diff --git a/packages/adapter-utils/src/acpx-engine/execute.test.ts b/packages/adapter-utils/src/acpx-engine/execute.test.ts
index f661803383..324e20cf43 100644
--- a/packages/adapter-utils/src/acpx-engine/execute.test.ts
+++ b/packages/adapter-utils/src/acpx-engine/execute.test.ts
@@ -628,7 +628,7 @@ describe("shared ACPX engine runtime behavior", () => {
     });
   });
 
-  it("pins the existing summary and tool-event behavior when no engine knobs are set", async () => {
+  it("defaults run summaries to the final output segment without thought text", async () => {
     const root = await makeTempRoot();
     const stateDir = path.join(root, "state");
     const logs: Array<{ stream: string; text: string }> = [];
@@ -705,13 +705,9 @@ describe("shared ACPX engine runtime behavior", () => {
     } as never);
 
     expect(result.exitCode).toBe(0);
-    // The summary is the full concatenation of every text delta, thought
-    // stream included — the engine's long-standing behavior for claude,
-    // codex, gemini, and custom agents. If this assertion breaks, a change
-    // is altering summaries for existing adapters.
-    expect(result.summary).toBe(
-      "Let me get oriented and inspect the PRs…hidden chain of thought## Update\n\n- Checked PR status\n- Continue burn-in",
-    );
+    expect(result.summary).toBe("## Update\n\n- Checked PR status\n- Continue burn-in");
+    expect(result.summary).not.toContain("Let me get oriented");
+    expect(result.summary).not.toContain("hidden chain of thought");
     const toolCallEvents = logs
       .map((entry) => {
         try {
@@ -732,7 +728,7 @@ describe("shared ACPX engine runtime behavior", () => {
     ]);
   });
 
-  it("summarizes only the final output segment when the adapter sets summaryStrategy", async () => {
+  it("does not allow configuration to include thought text in run summaries", async () => {
     const root = await makeTempRoot();
     const stateDir = path.join(root, "state");
     const execute = createAcpxEngineExecutor({
@@ -803,7 +799,7 @@ describe("shared ACPX engine runtime behavior", () => {
         agent: "custom",
         agentCommand: "node ./fake-acp.js",
         stateDir,
-        summaryStrategy: "lastOutputSegment",
+        summaryStrategy: "full",
       },
       context: {},
       onLog: async () => {},
@@ -811,12 +807,74 @@ describe("shared ACPX engine runtime behavior", () => {
     } as never);
 
     expect(result.exitCode).toBe(0);
-    // Must not include intermediate narration or thought stream.
     expect(result.summary).toBe("## Update\n\n- Checked PR status\n- Continue burn-in");
     expect(result.summary).not.toContain("Let me get oriented");
     expect(result.summary).not.toContain("hidden chain of thought");
   });
 
+  it("treats a statusless initial tool call as an output-segment boundary", async () => {
+    const root = await makeTempRoot();
+    const stateDir = path.join(root, "state");
+    const execute = createAcpxEngineExecutor({
+      createRuntime: () => ({
+        ensureSession: async () => ({
+          backendSessionId: "backend-session",
+          agentSessionId: "agent-session",
+          runtimeSessionName: "runtime-session",
+        }),
+        startTurn: () => ({
+          events: (async function* () {
+            yield {
+              type: "text_delta",
+              text: "Intermediate setup that must not be published",
+              stream: "output",
+              tag: "agent_message_chunk",
+            };
+            yield {
+              type: "tool_call",
+              text: "Bash",
+              title: "Bash",
+              toolCallId: "tool-without-status",
+              tag: "tool_call",
+            };
+            yield {
+              type: "tool_call",
+              text: "Bash (completed)",
+              title: "Bash",
+              status: "completed",
+              toolCallId: "tool-without-status",
+              tag: "tool_call_update",
+            };
+            yield {
+              type: "text_delta",
+              text: "## Final update\n\n- Remediation verified",
+              stream: "output",
+              tag: "agent_message_chunk",
+            };
+            yield { type: "done", stopReason: "end_turn" };
+          })(),
+          result: Promise.resolve({ status: "completed", stopReason: "end_turn" }),
+          cancel: async () => {},
+        }),
+        close: async () => {},
+      }) as never,
+    });
+
+    const result = await execute({
+      runId: "run-summary-statusless-tool-call",
+      agent: { id: "agent-1", companyId: "company-1" },
+      runtime: {},
+      config: { agent: "custom", agentCommand: "node ./fake-acp.js", stateDir },
+      context: {},
+      onLog: async () => {},
+      onMeta: async () => {},
+    } as never);
+
+    expect(result.exitCode).toBe(0);
+    expect(result.summary).toBe("## Final update\n\n- Remediation verified");
+    expect(result.summary).not.toContain("Intermediate setup");
+  });
+
   it("buildAcpxRunSummary prefers the last non-empty segment", () => {
     expect(
       buildAcpxRunSummary({
diff --git a/packages/adapter-utils/src/acpx-engine/execute.ts b/packages/adapter-utils/src/acpx-engine/execute.ts
index fc3aa6ffd5..06ab95bb42 100644
--- a/packages/adapter-utils/src/acpx-engine/execute.ts
+++ b/packages/adapter-utils/src/acpx-engine/execute.ts
@@ -373,9 +373,6 @@ export interface AcpxEngineExecutorOptions {
 
 interface AcpxPreparedRuntime {
   acpxAgent: string;
-  // See the config parsing site: adapter-declared engine behavior knobs with
-  // behavior-preserving defaults.
-  summaryStrategy: "full" | "lastOutputSegment";
   coalescePlaceholderToolUpdates: boolean;
   mode: "persistent" | "oneshot";
   cwd: string;
@@ -1613,13 +1610,8 @@ async function buildRuntime(input: {
   );
 
   const acpxAgent = normalizeAgent(config);
-  // Engine behavior knobs set by the invoking adapter's acpx config builder
-  // (never by the engine itself): a verbose streaming backend opts into
-  // last-segment run summaries and placeholder tool-update coalescing here.
-  // The defaults preserve the engine's long-standing behavior, and the engine
-  // carries no knowledge of which adapters opt in.
-  const summaryStrategy: "full" | "lastOutputSegment" =
-    config.summaryStrategy === "lastOutputSegment" ? "lastOutputSegment" : "full";
+  // Run summaries always fail closed to the final output segment so internal
+  // thought text and intermediate narration cannot become issue comments.
   const coalescePlaceholderToolUpdates = config.coalescePlaceholderToolUpdates === true;
   const mode = normalizeMode(config);
   const permissionMode = normalizePermissionMode(config);
@@ -2175,7 +2167,6 @@ async function buildRuntime(input: {
 
   return {
     acpxAgent,
-    summaryStrategy,
     coalescePlaceholderToolUpdates,
     mode,
     // Remote runner-backed → the in-sandbox workspace dir; local / runner-less
@@ -2464,8 +2455,7 @@ async function emitAcpxLog(ctx: AdapterExecutionContext, payload: Record<string,
 
 /**
  * Build the short run summary that Paperclip may auto-post as an issue comment
- * when the agent leaves no comment of its own. Used only for agents whose
- * traits opt into the "lastOutputSegment" summary strategy.
+ * when the agent leaves no comment of its own.
  *
  * Prefer the last non-empty *output* segment after a tool call. Intermediate
  * "let me check…" narration between tools must not become a 50k-char dump.
@@ -3877,12 +3867,9 @@ export function createAcpxEngineExecutor(deps: AcpxEngineExecutorOptions = {}) {
       // controller and never rejects; it returns a `TurnCompletion`. The step
       // bodies below record the external result for the coordinator to reproduce.
       const runTurn = async (_ready: StartupReady): Promise<TurnCompletion> => {
-      // Summary accumulation, per the adapter-declared strategy. "full" (the
-      // default) collects every text delta exactly as before.
-      // "lastOutputSegment" collects output text only (never thought stream),
+      // Summary accumulation collects output text only (never thought stream),
       // segmented on tool starts so multi-step narration is not glued into one
-      // auto-comment dump.
-      const textParts: string[] = [];
+      // automatic comment dump.
       const outputSegments: string[] = [];
       let currentOutputChunk: string[] = [];
       const flushOutputSegment = () => {
@@ -3992,13 +3979,13 @@ export function createAcpxEngineExecutor(deps: AcpxEngineExecutorOptions = {}) {
         const turn = activeTurn as AcpRuntimeTurn;
         const toolTitles = new Map<string, string>();
         for await (const event of turn.events) {
-          if (event.type === "text_delta") {
-            if (prepared.summaryStrategy === "full") {
-              textParts.push(event.text);
-            } else if (event.stream !== "thought") {
-              currentOutputChunk.push(event.text);
-            }
-          } else if (event.type === "tool_call" && event.status === "pending") {
+          if (event.type === "text_delta" && event.stream !== "thought") {
+            currentOutputChunk.push(event.text);
+          } else if (event.type === "tool_call" && event.tag !== "tool_call_update") {
+            // ACP makes tool-call status optional. The normalized event tag is
+            // the reliable boundary between an initial call and its updates,
+            // so a statusless initial call must still end the preceding output
+            // segment while updates must not create extra boundaries.
             flushOutputSegment();
           }
           if (event.type === "status" && event.tag === "usage_update") {
@@ -4088,13 +4075,10 @@ export function createAcpxEngineExecutor(deps: AcpxEngineExecutorOptions = {}) {
               ? { cumulativeCostUsd: turnUsage.cumulativeCostUsd }
               : {}),
           },
-          summary:
-            prepared.summaryStrategy === "lastOutputSegment"
-              ? buildAcpxRunSummary({
-                  outputSegments,
-                  fallback: terminalStopReason || terminal.status,
-                })
-              : textParts.join("").trim() || terminalStopReason || terminal.status,
+          summary: buildAcpxRunSummary({
+            outputSegments,
+            fallback: terminalStopReason || terminal.status,
+          }),
           clearSession,
         };
         // The turn phase finished. A completed, non-timed-out turn is `ok`; every
diff --git a/server/src/__tests__/heartbeat-run-summary.test.ts b/server/src/__tests__/heartbeat-run-summary.test.ts
index 74051ab469..593c6006e0 100644
--- a/server/src/__tests__/heartbeat-run-summary.test.ts
+++ b/server/src/__tests__/heartbeat-run-summary.test.ts
@@ -133,6 +133,18 @@ describe("mergeHeartbeatRunResultJson", () => {
     expect(buildHeartbeatRunIssueComment(merged)).toBe("## Summary\n\n1. first thing\n2. second thing");
   });
 
+  it("posts only the final adapter summary when raw output contains intermediate narration", () => {
+    const merged = mergeHeartbeatRunResultJson(
+      { stdout: "Intermediate setup that must not be published" },
+      "## Final update\n\n- Remediation verified",
+    );
+
+    expect(buildHeartbeatRunIssueComment(merged)).toBe(
+      "## Final update\n\n- Remediation verified",
+    );
+    expect(buildHeartbeatRunIssueComment(merged)).not.toContain("Intermediate setup");
+  });
+
   it("creates a result payload when only a summary exists", () => {
     expect(mergeHeartbeatRunResultJson(null, "done")).toEqual({ summary: "done" });
   });