diff --git a/docs-site/src/content/docs/guides/providers.md b/docs-site/src/content/docs/guides/providers.md
index 901c75b242..94c006e724 100644
--- a/docs-site/src/content/docs/guides/providers.md
+++ b/docs-site/src/content/docs/guides/providers.md
@@ -771,7 +771,7 @@ OpenCodex provides official adapter support for Tencent Cloud's CodeBuddy Code C
   - Global: [CodeBuddy Global API Keys](https://www.codebuddy.ai/profile/keys)
   - CN: [CodeBuddy CN API Keys](https://copilot.tencent.com/profile/keys)
 - **Region Isolation:** `codebuddy` and `codebuddy-cn` use separate canonical endpoints (`https://www.codebuddy.ai` and `https://www.codebuddy.cn`) and isolated child environments (`CODEBUDDY_INTERNET_ENVIRONMENT=public` vs `internal`). Credentials are strictly region-scoped and never exchanged across environments. Overriding the canonical base URL fails closed.
-- **Tool Ownership:** In v1, the CLI is spawned with `--tools ""` and `--strict-mcp-config`, ensuring Codex maintains exclusive tool ownership. The provider operates in text and reasoning mode; client tool execution is not delegated to the vendor CLI.
+- **Tool Ownership:** In v1, the CLI is spawned with `--tools ""` and `--strict-mcp-config`, ensuring Codex maintains exclusive tool ownership. The provider operates in text and reasoning mode; client tool execution is not delegated to the vendor CLI. If the CLI writes an unquoted DSML `calls` control line followed by a `functions.*` invoke control line into text or reasoning, OpenCodex refuses the turn instead of forwarding the scaffold or interpreting it as an executable call. DSML discussed or quoted in prose, inline code, fenced code, or source examples remains ordinary answer text.
 - **Entitlements and Billing:** The provider uses the same vendor-documented CodeBuddy account/CLI authentication surface. Availability and billing of free, promotional, trial, or subscription credits remain determined by the user's CodeBuddy account entitlement.
 
 ### Official Qoder CLI (Global & CN)
diff --git a/src/adapters/codebuddy/adapter.ts b/src/adapters/codebuddy/adapter.ts
index 234e06907e..a769ac37da 100644
--- a/src/adapters/codebuddy/adapter.ts
+++ b/src/adapters/codebuddy/adapter.ts
@@ -4,6 +4,7 @@ import { mapReasoningEffort } from "../../reasoning-effort";
 import { buildSystemPrompt } from "../coding-agent/protocol";
 import { baseScopedEnv, runCodingAgentTurn, type CodingAgentDeps, type SpawnFn } from "../coding-agent/turn";
 import { CODEBUDDY_PROFILES, type CodeBuddyProfile } from "./profiles";
+import { guardCodeBuddyScaffolding } from "./scaffold-guard";
 
 export type { SpawnFn } from "../coding-agent/turn";
 export type CodeBuddyAdapterDeps = CodingAgentDeps;
@@ -75,7 +76,7 @@ export function createCodeBuddyAdapter(provider: OcxProviderConfig, deps: CodeBu
         provider,
         parsed,
         incoming,
-        emit,
+        emit: guardCodeBuddyScaffolding(emit),
         buildArgs: (resolved, req, prov) => buildArgs(resolved as CodeBuddyProfile, req, prov),
         buildEnv: (resolved, apiKey) => buildChildEnv(resolved as CodeBuddyProfile, apiKey),
         deps,
diff --git a/src/adapters/codebuddy/scaffold-guard.ts b/src/adapters/codebuddy/scaffold-guard.ts
new file mode 100644
index 0000000000..6f8c80aed5
--- /dev/null
+++ b/src/adapters/codebuddy/scaffold-guard.ts
@@ -0,0 +1,248 @@
+import type { AdapterEvent } from "../../types";
+
+/** Error code for a CodeBuddy turn whose output contains vendor agent scaffolding. */
+export const CODEBUDDY_SCAFFOLD_ERROR_CODE = "vendor_scaffold_detected";
+
+// The observed control protocol uses FULLWIDTH VERTICAL LINE (U+FF5C). Detection stays
+// deliberately narrower than the marker spelling: a calls control line must be followed by an
+// invoke line for a functions.* tool. That distinguishes an agent scaffold from prose quoting or
+// discussing one tag.
+const DSML_CALLS_LINE = "<｜｜dsml｜｜ calls>";
+const DSML_INVOKE_PREFIX = "<｜｜dsml｜｜ invoke name=\"functions.";
+
+export interface CodeBuddyScaffoldFilterResult {
+  /** Bytes released from a suffix withheld by an earlier event on this channel. */
+  releasedPending: string;
+  /** Safe bytes belonging to the event currently being processed. */
+  text: string;
+  /** The earlier pending event still owns the extended candidate. */
+  pendingContinues: boolean;
+  fail: boolean;
+}
+
+interface ScanResult {
+  safe: string;
+  held: string;
+  fail: boolean;
+  fence: "`" | "~" | null;
+  lineStart: boolean;
+}
+
+function prefixAtEnd(text: string, at: number, expected: string): boolean {
+  const rest = text.slice(at).toLowerCase();
+  return rest.length < expected.length && expected.startsWith(rest);
+}
+
+/**
+ * Scan complete bytes and retain only a bounded suffix that can still become a control sequence.
+ *
+ * Control tags are recognized only at column zero and outside fenced Markdown. Inline code,
+ * quoted strings, blockquotes, indented source, and prose all add syntax before the tag and are
+ * therefore forwarded unchanged. A calls line alone is harmless; refusal requires the observed
+ * two-line calls-plus-functions-invoke grammar.
+ */
+function scan(
+  text: string,
+  initialFence: "`" | "~" | null,
+  initialLineStart: boolean,
+): ScanResult {
+  let fence = initialFence;
+  let lineStart = initialLineStart;
+  let index = 0;
+
+  while (index < text.length) {
+    if (lineStart) {
+      const fenceMarkers = fence ? [fence.repeat(3)] : ["```", "~~~"];
+      const completeFence = fenceMarkers.find(marker => text.startsWith(marker, index));
+      if (completeFence) {
+        fence = fence ? null : (completeFence[0] as "`" | "~");
+        index += completeFence.length;
+        lineStart = false;
+        continue;
+      }
+      if (fenceMarkers.some(marker => prefixAtEnd(text, index, marker))) {
+        return { safe: text.slice(0, index), held: text.slice(index), fail: false, fence, lineStart };
+      }
+
+      if (!fence) {
+        const lowered = text.slice(index).toLowerCase();
+        if (lowered.startsWith(DSML_CALLS_LINE)) {
+          const afterCalls = index + DSML_CALLS_LINE.length;
+          let invokeAt = -1;
+          if (text[afterCalls] === "\n") invokeAt = afterCalls + 1;
+          else if (text[afterCalls] === "\r" && text[afterCalls + 1] === "\n") invokeAt = afterCalls + 2;
+          else if (afterCalls === text.length || (text[afterCalls] === "\r" && afterCalls + 1 === text.length)) {
+            return { safe: text.slice(0, index), held: text.slice(index), fail: false, fence, lineStart };
+          }
+
+          if (invokeAt >= 0) {
+            const invokeRest = text.slice(invokeAt).toLowerCase();
+            if (invokeRest.startsWith(DSML_INVOKE_PREFIX)) {
+              return { safe: text.slice(0, index), held: "", fail: true, fence, lineStart };
+            }
+            if (invokeRest.length === 0 || DSML_INVOKE_PREFIX.startsWith(invokeRest)) {
+              return { safe: text.slice(0, index), held: text.slice(index), fail: false, fence, lineStart };
+            }
+          }
+        } else if (prefixAtEnd(text, index, DSML_CALLS_LINE)) {
+          return { safe: text.slice(0, index), held: text.slice(index), fail: false, fence, lineStart };
+        }
+      }
+    }
+
+    const char = text[index]!;
+    index += 1;
+    lineStart = char === "\n";
+  }
+
+  return { safe: text, held: "", fail: false, fence, lineStart };
+}
+
+/** Streaming DSML control-sequence filter for one text or reasoning channel. */
+export class CodeBuddyScaffoldFilter {
+  private pending = "";
+  private failed = false;
+  private fence: "`" | "~" | null = null;
+  private lineStart = true;
+
+  /** True while an earlier event owns an unresolved marker or fence prefix. */
+  hasPending(): boolean {
+    return this.pending.length > 0;
+  }
+
+  push(chunk: string): CodeBuddyScaffoldFilterResult {
+    if (this.failed) {
+      return { releasedPending: "", text: "", pendingContinues: false, fail: false };
+    }
+    if (!chunk) {
+      return {
+        releasedPending: "",
+        text: "",
+        pendingContinues: this.hasPending(),
+        fail: false,
+      };
+    }
+
+    const priorPending = this.pending;
+    const result = scan(priorPending + chunk, this.fence, this.lineStart);
+    this.pending = result.held;
+    this.fence = result.fence;
+    this.lineStart = result.lineStart;
+    this.failed = result.fail;
+
+    const releasedLength = Math.min(priorPending.length, result.safe.length);
+    return {
+      releasedPending: result.safe.slice(0, releasedLength),
+      text: result.safe.slice(releasedLength),
+      pendingContinues: priorPending.length > 0 && result.safe.length === 0 && result.held.length > 0,
+      fail: result.fail,
+    };
+  }
+
+  /** Release a suffix that never completed the two-line control grammar. */
+  flush(): CodeBuddyScaffoldFilterResult {
+    if (this.failed) {
+      return { releasedPending: "", text: "", pendingContinues: false, fail: false };
+    }
+    const text = this.pending;
+    this.pending = "";
+    return { releasedPending: text, text: "", pendingContinues: false, fail: false };
+  }
+}
+
+function codeBuddyScaffoldErrorMessage(): string {
+  return "CodeBuddy CLI emitted vendor tool-call markup in an assistant output channel. This route"
+    + " runs the CLI with its own tools and MCP servers disabled and Codex owns tool control, so"
+    + " the turn was refused rather than forwarding or executing vendor agent scaffolding.";
+}
+
+/** Guard both streamed channels while preserving event order around withheld marker prefixes. */
+export function guardCodeBuddyScaffolding(emit: (event: AdapterEvent) => void): (event: AdapterEvent) => void {
+  const textFilter = new CodeBuddyScaffoldFilter();
+  const thinkingFilter = new CodeBuddyScaffoldFilter();
+  type PendingChannel = "text" | "thinking";
+  type EventSlot = { resolved: boolean; event?: AdapterEvent };
+  const eventQueue: EventSlot[] = [];
+  const pendingSlots = new Map<PendingChannel, EventSlot>();
+  let closed = false;
+
+  const channelEvent = (channel: PendingChannel, text: string): AdapterEvent => channel === "text"
+    ? { type: "text_delta", text }
+    : { type: "thinking_delta", thinking: text };
+
+  const drainResolved = (): void => {
+    while (eventQueue[0]?.resolved) {
+      const slot = eventQueue.shift()!;
+      if (slot.event) emit(slot.event);
+    }
+  };
+
+  const enqueueResolved = (event: AdapterEvent): void => {
+    eventQueue.push({ resolved: true, event });
+    drainResolved();
+  };
+
+  const resolvePendingSlot = (channel: PendingChannel, text: string): void => {
+    const slot = pendingSlots.get(channel);
+    if (!slot) return;
+    slot.resolved = true;
+    if (text) slot.event = channelEvent(channel, text);
+    pendingSlots.delete(channel);
+    drainResolved();
+  };
+
+  const enqueuePendingSlot = (channel: PendingChannel): void => {
+    const slot: EventSlot = { resolved: false };
+    eventQueue.push(slot);
+    pendingSlots.set(channel, slot);
+  };
+
+  const flushAllPending = (): void => {
+    for (const channel of ["text", "thinking"] as const) {
+      if (!pendingSlots.has(channel)) continue;
+      const filter = channel === "text" ? textFilter : thinkingFilter;
+      resolvePendingSlot(channel, filter.flush().releasedPending);
+    }
+    drainResolved();
+  };
+
+  const refuse = (): void => {
+    if (closed) return;
+    flushAllPending();
+    closed = true;
+    emit({
+      type: "error",
+      message: codeBuddyScaffoldErrorMessage(),
+      status: 502,
+      errorType: "upstream_error",
+      code: CODEBUDDY_SCAFFOLD_ERROR_CODE,
+      retryable: false,
+    });
+  };
+
+  return (event: AdapterEvent): void => {
+    if (closed) return;
+    if (event.type === "text_delta" || event.type === "thinking_delta") {
+      const channel: PendingChannel = event.type === "text_delta" ? "text" : "thinking";
+      const filter = channel === "text" ? textFilter : thinkingFilter;
+      const hadPending = filter.hasPending();
+      const cleaned = filter.push(event.type === "text_delta" ? event.text : event.thinking);
+      if (hadPending && !cleaned.pendingContinues) resolvePendingSlot(channel, cleaned.releasedPending);
+      if (cleaned.text) {
+        enqueueResolved(event.type === "text_delta"
+          ? { ...event, text: cleaned.text }
+          : { ...event, thinking: cleaned.text });
+      }
+      if (filter.hasPending() && !cleaned.pendingContinues) enqueuePendingSlot(channel);
+      if (cleaned.fail) refuse();
+      return;
+    }
+    if (event.type === "done" || event.type === "error" || event.type === "incomplete") {
+      flushAllPending();
+      closed = true;
+      emit(event);
+      return;
+    }
+    enqueueResolved(event);
+  };
+}
diff --git a/structure/providers/chat-compat.md b/structure/providers/chat-compat.md
index 746d3de817..381276d04b 100644
--- a/structure/providers/chat-compat.md
+++ b/structure/providers/chat-compat.md
@@ -354,7 +354,11 @@ The shared coding-agent projection (CodeBuddy, Qoder) carries tool-result images
 real image blocks rather than flattening them to the text `[image]`, and orders image
 blocks chronologically — history before current — so attachment order matches the
 prose the model reads beside them. Vendor tool execution stays disabled on both
-adapters, and Qoder's explicit refusal of original images is unchanged.
+adapters. CodeBuddy refuses an unquoted, line-oriented full-width-bar DSML `calls`
+container followed by a `functions.*` invoke control line in either output channel; it
+preserves preceding answer text, never promotes vendor prose into execution authority,
+and leaves discussed or quoted literals and code examples untouched. Qoder's explicit
+refusal of original images is unchanged.
 
 Canonical Responses identity sanitation and narrowly scoped pre-output combo recovery follow [request-local target compatibility](../runtime.md#request-local-target-compatibility); other adapter contracts remain unchanged.
 
diff --git a/tests/providers/codebuddy-adapter.test.ts b/tests/providers/codebuddy-adapter.test.ts
index 0da898ea82..76caabfae9 100644
--- a/tests/providers/codebuddy-adapter.test.ts
+++ b/tests/providers/codebuddy-adapter.test.ts
@@ -3,6 +3,7 @@ import { EventEmitter } from "node:events";
 import { Readable, Writable } from "node:stream";
 import type { ChildProcess } from "node:child_process";
 import { buildArgs, buildChildEnv, createCodeBuddyAdapter, type SpawnFn } from "../../src/adapters/codebuddy/adapter";
+import { guardCodeBuddyScaffolding } from "../../src/adapters/codebuddy/scaffold-guard";
 import { CODEBUDDY_CN_PROFILE, CODEBUDDY_GLOBAL_PROFILE, clearCodeBuddyBinaryCache } from "../../src/adapters/codebuddy/profiles";
 import type { AdapterEvent, OcxParsedRequest, OcxProviderConfig } from "../../src/types";
 import { createTestTranslatorBudget } from "../helpers/translator-budget";
@@ -221,6 +222,236 @@ describe("codebuddy runTurn streams a headless turn", () => {
     expect(child.written.join("")).toContain('"text":"hello"');
   });
 
+  test("refuses a full-message DSML calls-and-invoke scaffold", async () => {
+    const leaked = "I'll inspect it.\n<｜｜DSML｜｜ calls>\n"
+      + "<｜｜DSML｜｜ invoke name=\"functions.exec\">\nsecret-command";
+    const stdout = [
+      enc.encode(`${JSON.stringify({
+        type: "assistant",
+        message: { role: "assistant", content: [{ type: "text", text: leaked }] },
+      })}\n`),
+      enc.encode('{"type":"result","subtype":"success","is_error":false}\n'),
+    ];
+    const adapter = createCodeBuddyAdapter(provider(), {
+      spawn: () => fakeChild(stdout) as unknown as ChildProcess,
+      which: () => "/usr/bin/codebuddy",
+      killGraceMs: 20,
+    });
+
+    const events = await run(adapter, parsed());
+    expect(events.filter(event => event.type === "text_delta"))
+      .toEqual([{ type: "text_delta", text: "I'll inspect it.\n" }]);
+    expect(events.some(event => event.type === "done")).toBe(false);
+    expect(events.at(-1)).toMatchObject({
+      type: "error",
+      code: "vendor_scaffold_detected",
+      retryable: false,
+      status: 502,
+    });
+    expect(JSON.stringify(events)).not.toContain("secret-command");
+  });
+
+  test("detects a DSML control sequence split across streamed text deltas", async () => {
+    const frame = (text: string) => `${JSON.stringify({
+      type: "stream_event",
+      event: { type: "content_block_delta", delta: { type: "text_delta", text } },
+    })}\n`;
+    const stdout = [
+      enc.encode(frame("Safe prefix.\n<｜｜DS")),
+      enc.encode(frame("ML｜｜ calls>\n<｜｜DSML｜｜ invoke name=\"funct")),
+      enc.encode(frame("ions.exec\">private-body")),
+      enc.encode('{"type":"result","subtype":"success","is_error":false}\n'),
+    ];
+    const adapter = createCodeBuddyAdapter(provider(), {
+      spawn: () => fakeChild(stdout) as unknown as ChildProcess,
+      which: () => "/usr/bin/codebuddy",
+      killGraceMs: 20,
+    });
+
+    const events = await run(adapter, parsed());
+    expect(events.filter(event => event.type === "text_delta"))
+      .toEqual([{ type: "text_delta", text: "Safe prefix.\n" }]);
+    expect(events.at(-1)).toMatchObject({ type: "error", code: "vendor_scaffold_detected" });
+    expect(events.some(event => event.type === "done")).toBe(false);
+    expect(JSON.stringify(events)).not.toContain("private-body");
+  });
+
+  test("refuses DSML calls-and-invoke scaffolding from reasoning independently", async () => {
+    const stdout = [
+      enc.encode(`${JSON.stringify({
+        type: "stream_event",
+        event: {
+          type: "content_block_delta",
+          delta: {
+            type: "thinking_delta",
+            thinking: "Safe thought.\n<｜｜DSML｜｜ calls>\n"
+              + "<｜｜DSML｜｜ invoke name=\"functions.exec\">private-body",
+          },
+        },
+      })}\n`),
+      enc.encode('{"type":"result","subtype":"success","is_error":false}\n'),
+    ];
+    const adapter = createCodeBuddyAdapter(provider(), {
+      spawn: () => fakeChild(stdout) as unknown as ChildProcess,
+      which: () => "/usr/bin/codebuddy",
+      killGraceMs: 20,
+    });
+
+    const events = await run(adapter, parsed());
+    expect(events.filter(event => event.type === "thinking_delta"))
+      .toEqual([{ type: "thinking_delta", thinking: "Safe thought.\n" }]);
+    expect(events.at(-1)).toMatchObject({
+      type: "error",
+      code: "vendor_scaffold_detected",
+      retryable: false,
+    });
+    expect(events.some(event => event.type === "done")).toBe(false);
+    expect(JSON.stringify(events)).not.toContain("private-body");
+  });
+
+  test("delivers a lone discussed DSML calls tag unchanged", () => {
+    const events: AdapterEvent[] = [];
+    const guarded = guardCodeBuddyScaffolding(event => events.push(event));
+    const answer = "The string <｜｜DSML｜｜ calls> names the calls container.";
+
+    guarded({ type: "text_delta", text: answer });
+    guarded({ type: "done", stopReason: "stop" });
+
+    expect(events).toEqual([
+      { type: "text_delta", text: answer },
+      { type: "done", stopReason: "stop" },
+    ]);
+  });
+
+  test("delivers quoted and inline-code DSML literals unchanged", () => {
+    const events: AdapterEvent[] = [];
+    const guarded = guardCodeBuddyScaffolding(event => events.push(event));
+    const answer = "\"<｜｜DSML｜｜ calls>\"\n"
+      + "\"<｜｜DSML｜｜ invoke name=\\\"functions.exec\\\">\"\n"
+      + "Use `<｜｜DSML｜｜ calls>` when discussing the literal.\n"
+      + "> <｜｜DSML｜｜ calls>\n> <｜｜DSML｜｜ invoke name=\"functions.exec\">";
+
+    guarded({ type: "text_delta", text: answer });
+    guarded({ type: "done", stopReason: "stop" });
+
+    expect(events).toEqual([
+      { type: "text_delta", text: answer },
+      { type: "done", stopReason: "stop" },
+    ]);
+  });
+
+  test("delivers a fenced DSML source example unchanged across deltas", () => {
+    const events: AdapterEvent[] = [];
+    const guarded = guardCodeBuddyScaffolding(event => events.push(event));
+    const first = "```text\n<｜｜DSML｜｜ calls>\n";
+    const second = "<｜｜DSML｜｜ invoke name=\"functions.exec\">\n```";
+
+    guarded({ type: "text_delta", text: first });
+    guarded({ type: "text_delta", text: second });
+    guarded({ type: "done", stopReason: "stop" });
+
+    expect(events).toEqual([
+      { type: "text_delta", text: first },
+      { type: "text_delta", text: second },
+      { type: "done", stopReason: "stop" },
+    ]);
+  });
+
+  test("delivers source strings containing both DSML literals unchanged", () => {
+    const events: AdapterEvent[] = [];
+    const guarded = guardCodeBuddyScaffolding(event => events.push(event));
+    const answer = "const calls = '<｜｜DSML｜｜ calls>';\n"
+      + "const invoke = '<｜｜DSML｜｜ invoke name=\"functions.exec\">';";
+
+    guarded({ type: "text_delta", text: answer });
+    guarded({ type: "done", stopReason: "stop" });
+
+    expect(events).toEqual([
+      { type: "text_delta", text: answer },
+      { type: "done", stopReason: "stop" },
+    ]);
+  });
+
+  test("delivers an unquoted invoke line when no calls container precedes it", () => {
+    const events: AdapterEvent[] = [];
+    const guarded = guardCodeBuddyScaffolding(event => events.push(event));
+    const answer = "<｜｜DSML｜｜ invoke name=\"functions.exec\">";
+
+    guarded({ type: "text_delta", text: answer });
+    guarded({ type: "done", stopReason: "stop" });
+
+    expect(events).toEqual([
+      { type: "text_delta", text: answer },
+      { type: "done", stopReason: "stop" },
+    ]);
+  });
+
+  test("releases a lone control-line candidate at the terminal", () => {
+    const events: AdapterEvent[] = [];
+    const guarded = guardCodeBuddyScaffolding(event => events.push(event));
+
+    guarded({ type: "text_delta", text: "<｜｜DSML｜｜ calls>" });
+    expect(events).toEqual([]);
+    guarded({ type: "done", stopReason: "stop" });
+
+    expect(events).toEqual([
+      { type: "text_delta", text: "<｜｜DSML｜｜ calls>" },
+      { type: "done", stopReason: "stop" },
+    ]);
+  });
+
+  test("queues later events behind an unresolved marker prefix", () => {
+    const events: AdapterEvent[] = [];
+    const guarded = guardCodeBuddyScaffolding(event => events.push(event));
+
+    guarded({ type: "thinking_delta", thinking: "<" });
+    guarded({ type: "text_delta", text: "Hello" });
+    guarded({ type: "tool_call_start", id: "call_1", name: "exec" });
+    expect(events).toEqual([]);
+    guarded({ type: "done", stopReason: "stop" });
+
+    expect(events).toEqual([
+      { type: "thinking_delta", thinking: "<" },
+      { type: "text_delta", text: "Hello" },
+      { type: "tool_call_start", id: "call_1", name: "exec" },
+      { type: "done", stopReason: "stop" },
+    ]);
+  });
+
+  test("keeps an existing pending slot when its channel receives an empty delta", () => {
+    const events: AdapterEvent[] = [];
+    const guarded = guardCodeBuddyScaffolding(event => events.push(event));
+
+    guarded({ type: "thinking_delta", thinking: "<" });
+    guarded({ type: "text_delta", text: "Hello" });
+    guarded({ type: "thinking_delta", thinking: "" });
+    guarded({ type: "done", stopReason: "stop" });
+
+    expect(events).toEqual([
+      { type: "thinking_delta", thinking: "<" },
+      { type: "text_delta", text: "Hello" },
+      { type: "done", stopReason: "stop" },
+    ]);
+  });
+
+  test("moves a replaced pending marker prefix to its new arrival position", () => {
+    const events: AdapterEvent[] = [];
+    const guarded = guardCodeBuddyScaffolding(event => events.push(event));
+
+    guarded({ type: "thinking_delta", thinking: "<" });
+    guarded({ type: "text_delta", text: "<" });
+    guarded({ type: "thinking_delta", thinking: "not marker\n<" });
+    guarded({ type: "done", stopReason: "stop" });
+
+    expect(events).toEqual([
+      { type: "thinking_delta", thinking: "<" },
+      { type: "text_delta", text: "<" },
+      { type: "thinking_delta", thinking: "not marker\n" },
+      { type: "thinking_delta", thinking: "<" },
+      { type: "done", stopReason: "stop" },
+    ]);
+  });
+
   test("region isolation: the global adapter never spawns with the CN environment", async () => {
     let seenEnv: NodeJS.ProcessEnv | undefined;
     const spawn: SpawnFn = (_cmd, _args, opts) => { seenEnv = opts.env as NodeJS.ProcessEnv; return fakeChild([enc.encode('{"type":"result","subtype":"success"}\n')]) as unknown as ChildProcess; };