
       process.stdout.write(pc.dim(`  ${displayChars.treeEnd} output  \n`))
@@ -216,7 +218,7 @@ export function handleMessageUpdated(ctx: RunContext, payload: EventPayload, sta
 
   state.currentMessageRole = props?.info?.role ?? null
 
-  const messageID = props?.info?.id
+  const messageID = props?.info?.id ?? null
   const role = props?.info?.role
   if (messageID && role) {
     state.messageRoleById[messageID] = role
@@ -224,15 +226,19 @@ export function handleMessageUpdated(ctx: RunContext, payload: EventPayload, sta
 
   if (props?.info?.role !== "assistant") return
 
-  state.hasReceivedMeaningfulWork = true
-  state.messageCount++
-  state.lastPartText = ""
-  state.lastReasoningText = ""
-  state.hasPrintedThinkingLine = false
-  state.lastThinkingSummary = ""
-  state.textAtLineStart = true
-  state.thinkingAtLineStart = false
-  closeThinkBlockIfNeeded(state)
+  const isNewMessage = !messageID || messageID !== state.currentMessageId
+  if (isNewMessage) {
+    state.currentMessageId = messageID
+    state.hasReceivedMeaningfulWork = true
+    state.messageCount++
+    state.lastPartText = ""
+    state.lastReasoningText = ""
+    state.hasPrintedThinkingLine = false
+    state.lastThinkingSummary = ""
+    state.textAtLineStart = true
+    state.thinkingAtLineStart = false
+    closeThinkBlockIfNeeded(state)
+  }
 
   const agent = props?.info?.agent ?? null
   const model = props?.info?.modelID ?? null
@@ -253,6 +259,8 @@ export function handleToolExecute(ctx: RunContext, payload: EventPayload, state:
 
   closeThinkBlockIfNeeded(state)
 
+  if (state.currentTool !== null) return
+
   const toolName = props?.name || "unknown"
   state.currentTool = toolName
   const header = formatToolHeader(toolName, props?.input ?? {})
@@ -270,6 +278,8 @@ export function handleToolResult(ctx: RunContext, payload: EventPayload, state:
 
   closeThinkBlockIfNeeded(state)
 
+  if (state.currentTool === null) return
+
   const output = props?.output || ""
   if (output.trim()) {
     process.stdout.write(pc.dim(`  ${displayChars.treeEnd} output  \n`))
diff --git a/src/cli/run/event-state.ts b/src/cli/run/event-state.ts
index db485707..9caac122 100644
--- a/src/cli/run/event-state.ts
+++ b/src/cli/run/event-state.ts
@@ -37,6 +37,8 @@ export interface EventState {
   textAtLineStart: boolean
   /** Whether reasoning stream is currently at line start (for padding) */
   thinkingAtLineStart: boolean
+  /** Current assistant message ID — prevents counter resets on repeated message.updated for same message */
+  currentMessageId: string | null
 }
 
 export function createEventState(): EventState {
@@ -63,5 +65,6 @@ export function createEventState(): EventState {
     lastThinkingSummary: "",
     textAtLineStart: true,
     thinkingAtLineStart: false,
+    currentMessageId: null,
   }
 }
diff --git a/src/cli/run/message-part-delta.test.ts b/src/cli/run/message-part-delta.test.ts
index 379572c0..c5bba429 100644
--- a/src/cli/run/message-part-delta.test.ts
+++ b/src/cli/run/message-part-delta.test.ts
@@ -462,4 +462,187 @@ describe("message.part.delta handling", () => {
     expect(rendered).toContain("END-OF-TOOL-OUTPUT-MARKER")
     stdoutSpy.mockRestore()
   })
+
+  it("renders tool header only once when message.part.updated fires multiple times for same running tool", async () => {
+    //#given
+    const ctx = createMockContext("ses_main")
+    const state = createEventState()
+    const stdoutSpy = spyOn(process.stdout, "write").mockImplementation(() => true)
+    const events: EventPayload[] = [
+      {
+        type: "message.part.updated",
+        properties: {
+          part: {
+            id: "tool-1",
+            sessionID: "ses_main",
+            type: "tool",
+            tool: "bash",
+            state: { status: "running", input: { command: "bun test" } },
+          },
+        },
+      },
+      {
+        type: "message.part.updated",
+        properties: {
+          part: {
+            id: "tool-1",
+            sessionID: "ses_main",
+            type: "tool",
+            tool: "bash",
+            state: { status: "running", input: { command: "bun test" } },
+          },
+        },
+      },
+      {
+        type: "message.part.updated",
+        properties: {
+          part: {
+            id: "tool-1",
+            sessionID: "ses_main",
+            type: "tool",
+            tool: "bash",
+            state: { status: "running", input: { command: "bun test" } },
+          },
+        },
+      },
+    ]
+
+    //#when
+    await processEvents(ctx, toAsyncIterable(events), state)
+
+    //#then
+    const rendered = stdoutSpy.mock.calls.map((call) => String(call[0] ?? "")).join("")
+    const headerCount = rendered.split("bun test").length - 1
+    expect(headerCount).toBe(1)
+    stdoutSpy.mockRestore()
+  })
+
+  it("renders tool header only once when both tool.execute and message.part.updated fire", async () => {
+    //#given
+    const ctx = createMockContext("ses_main")
+    const state = createEventState()
+    const stdoutSpy = spyOn(process.stdout, "write").mockImplementation(() => true)
+    const events: EventPayload[] = [
+      {
+        type: "tool.execute",
+        properties: {
+          sessionID: "ses_main",
+          name: "bash",
+          input: { command: "bun test" },
+        },
+      },
+      {
+        type: "message.part.updated",
+        properties: {
+          part: {
+            id: "tool-1",
+            sessionID: "ses_main",
+            type: "tool",
+            tool: "bash",
+            state: { status: "running", input: { command: "bun test" } },
+          },
+        },
+      },
+    ]
+
+    //#when
+    await processEvents(ctx, toAsyncIterable(events), state)
+
+    //#then
+    const rendered = stdoutSpy.mock.calls.map((call) => String(call[0] ?? "")).join("")
+    const headerCount = rendered.split("bun test").length - 1
+    expect(headerCount).toBe(1)
+    stdoutSpy.mockRestore()
+  })
+
+  it("renders tool output only once when both tool.result and message.part.updated(completed) fire", async () => {
+    //#given
+    const ctx = createMockContext("ses_main")
+    const state = createEventState()
+    const stdoutSpy = spyOn(process.stdout, "write").mockImplementation(() => true)
+    const events: EventPayload[] = [
+      {
+        type: "tool.execute",
+        properties: {
+          sessionID: "ses_main",
+          name: "bash",
+          input: { command: "bun test" },
+        },
+      },
+      {
+        type: "tool.result",
+        properties: {
+          sessionID: "ses_main",
+          name: "bash",
+          output: "UNIQUE-OUTPUT-MARKER",
+        },
+      },
+      {
+        type: "message.part.updated",
+        properties: {
+          part: {
+            id: "tool-1",
+            sessionID: "ses_main",
+            type: "tool",
+            tool: "bash",
+            state: { status: "completed", input: { command: "bun test" }, output: "UNIQUE-OUTPUT-MARKER" },
+          },
+        },
+      },
+    ]
+
+    //#when
+    await processEvents(ctx, toAsyncIterable(events), state)
+
+    //#then
+    const rendered = stdoutSpy.mock.calls.map((call) => String(call[0] ?? "")).join("")
+    const outputCount = rendered.split("UNIQUE-OUTPUT-MARKER").length - 1
+    expect(outputCount).toBe(1)
+    stdoutSpy.mockRestore()
+  })
+
+  it("does not re-render text when message.updated fires multiple times for same message", async () => {
+    //#given
+    const ctx = createMockContext("ses_main")
+    const state = createEventState()
+    const stdoutSpy = spyOn(process.stdout, "write").mockImplementation(() => true)
+    const events: EventPayload[] = [
+      {
+        type: "message.updated",
+        properties: {
+          info: { id: "msg_1", sessionID: "ses_main", role: "assistant", agent: "Sisyphus", modelID: "claude-opus-4-6" },
+        },
+      },
+      {
+        type: "message.part.delta",
+        properties: {
+          sessionID: "ses_main",
+          messageID: "msg_1",
+          field: "text",
+          delta: "Hello world",
+        },
+      },
+      {
+        type: "message.updated",
+        properties: {
+          info: { id: "msg_1", sessionID: "ses_main", role: "assistant", agent: "Sisyphus", modelID: "claude-opus-4-6" },
+        },
+      },
+      {
+        type: "message.part.updated",
+        properties: {
+          part: { id: "text-1", sessionID: "ses_main", type: "text", text: "Hello world" },
+        },
+      },
+    ]
+
+    //#when
+    await processEvents(ctx, toAsyncIterable(events), state)
+
+    //#then
+    const rendered = stdoutSpy.mock.calls.map((call) => String(call[0] ?? "")).join("")
+    const textCount = rendered.split("Hello world").length - 1
+    expect(textCount).toBe(1)
+    stdoutSpy.mockRestore()
+  })
 })