diff --git a/packages/server/src/server/agent/providers/acp-agent.test.ts b/packages/server/src/server/agent/providers/acp-agent.test.ts
index 1e13ef190..1ab2f7fcf 100644
--- a/packages/server/src/server/agent/providers/acp-agent.test.ts
+++ b/packages/server/src/server/agent/providers/acp-agent.test.ts
@@ -65,6 +65,11 @@ interface ACPModelSelectionInternals {
 interface ACPConfiguredOverrideInternals {
   sessionId: string | null;
   connection: {
+    prompt: (input: {
+      sessionId: string;
+      messageId: string;
+      prompt: Array<{ type: "text"; text: string }>;
+    }) => Promise<PromptResponse>;
     setSessionMode: (input: { sessionId: string; modeId: string }) => Promise<void>;
     setSessionConfigOption: (input: {
       sessionId: string;
@@ -253,9 +258,11 @@ function prepareConfiguredOverrideSession(
   const setSessionConfigOption = vi.fn(async () => ({
     configOptions: options.configOptions ?? [],
   }));
+  const prompt = vi.fn(async () => ({ stopReason: "end_turn" }) as PromptResponse);
   const internals = asInternals<ACPConfiguredOverrideInternals>(session);
   internals.sessionId = "session-1";
   internals.connection = {
+    prompt,
     setSessionMode,
     setSessionConfigOption,
     unstable_setSessionModel: unstableSetSessionModel,
@@ -1001,6 +1008,100 @@ describe("ACPAgentSession Zed parity", () => {
     expect(events.some((event) => event.type === "permission_requested")).toBe(false);
   });
 
+  test("falls back to Copilot's allow-all slash command when allow_all config is not ready", async () => {
+    const setSessionConfigOption = vi.fn(async () => {
+      throw {
+        code: -32603,
+        message:
+          "Failed to set config option 'allow_all' to 'on': Error: Permission service is unavailable for this session.",
+      };
+    });
+    const prompt = vi.fn(async () => ({ stopReason: "end_turn" }) as PromptResponse);
+    const setSessionMode = vi.fn(async () => undefined);
+    const session = createCopilotSessionWithConfig(COPILOT_ALLOW_ALL_MODE_ID);
+    const { internals } = prepareConfiguredOverrideSession(session, {
+      currentMode: "https://agentclientprotocol.com/protocol/session-modes#agent",
+      availableModes: COPILOT_MODES,
+      configOptions: [
+        copilotModeConfigOption("https://agentclientprotocol.com/protocol/session-modes#agent"),
+        copilotAllowAllConfigOption("off"),
+      ],
+      connection: { prompt, setSessionConfigOption, setSessionMode },
+    });
+
+    await internals.applyConfiguredOverrides();
+
+    expect(setSessionConfigOption).toHaveBeenCalledWith({
+      sessionId: "session-1",
+      configId: "allow_all",
+      value: "on",
+    });
+    expect(prompt).toHaveBeenCalledWith({
+      sessionId: "session-1",
+      messageId: expect.any(String),
+      prompt: [{ type: "text", text: "/allow-all" }],
+    });
+    expect(setSessionMode).not.toHaveBeenCalled();
+    await expect(session.getCurrentMode()).resolves.toBe(COPILOT_ALLOW_ALL_MODE_ID);
+  });
+
+  test("refuses Copilot /allow-all fallback while a foreground turn is active", async () => {
+    const permissionError = {
+      code: -32603,
+      message:
+        "Failed to set config option 'allow_all' to 'on': Error: Permission service is unavailable for this session.",
+    };
+    const setSessionConfigOption = vi.fn(async () => {
+      throw permissionError;
+    });
+    const prompt = vi.fn(async () => ({ stopReason: "end_turn" }) as PromptResponse);
+    const setSessionMode = vi.fn(async () => undefined);
+    const session = createCopilotSessionWithConfig(COPILOT_ALLOW_ALL_MODE_ID);
+    const { internals } = prepareConfiguredOverrideSession(session, {
+      currentMode: "https://agentclientprotocol.com/protocol/session-modes#agent",
+      availableModes: COPILOT_MODES,
+      configOptions: [
+        copilotModeConfigOption("https://agentclientprotocol.com/protocol/session-modes#agent"),
+        copilotAllowAllConfigOption("off"),
+      ],
+      connection: { prompt, setSessionConfigOption, setSessionMode },
+    });
+    (internals as unknown as { activeForegroundTurnId: string | null }).activeForegroundTurnId =
+      "turn-in-flight";
+
+    await expect(internals.applyConfiguredOverrides()).rejects.toBe(permissionError);
+    expect(prompt).not.toHaveBeenCalled();
+    expect(setSessionMode).not.toHaveBeenCalled();
+  });
+
+  test("surfaces the original error if Copilot /allow-all fallback ends with a non-end_turn stop reason", async () => {
+    const permissionError = {
+      code: -32603,
+      message:
+        "Failed to set config option 'allow_all' to 'on': Error: Permission service is unavailable for this session.",
+    };
+    const setSessionConfigOption = vi.fn(async () => {
+      throw permissionError;
+    });
+    const prompt = vi.fn(async () => ({ stopReason: "refusal" }) as PromptResponse);
+    const setSessionMode = vi.fn(async () => undefined);
+    const session = createCopilotSessionWithConfig(COPILOT_ALLOW_ALL_MODE_ID);
+    const { internals } = prepareConfiguredOverrideSession(session, {
+      currentMode: "https://agentclientprotocol.com/protocol/session-modes#agent",
+      availableModes: COPILOT_MODES,
+      configOptions: [
+        copilotModeConfigOption("https://agentclientprotocol.com/protocol/session-modes#agent"),
+        copilotAllowAllConfigOption("off"),
+      ],
+      connection: { prompt, setSessionConfigOption, setSessionMode },
+    });
+
+    await expect(internals.applyConfiguredOverrides()).rejects.toBe(permissionError);
+    expect(prompt).toHaveBeenCalledTimes(1);
+    expect(setSessionMode).not.toHaveBeenCalled();
+    await expect(session.getCurrentMode()).resolves.not.toBe(COPILOT_ALLOW_ALL_MODE_ID);
+  });
+
   test("accepts Copilot's legacy autopilot mode ID as Allow All", async () => {
     const setSessionConfigOption = vi.fn(async () => ({
       configOptions: [
diff --git a/packages/server/src/server/agent/providers/acp-agent.ts b/packages/server/src/server/agent/providers/acp-agent.ts
index 5b5f3657c..9ed5ceeb0 100644
--- a/packages/server/src/server/agent/providers/acp-agent.ts
+++ b/packages/server/src/server/agent/providers/acp-agent.ts
@@ -410,6 +410,8 @@ export interface ACPProviderModeWriterContext {
   selection: ACPModeSelection;
   configOptions: SessionConfigOption[];
   logger: Logger;
+  hasActiveTurn: boolean;
+  suppressUserEcho: (params: { messageId: string; text: string }) => void;
 }
 
 export interface ACPProviderModeWriteResult {
@@ -1337,6 +1339,11 @@ export class ACPAgentSession implements AgentSession, ACPClient {
       selection,
       configOptions: this.configOptions,
       logger: this.logger,
+      hasActiveTurn: this.activeForegroundTurnId !== null,
+      suppressUserEcho: ({ messageId, text }) => {
+        this.suppressUserEchoMessageId = messageId;
+        this.suppressUserEchoText = text;
+      },
     };
   }
 
diff --git a/packages/server/src/server/agent/providers/copilot-acp-agent.ts b/packages/server/src/server/agent/providers/copilot-acp-agent.ts
index d6a8fadf9..607297081 100644
--- a/packages/server/src/server/agent/providers/copilot-acp-agent.ts
+++ b/packages/server/src/server/agent/providers/copilot-acp-agent.ts
@@ -1,4 +1,5 @@
 import type { Logger } from "pino";
+import { randomUUID } from "node:crypto";
 import { homedir } from "node:os";
 import type { SessionConfigOption } from "@agentclientprotocol/sdk";
 
@@ -43,6 +44,8 @@ export const COPILOT_ALLOW_ALL_MODE_ID = "allow-all";
 const COPILOT_ALLOW_ALL_CONFIG_ID = "allow_all";
 const COPILOT_ALLOW_ALL_ON = "on";
 const COPILOT_ALLOW_ALL_OFF = "off";
+const COPILOT_ALLOW_ALL_COMMAND = "/allow-all";
+const COPILOT_PERMISSION_SERVICE_UNAVAILABLE = "Permission service is unavailable for this session";
 type SelectConfigOption = Extract<SessionConfigOption, { type: "select" }>;
 
 export const COPILOT_MODES: AgentMode[] = [
@@ -224,15 +227,53 @@ export async function writeCopilotProviderMode(
   if (!requestsAllowAll) {
     return { handled: false };
   }
-  const response = await context.connection.setSessionConfigOption({
-    sessionId: context.sessionId,
-    configId: COPILOT_ALLOW_ALL_CONFIG_ID,
-    value: COPILOT_ALLOW_ALL_ON,
-  });
+  let configOptions: SessionConfigOption[] | undefined;
+  try {
+    const response = await context.connection.setSessionConfigOption({
+      sessionId: context.sessionId,
+      configId: COPILOT_ALLOW_ALL_CONFIG_ID,
+      value: COPILOT_ALLOW_ALL_ON,
+    });
+    configOptions = response.configOptions;
+  } catch (error) {
+    if (!isCopilotPermissionServiceUnavailableError(error)) {
+      throw error;
+    }
+    if (context.hasActiveTurn) {
+      // Issuing a second concurrent prompt on the same ACP session is unsafe; let the caller retry once the turn settles.
+      context.logger.warn(
+        { err: error },
+        "Copilot allow_all config write failed and a foreground turn is active; refusing /allow-all fallback",
+      );
+      throw error;
+    }
+    context.logger.warn(
+      { err: error },
+      "Copilot allow_all config write failed before permission service was ready; falling back to /allow-all",
+    );
+    const fallbackMessageId = randomUUID();
+    context.suppressUserEcho({
+      messageId: fallbackMessageId,
+      text: COPILOT_ALLOW_ALL_COMMAND,
+    });
+    const promptResponse = await context.connection.prompt({
+      sessionId: context.sessionId,
+      messageId: fallbackMessageId,
+      prompt: [{ type: "text", text: COPILOT_ALLOW_ALL_COMMAND }],
+    });
+    if (promptResponse.stopReason !== "end_turn") {
+      context.logger.warn(
+        { stopReason: promptResponse.stopReason },
+        "Copilot /allow-all fallback returned an unexpected stop reason; surfacing the original error",
+      );
+      throw error;
+    }
+    configOptions = setCopilotAllowAllConfigValue(context.configOptions, COPILOT_ALLOW_ALL_ON);
+  }
   return {
     handled: true,
     currentModeId: COPILOT_ALLOW_ALL_MODE_ID,
-    configOptions: response.configOptions,
+    configOptions,
   };
 }
 
@@ -261,3 +302,34 @@ function isCopilotAllowAllEnabled(configOptions: SessionConfigOption[]): boolean
       option.currentValue === COPILOT_ALLOW_ALL_ON,
   );
 }
+
+function setCopilotAllowAllConfigValue(
+  configOptions: SessionConfigOption[],
+  value: typeof COPILOT_ALLOW_ALL_ON | typeof COPILOT_ALLOW_ALL_OFF,
+): SessionConfigOption[] {
+  return configOptions.map((option) => {
+    if (option.type !== "select" || option.id !== COPILOT_ALLOW_ALL_CONFIG_ID) {
+      return option;
+    }
+    return { ...option, currentValue: value };
+  });
+}
+
+function isCopilotPermissionServiceUnavailableError(error: unknown): boolean {
+  const message = getErrorMessage(error);
+  return message?.includes(COPILOT_PERMISSION_SERVICE_UNAVAILABLE) ?? false;
+}
+
+function getErrorMessage(error: unknown): string | null {
+  if (error instanceof Error) {
+    return error.message;
+  }
+  if (!isRecord(error)) {
+    return null;
+  }
+  return typeof error.message === "string" ? error.message : null;
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return value != null && typeof value === "object" && !Array.isArray(value);
+}