diff --git a/app/test/e2e/specs/chat-harness-subagent-continue.spec.ts b/app/test/e2e/specs/chat-harness-subagent-continue.spec.ts
index 329082b08c..a030b077fa 100644
--- a/app/test/e2e/specs/chat-harness-subagent-continue.spec.ts
+++ b/app/test/e2e/specs/chat-harness-subagent-continue.spec.ts
@@ -7,17 +7,34 @@
  *   3. The harness exits early, returns [SUBAGENT_AWAITING_USER] to the
  *      orchestrator.
  *   4. Orchestrator surfaces the question to the user.
- *   5. User replies in the composer ("the main repo").
+ *   5. User replies in the composer.
  *   6. Orchestrator calls `continue_subagent` with the user's answer.
  *   7. Researcher resumes from checkpoint, produces final answer.
  *   8. Orchestrator produces final synthesis with canary.
  *
+ * Scripting: `llmKeywordRules` + mock `{{DYNAMIC_*}}` template substitution.
+ * A prior version used `llmForcedResponses` but that FIFO drains one entry
+ * per `/chat/completions` call regardless of who called; the researcher's
+ * own harness loop plus any ancillary summarisation/memory-prep call
+ * shifts responses out of order and the scripted final canary lands on
+ * the wrong turn or never renders (tinyhumansai/openhuman#4517). Keyword
+ * rules route each call by a substring of its latest user/tool message
+ * and are never consumed.
+ *
+ * The orchestrator's `continue_subagent` call needs a real `task_id`
+ * (`sub-<uuid>` generated at delegate time in
+ * `src/openhuman/agent_orchestration/tools/dispatch.rs`). Tests can't
+ * know it ahead of time, so the mock substitutes `{{DYNAMIC_TASK_ID}}` /
+ * `{{DYNAMIC_AGENT_ID}}` from the latest `[SUBAGENT_AWAITING_USER]`
+ * envelope in the message history (see
+ * `scripts/mock-api/routes/llm/shared.mjs::renderDynamicPlaceholders`).
+ *
  * Verifies:
  *   - The tool timeline shows a subagent entry.
  *   - The final canary text renders in the DOM.
  *   - The mock LLM received ≥4 POST requests (orchestrator initial +
- *     researcher initial + orchestrator relay + researcher resumed +
- *     orchestrator final).
+ *     researcher initial + orchestrator relay + orchestrator continue +
+ *     researcher resumed + orchestrator final).
  *   - Persisted thread JSONL contains the final canary text.
  */
 import { waitForApp } from '../helpers/app-helpers';
@@ -37,33 +54,66 @@ import { navigateViaHash } from '../helpers/shared-flows';
 import { getRequestLog, setMockBehavior, startMockServer, stopMockServer } from '../mock-server';
 
 const USER_ID = 'e2e-chat-harness-subagent-continue';
-const PROMPT = 'Research the answer and tell me a marker phrase.';
+// Per-turn probes carry disjoint distinctive tokens so `pickProbeText`'s
+// substring match routes each of the six model calls to exactly one rule
+// regardless of any ancillary summarisation / title-gen calls the harness may
+// issue on top of the happy-path turns.
+const PROMPT =
+  'Please delegate a research task with the chromatophore-request badge and return a marker phrase.';
+const DELEGATE_PROMPT = 'Return the harlequin-token phrase after searching.';
+const CLARIFICATION_QUESTION = 'Which repo should I search for the citrine-cliff badge?';
+const USER_ANSWER = 'Please try the wisteria-tag project.';
+const RESEARCHER_FINAL_REPLY = 'In the wisteria-tag project I found the zenith-beacon marker.';
 const CANARY_FINAL = 'subagent-continue-canary-9bc3f';
-const CLARIFICATION_QUESTION = 'Which repo should I search?';
-const USER_ANSWER = 'the main repo';
-const RESEARCHER_FINAL_REPLY = 'After searching the main repo, the answer is 42.';
-
-// Five forced responses, popped in order by the mock LLM streamer:
-// 1. Orchestrator: emits `research` tool call.
-// 2. Researcher: calls `ask_user_clarification` (triggers early exit).
-// 3. Orchestrator: sees [SUBAGENT_AWAITING_USER], asks user the question.
-// 4. Orchestrator (after user reply): calls `continue_subagent` with user's answer.
-// 5. Researcher (resumed): produces final text answer.
-// 6. Orchestrator: final synthesis containing the canary.
-const FORCED_RESPONSES = [
-  // 1. Orchestrator: delegate to researcher.
+
+// Content-addressed keyword rules — never depleted, immune to extra
+// ancillary /chat/completions calls (#4517).
+//
+// ORDER MATTERS: the researcher's resumed probe includes both the framing
+// `[User's answer to your clarification question]` prepended by
+// `src/openhuman/agent_orchestration/tools/continue_subagent.rs` AND the raw
+// user answer text (`wisteria-tag`). Its rule must appear BEFORE the
+// orchestrator-continue rule (keyed on `wisteria-tag`) so the researcher's
+// resumed call hits the researcher rule first.
+const KEYWORD_RULES = [
+  // Researcher's resumed turn — the harness reconstructs history and appends
+  // "[User's answer to your clarification question]\n<message>" as a user
+  // message (continue_subagent.rs). Key on the framing so this rule only
+  // matches the researcher, not the orchestrator's own continue turn (which
+  // sees the composer message without framing).
+  { keyword: "user's answer to your clarification question", content: RESEARCHER_FINAL_REPLY },
+  // Orchestrator's final synthesis — probe is the tool result carrying the
+  // researcher's resumed output. `zenith-beacon` is unique to that reply.
+  { keyword: 'zenith-beacon', content: `Done. The result is: ${CANARY_FINAL}` },
+  // Orchestrator's continue_subagent turn — user answered the clarification
+  // in the composer; the latest user message is USER_ANSWER. The mock
+  // substitutes `{{DYNAMIC_TASK_ID}}` / `{{DYNAMIC_AGENT_ID}}` from the
+  // preceding `[SUBAGENT_AWAITING_USER]` envelope in message history so the
+  // resulting tool_call carries the real runtime-generated task_id.
   {
+    keyword: 'wisteria-tag',
     content: '',
     toolCalls: [
       {
-        id: 'call_research_1',
-        name: 'research',
-        arguments: JSON.stringify({ prompt: 'Tell me a marker phrase' }),
+        id: 'call_continue_1',
+        name: 'continue_subagent',
+        arguments: JSON.stringify({
+          task_id: '{{DYNAMIC_TASK_ID}}',
+          agent_id: '{{DYNAMIC_AGENT_ID}}',
+          message: USER_ANSWER,
+        }),
       },
     ],
   },
-  // 2. Researcher: ask clarification (tool call).
+  // Orchestrator's relay turn — probe is the `[SUBAGENT_AWAITING_USER]`
+  // envelope; `citrine-cliff` is embedded in the clarification question and
+  // does not appear in any later probe.
+  { keyword: 'citrine-cliff', content: `The researcher needs to know: ${CLARIFICATION_QUESTION}` },
+  // Researcher's initial turn — dispatch renders "Task:\n<DELEGATE_PROMPT>"
+  // (archetype_delegation.rs render_structured_handoff) so `harlequin-token`
+  // is unique to the researcher's incoming user message.
   {
+    keyword: 'harlequin-token',
     content: '',
     toolCalls: [
       {
@@ -73,27 +123,22 @@ const FORCED_RESPONSES = [
       },
     ],
   },
-  // 3. Orchestrator: relay the question to the user.
-  { content: `The researcher needs to know: ${CLARIFICATION_QUESTION}` },
-  // 4. Orchestrator (after user replies): continue_subagent.
+  // Orchestrator's initial turn — user PROMPT. Shared with the fire-and-forget
+  // title-gen call (threadSlice.ts, tools: None) which sees the same probe;
+  // `chat_with_system` consumes `content` and ignores unexpected tool_calls,
+  // so a delegation-triggering rule here is safe for both callers (benign
+  // "Delegating to researcher." title).
   {
-    content: '',
+    keyword: 'chromatophore-request',
+    content: 'Delegating to researcher.',
     toolCalls: [
       {
-        id: 'call_continue_1',
-        name: 'continue_subagent',
-        arguments: JSON.stringify({
-          task_id: '{{DYNAMIC_TASK_ID}}',
-          agent_id: 'researcher',
-          message: USER_ANSWER,
-        }),
+        id: 'call_research_1',
+        name: 'research',
+        arguments: JSON.stringify({ prompt: DELEGATE_PROMPT }),
       },
     ],
   },
-  // 5. Researcher (resumed): final answer.
-  { content: RESEARCHER_FINAL_REPLY },
-  // 6. Orchestrator: final synthesis.
-  { content: `Done. The result is: ${CANARY_FINAL}` },
 ];
 
 interface RuntimeSnapshot {
@@ -132,12 +177,12 @@ describe('Chat harness — orchestrator → subagent continuation flow', () => {
     await waitForApp();
     await resetApp(USER_ID);
 
-    setMockBehavior('llmForcedResponses', JSON.stringify(FORCED_RESPONSES));
+    setMockBehavior('llmKeywordRules', JSON.stringify(KEYWORD_RULES));
     setMockBehavior('llmStreamChunkDelayMs', '10');
   });
 
   after(async () => {
-    setMockBehavior('llmForcedResponses', '');
+    setMockBehavior('llmKeywordRules', '');
     setMockBehavior('llmStreamChunkDelayMs', '');
     await stopMockServer();
   });
@@ -226,9 +271,9 @@ describe('Chat harness — orchestrator → subagent continuation flow', () => {
     const llmHits = log.filter(
       r => r.method === 'POST' && r.url.includes('/openai/v1/chat/completions')
     );
-    // Orchestrator turn 1 + researcher turn + orchestrator turn 2 (relay question)
-    // + orchestrator turn 3 (continue) + researcher turn 2 + orchestrator turn 4 (synthesis)
-    // = 6, but accept ≥4 for robustness.
+    // Orchestrator turn 1 + researcher turn 1 + orchestrator relay
+    // + orchestrator continue + researcher resumed + orchestrator final
+    // = 6, but accept ≥4 for robustness against harness optimisations.
     expect(llmHits.length).toBeGreaterThanOrEqual(4);
   });
 
diff --git a/scripts/mock-api/routes/__tests__/llm.test.mjs b/scripts/mock-api/routes/__tests__/llm.test.mjs
index f6c8e4058b..01e6af3be9 100644
--- a/scripts/mock-api/routes/__tests__/llm.test.mjs
+++ b/scripts/mock-api/routes/__tests__/llm.test.mjs
@@ -3,6 +3,10 @@ import assert from "node:assert/strict";
 
 import { handleLlmCompletions } from "../llm.mjs";
 import { handleIntegrations } from "../integrations.mjs";
+import {
+  applyDynamicPlaceholdersToResponse,
+  renderDynamicPlaceholders,
+} from "../llm/shared.mjs";
 import {
   listMockLlmThreads,
   resetMockBehavior,
@@ -339,3 +343,195 @@ test("records thread state for multi-turn mock LLM sessions", () => {
   assert.equal(thread.lastFamily, "summarization");
   assert.equal(thread.turnCount, 1);
 });
+
+// ── {{DYNAMIC_*}} placeholder substitution (#4517) ──────────────────
+//
+// Envelope shape matches awaiting_user_envelope() in
+// src/openhuman/agent_orchestration/tools/awaiting_user.rs — the parser
+// must handle the exact production format (JSON-encoded question,
+// `worker_thread_id: (none)`, trailing instruction block).
+function subagentAwaitingUserEnvelope({
+  taskId = "sub-abc123-fake-uuid",
+  agentId = "researcher",
+  workerThreadId = "(none)",
+  question = "Which repo should I search?",
+} = {}) {
+  return `[SUBAGENT_AWAITING_USER]
+task_id: ${taskId}
+agent_id: ${agentId}
+worker_thread_id: ${workerThreadId}
+question: ${JSON.stringify(question)}
+[/SUBAGENT_AWAITING_USER]
+
+The sub-agent needs clarification before it can continue. Surface the above question to the user. When the user responds, call continue_subagent with the task_id, agent_id, and the user's answer as the message parameter.`;
+}
+
+test("renderDynamicPlaceholders substitutes task_id and agent_id from history", () => {
+  const parsedBody = {
+    messages: [
+      { role: "user", content: "please research the codex marker" },
+      {
+        role: "tool",
+        content: subagentAwaitingUserEnvelope({
+          taskId: "sub-runtime-42",
+          agentId: "researcher",
+        }),
+      },
+      { role: "user", content: "the main repo" },
+    ],
+  };
+  const rendered = renderDynamicPlaceholders(
+    '{"task_id":"{{DYNAMIC_TASK_ID}}","agent_id":"{{DYNAMIC_AGENT_ID}}","message":"the main repo"}',
+    parsedBody,
+  );
+  assert.equal(
+    rendered,
+    '{"task_id":"sub-runtime-42","agent_id":"researcher","message":"the main repo"}',
+  );
+});
+
+test("renderDynamicPlaceholders returns input unchanged when no envelope present", () => {
+  const parsedBody = {
+    messages: [{ role: "user", content: "no envelope here" }],
+  };
+  assert.equal(
+    renderDynamicPlaceholders("{{DYNAMIC_TASK_ID}}", parsedBody),
+    "{{DYNAMIC_TASK_ID}}",
+  );
+});
+
+test("renderDynamicPlaceholders short-circuits when text has no placeholders", () => {
+  // Guardrail: no envelope scan for content without placeholders.
+  assert.equal(renderDynamicPlaceholders("plain text", null), "plain text");
+});
+
+test("applyDynamicPlaceholdersToResponse renders content and toolCalls arguments without mutating input", () => {
+  const parsedBody = {
+    messages: [
+      {
+        role: "tool",
+        content: subagentAwaitingUserEnvelope({ taskId: "sub-xyz" }),
+      },
+    ],
+  };
+  const original = {
+    content: "prefix {{DYNAMIC_TASK_ID}}",
+    toolCalls: [
+      {
+        id: "call_1",
+        name: "continue_subagent",
+        arguments: '{"task_id":"{{DYNAMIC_TASK_ID}}"}',
+      },
+    ],
+  };
+  const rendered = applyDynamicPlaceholdersToResponse(original, parsedBody);
+  assert.equal(rendered.content, "prefix sub-xyz");
+  assert.equal(rendered.toolCalls[0].arguments, '{"task_id":"sub-xyz"}');
+  // Purity: input must not be mutated (call sites re-read the rule on the
+  // next request; mutation would let a first substitution leak into later
+  // turns that don't have an envelope).
+  assert.equal(original.content, "prefix {{DYNAMIC_TASK_ID}}");
+  assert.equal(
+    original.toolCalls[0].arguments,
+    '{"task_id":"{{DYNAMIC_TASK_ID}}"}',
+  );
+});
+
+test("llmKeywordRules substitute {{DYNAMIC_TASK_ID}} in continue_subagent tool_call args", () => {
+  setMockBehaviors(
+    {
+      llmKeywordRules: JSON.stringify([
+        {
+          keyword: "user answer",
+          content: "",
+          toolCalls: [
+            {
+              id: "call_continue_1",
+              name: "continue_subagent",
+              arguments: JSON.stringify({
+                task_id: "{{DYNAMIC_TASK_ID}}",
+                agent_id: "{{DYNAMIC_AGENT_ID}}",
+                message: "the main repo",
+              }),
+            },
+          ],
+        },
+      ]),
+    },
+    "replace",
+  );
+
+  const ctx = makeCtx({
+    parsedBody: {
+      model: "e2e-mock-model",
+      // No tools → not a "primary turn" for the forced-response FIFO, but
+      // keyword rules still fire and this validates the substitution site.
+      messages: [
+        {
+          role: "tool",
+          content: subagentAwaitingUserEnvelope({
+            taskId: "sub-realtime-777",
+            agentId: "researcher",
+          }),
+        },
+        { role: "user", content: "here is my user answer" },
+      ],
+    },
+  });
+
+  assert.equal(handleLlmCompletions(ctx), true);
+  const body = JSON.parse(ctx.res.body);
+  const args = body.choices[0].message.tool_calls[0].function.arguments;
+  const parsed = JSON.parse(args);
+  assert.equal(parsed.task_id, "sub-realtime-777");
+  assert.equal(parsed.agent_id, "researcher");
+  assert.equal(parsed.message, "the main repo");
+  // Placeholder text must be fully consumed.
+  assert.ok(!args.includes("{{DYNAMIC_"), `args should not contain unresolved placeholders: ${args}`);
+});
+
+test("llmKeywordRules leave the rule unmutated across successive requests", () => {
+  // Regression guard for applyDynamicPlaceholdersToResponse purity: two
+  // requests, only the first has an envelope in history. Second must still
+  // see the raw `{{DYNAMIC_TASK_ID}}` (which then falls through unchanged
+  // since there is no envelope to substitute from).
+  setMockBehaviors(
+    {
+      llmKeywordRules: JSON.stringify([
+        {
+          keyword: "answer",
+          content: "raw {{DYNAMIC_TASK_ID}}",
+        },
+      ]),
+    },
+    "replace",
+  );
+
+  const first = makeCtx({
+    parsedBody: {
+      model: "e2e-mock-model",
+      messages: [
+        {
+          role: "tool",
+          content: subagentAwaitingUserEnvelope({ taskId: "sub-first" }),
+        },
+        { role: "user", content: "my answer" },
+      ],
+    },
+  });
+  assert.equal(handleLlmCompletions(first), true);
+  const firstBody = JSON.parse(first.res.body);
+  assert.equal(firstBody.choices[0].message.content, "raw sub-first");
+
+  const second = makeCtx({
+    parsedBody: {
+      model: "e2e-mock-model",
+      messages: [{ role: "user", content: "another answer" }],
+    },
+  });
+  assert.equal(handleLlmCompletions(second), true);
+  const secondBody = JSON.parse(second.res.body);
+  // No envelope → helper leaves `{{DYNAMIC_TASK_ID}}` verbatim (identity
+  // fast-path). Prior substitution must not have poisoned the stored rule.
+  assert.equal(secondBody.choices[0].message.content, "raw {{DYNAMIC_TASK_ID}}");
+});
diff --git a/scripts/mock-api/routes/llm.mjs b/scripts/mock-api/routes/llm.mjs
index 2c69bccd04..649b002709 100644
--- a/scripts/mock-api/routes/llm.mjs
+++ b/scripts/mock-api/routes/llm.mjs
@@ -7,7 +7,12 @@ import {
   setMockBehavior,
 } from "../state.mjs";
 import { buildDynamicCompletion } from "./llm/dynamic.mjs";
-import { headerValue, pickProbeText, resolveThreadKey } from "./llm/shared.mjs";
+import {
+  applyDynamicPlaceholdersToResponse,
+  headerValue,
+  pickProbeText,
+  resolveThreadKey,
+} from "./llm/shared.mjs";
 
 // The scripted `llmForcedResponses` FIFO models the *interactive* agent turn,
 // which always advertises tools (the orchestrator's delegate_* tools). Ancillary
@@ -293,9 +298,10 @@ function handleStreamingCompletion({
       if (Array.isArray(forced) && forced.length > 0) {
         const next = forced.shift();
         setMockBehavior("llmForcedResponses", JSON.stringify(forced));
+        const rendered = applyDynamicPlaceholdersToResponse(next, parsedBody);
         script = defaultStreamScript({
-          content: next.content,
-          toolCalls: next.toolCalls,
+          content: rendered.content,
+          toolCalls: rendered.toolCalls,
         });
       }
     }
@@ -309,9 +315,10 @@ function handleStreamingCompletion({
       for (const rule of rules) {
         if (!rule || typeof rule.keyword !== "string") continue;
         if (probe.includes(rule.keyword.toLowerCase())) {
+          const rendered = applyDynamicPlaceholdersToResponse(rule, parsedBody);
           script = defaultStreamScript({
-            content: rule.content,
-            toolCalls: rule.toolCalls,
+            content: rendered.content,
+            toolCalls: rendered.toolCalls,
           });
           break;
         }
@@ -327,16 +334,20 @@ function handleStreamingCompletion({
     ) {
       script = dynamic.streamScript;
     } else {
+      const renderedRule = applyDynamicPlaceholdersToResponse(rule, parsedBody);
       const fallback =
-        typeof rule?.content === "string" && rule.content.length > 0
-          ? rule.content
+        typeof renderedRule?.content === "string" &&
+        renderedRule.content.length > 0
+          ? renderedRule.content
           : typeof mockBehavior.llmFallbackContent === "string" &&
               mockBehavior.llmFallbackContent.length > 0
             ? mockBehavior.llmFallbackContent
             : "Hello from e2e mock agent";
       script = defaultStreamScript({
         content: fallback,
-        toolCalls: Array.isArray(rule?.toolCalls) ? rule.toolCalls : undefined,
+        toolCalls: Array.isArray(renderedRule?.toolCalls)
+          ? renderedRule.toolCalls
+          : undefined,
       });
     }
   }
@@ -640,11 +651,12 @@ export function handleLlmCompletions(ctx) {
     Array.isArray(requestRule?.toolCalls) ||
     typeof requestRule?.content === "string"
   ) {
+    const rendered = applyDynamicPlaceholdersToResponse(requestRule, parsedBody);
     if (threadKey) {
       recordMockLlmTurn(threadKey, {
         requestText,
-        responseText: requestRule?.content ?? "",
-        toolCalls: requestRule?.toolCalls ?? [],
+        responseText: rendered?.content ?? "",
+        toolCalls: rendered?.toolCalls ?? [],
         model,
         family: dynamic.family,
       });
@@ -654,8 +666,8 @@ export function handleLlmCompletions(ctx) {
       Number.isInteger(requestRule?.status) ? requestRule.status : 200,
       buildResponse({
         model,
-        content: requestRule?.content ?? "",
-        toolCalls: requestRule?.toolCalls ?? [],
+        content: rendered?.content ?? "",
+        toolCalls: rendered?.toolCalls ?? [],
       }),
     );
     return true;
@@ -670,16 +682,17 @@ export function handleLlmCompletions(ctx) {
     const next = forced.shift();
     // Persist the shrunk queue back so subsequent requests advance.
     setMockBehavior("llmForcedResponses", JSON.stringify(forced));
+    const rendered = applyDynamicPlaceholdersToResponse(next, parsedBody);
     if (threadKey) {
       recordMockLlmTurn(threadKey, {
         requestText,
-        responseText: next.content ?? "",
-        toolCalls: next.toolCalls ?? [],
+        responseText: rendered.content ?? "",
+        toolCalls: rendered.toolCalls ?? [],
         model,
         family: dynamic.family,
       });
     }
-    json(res, 200, buildResponse({ model, ...next }));
+    json(res, 200, buildResponse({ model, ...rendered }));
     return true;
   }
 
@@ -690,11 +703,12 @@ export function handleLlmCompletions(ctx) {
     for (const rule of rules) {
       if (!rule || typeof rule.keyword !== "string") continue;
       if (probe.includes(rule.keyword.toLowerCase())) {
+        const rendered = applyDynamicPlaceholdersToResponse(rule, parsedBody);
         if (threadKey) {
           recordMockLlmTurn(threadKey, {
             requestText,
-            responseText: rule.content ?? "",
-            toolCalls: rule.toolCalls ?? [],
+            responseText: rendered.content ?? "",
+            toolCalls: rendered.toolCalls ?? [],
             model,
             family: dynamic.family,
           });
@@ -704,8 +718,8 @@ export function handleLlmCompletions(ctx) {
           200,
           buildResponse({
             model,
-            content: rule.content ?? "",
-            toolCalls: rule.toolCalls ?? [],
+            content: rendered.content ?? "",
+            toolCalls: rendered.toolCalls ?? [],
           }),
         );
         return true;
diff --git a/scripts/mock-api/routes/llm/shared.mjs b/scripts/mock-api/routes/llm/shared.mjs
index 092e7aa52f..ce03e22619 100644
--- a/scripts/mock-api/routes/llm/shared.mjs
+++ b/scripts/mock-api/routes/llm/shared.mjs
@@ -97,6 +97,89 @@ export function latestRoleMessage(parsedBody, role) {
   return matches[matches.length - 1] || null;
 }
 
+// Substitute `{{DYNAMIC_*}}` placeholders using values pulled from the latest
+// `[SUBAGENT_AWAITING_USER]` envelope in the message history. When the
+// orchestrator receives a paused sub-agent's envelope from
+// `awaiting_user_envelope()` (src/openhuman/agent_orchestration/tools/
+// awaiting_user.rs) it carries a runtime-generated
+// `task_id: sub-<uuid>` / `agent_id: <name>` / `worker_thread_id: ...`. A test
+// scripting the orchestrator's follow-up `continue_subagent` tool_call can't
+// know those values ahead of time — this helper substitutes them from the
+// envelope so keyword-rule fixtures can drive resume flows deterministically
+// (tinyhumansai/openhuman#4517).
+//
+// Returns `text` unchanged when it has no placeholders, no envelope is in
+// history, or `parsedBody` is missing.
+export function renderDynamicPlaceholders(text, parsedBody) {
+  if (typeof text !== "string" || text.length === 0) return text;
+  if (!text.includes("{{DYNAMIC_")) return text;
+  if (!parsedBody || !Array.isArray(parsedBody.messages)) return text;
+
+  const fields = extractLatestAwaitingUserEnvelope(parsedBody);
+  if (!fields) return text;
+
+  return text
+    .replace(/\{\{DYNAMIC_TASK_ID\}\}/g, fields.task_id ?? "{{DYNAMIC_TASK_ID}}")
+    .replace(
+      /\{\{DYNAMIC_AGENT_ID\}\}/g,
+      fields.agent_id ?? "{{DYNAMIC_AGENT_ID}}",
+    )
+    .replace(
+      /\{\{DYNAMIC_WORKER_THREAD_ID\}\}/g,
+      fields.worker_thread_id ?? "{{DYNAMIC_WORKER_THREAD_ID}}",
+    );
+}
+
+// Walk messages newest-first, find the last `[SUBAGENT_AWAITING_USER]…
+// [/SUBAGENT_AWAITING_USER]` block, and parse its `key: value` lines. Returns
+// null if not found.
+function extractLatestAwaitingUserEnvelope(parsedBody) {
+  for (let i = parsedBody.messages.length - 1; i >= 0; i -= 1) {
+    const m = parsedBody.messages[i];
+    if (!m || typeof m !== "object") continue;
+    const content = normalizeMessageContent(m.content);
+    const openIdx = content.indexOf("[SUBAGENT_AWAITING_USER]");
+    if (openIdx < 0) continue;
+    const closeIdx = content.indexOf("[/SUBAGENT_AWAITING_USER]", openIdx);
+    const body =
+      closeIdx > openIdx
+        ? content.slice(openIdx, closeIdx)
+        : content.slice(openIdx);
+    const fields = {};
+    for (const line of body.split(/\r?\n/)) {
+      const match = /^\s*([a-zA-Z_]+):\s*(.*)$/.exec(line);
+      if (!match) continue;
+      const [, key, val] = match;
+      if (!(key in fields)) fields[key] = val.trim();
+    }
+    return fields;
+  }
+  return null;
+}
+
+// Apply `renderDynamicPlaceholders` to a rule / forced-response's `content` and
+// each `toolCalls[*].arguments` (when they're stringified JSON, which the mock
+// forwards verbatim to the agent harness). No-op for entries that don't carry
+// placeholders. Returns a shallow copy — never mutates the input.
+export function applyDynamicPlaceholdersToResponse(response, parsedBody) {
+  if (!response || typeof response !== "object") return response;
+  const rendered = { ...response };
+  if (typeof rendered.content === "string") {
+    rendered.content = renderDynamicPlaceholders(rendered.content, parsedBody);
+  }
+  if (Array.isArray(rendered.toolCalls)) {
+    rendered.toolCalls = rendered.toolCalls.map((tc) => {
+      if (!tc || typeof tc !== "object") return tc;
+      const next = { ...tc };
+      if (typeof next.arguments === "string") {
+        next.arguments = renderDynamicPlaceholders(next.arguments, parsedBody);
+      }
+      return next;
+    });
+  }
+  return rendered;
+}
+
 export function resolveThreadKey(ctx) {
   const { parsedBody, req } = ctx;
   const headers = req?.headers || {};