refactor(server): share the question card's multi-select answer splitting

OpenCode v2 and OMP both read the question card's comma-joined
multi-select answer back into option labels. Keep that in one helper
next to the providers so the two cannot drift.

Co-authored-by: Grant Ammons <grant@grant.dev>

packages/server/src/server/agent/providers/omp/question-ui.ts

@@ -3,6 +3,7 @@ import type {
   AgentPermissionResponse,
   AgentProvider,
 } from "../../agent-sdk-types.js";
+import { splitMultiSelectAnswer } from "../question-card-answer.js";
 import type { OmpAgentMessage, OmpRuntimeEvent } from "./rpc-types.js";
 
 type UiRequest = Extract<OmpRuntimeEvent, { type: "extension_ui_request" }>;
@@ -176,21 +177,7 @@ function selectedAnswer(
     return labels.includes(answer)
       ? { selected: [answer], custom: null }
       : { selected: [], custom: answer };
-
-  // The shared question UI sends a comma-joined answer in click order. Consume
-  // exact option labels from the front; any remaining text is the Other answer.
-  let remaining = answer;
-  const selected: string[] = [];
-  while (remaining.length > 0) {
-    const label = labels
-      .filter((candidate) => !selected.includes(candidate))
-      .sort((left, right) => right.length - left.length)
-      .find((candidate) => remaining === candidate || remaining.startsWith(`${candidate}, `));
-    if (!label) break;
-    selected.push(label);
-    remaining = remaining === label ? "" : remaining.slice(label.length + 2);
-  }
-  return { selected, custom: remaining || null };
+  return splitMultiSelectAnswer(answer, labels);
 }
 
 /** Owns OMP question mapping and the ask tool's multi-RPC answer sequence. */

packages/server/src/server/agent/providers/opencode/v2/permissions.test.ts

@@ -109,7 +109,7 @@ describe("OpenCode v2 question tool", () => {
               { value: "Explore", label: "Explore", description: "Map the codebase" },
               { value: "Fix a bug", label: "Fix a bug", description: "Track down a bug" },
             ],
-            multiple: false,
+            multiSelect: false,
             allowOther: true,
           },
         ],
@@ -129,6 +129,99 @@ describe("OpenCode v2 question tool", () => {
       await session.close();
     }
   });
+
+  test("answers a multi-select question with the checked options and a typed answer", async () => {
+    const harness = new V2Harness();
+    harness.api.session.form.list = async () => [
+      {
+        id: "question",
+        sessionID: "session",
+        title: "Questions",
+        fields: [
+          {
+            key: "q0",
+            title: "Fixes",
+            description: "Which fixes should I make?",
+            type: "multiselect",
+            options: [
+              { value: "delete", label: "Delete both" },
+              { value: "delete-and-fix", label: "Delete both, fix code" },
+              { value: "email", label: "Email the user" },
+            ],
+            custom: true,
+          },
+        ],
+      },
+    ];
+    const answers: Parameters<V2Api["session"]["form"]["reply"]>[0][] = [];
+    harness.api.session.form.reply = async (input) => {
+      answers.push(input);
+    };
+    const client = new OpenCodeV2AgentClient({
+      logger: createTestLogger(),
+      runtime: harness.runtime,
+    });
+    const session = await client.createSession({ provider: "opencode", cwd: "/tmp/project" });
+    try {
+      const [request] = session.getPendingPermissions();
+      expect(request.input).toMatchObject({ questions: [{ header: "Fixes", multiSelect: true }] });
+      await session.respondToPermission("question", {
+        behavior: "allow",
+        updatedInput: {
+          answers: { Fixes: "Delete both, fix code, Email the user, Also check the logs" },
+        },
+      });
+      expect(answers).toEqual([
+        {
+          sessionID: "session",
+          formID: "question",
+          answer: { q0: ["delete-and-fix", "email", "Also check the logs"] },
+        },
+      ]);
+      expect(session.getPendingPermissions()).toHaveLength(0);
+    } finally {
+      await session.close();
+    }
+  });
+
+  test("rejects typed text on a multi-select question that has no typed answer", async () => {
+    const harness = new V2Harness();
+    harness.api.session.form.list = async () => [
+      {
+        id: "question",
+        sessionID: "session",
+        title: "Questions",
+        fields: [
+          {
+            key: "q0",
+            title: "Fixes",
+            type: "multiselect",
+            options: [{ value: "delete", label: "Delete both" }],
+          },
+        ],
+      },
+    ];
+    const answers: Parameters<V2Api["session"]["form"]["reply"]>[0][] = [];
+    harness.api.session.form.reply = async (input) => {
+      answers.push(input);
+    };
+    const client = new OpenCodeV2AgentClient({
+      logger: createTestLogger(),
+      runtime: harness.runtime,
+    });
+    const session = await client.createSession({ provider: "opencode", cwd: "/tmp/project" });
+    try {
+      await expect(
+        session.respondToPermission("question", {
+          behavior: "allow",
+          updatedInput: { answers: { Fixes: "Delete both, Something else" } },
+        }),
+      ).rejects.toThrow("Invalid answer for OpenCode question q0");
+      expect(answers).toEqual([]);
+    } finally {
+      await session.close();
+    }
+  });
 });
 
 describe("OpenCode v2 permission routing", () => {

packages/server/src/server/agent/providers/opencode/v2/permissions.ts

@@ -7,6 +7,7 @@ import type {
   AgentSessionConfig,
   AgentStreamEvent,
 } from "../../../agent-sdk-types.js";
+import { splitMultiSelectAnswer } from "../../question-card-answer.js";
 
 export class SessionPermissions {
   private readonly pending = new Map<string, AgentPermissionRequest>();
@@ -103,7 +104,7 @@ export class SessionPermissions {
             header: field.title ?? field.key,
             question: field.description ?? field.title ?? field.key,
             options: "options" in field ? field.options : undefined,
-            multiple: field.type === "multiselect",
+            multiSelect: field.type === "multiselect",
             allowOther: "custom" in field && field.custom === true,
           })),
         },
@@ -137,8 +138,8 @@ function formAnswer(field: FormInfo["fields"][number], value: unknown): FormValu
     );
   };
   if (field.type === "multiselect") {
-    if (Array.isArray(value) && value.every((item: unknown) => typeof item === "string"))
-      return value.map(labelValue);
+    const selected = multiSelectAnswer(field, value);
+    if (selected) return selected.map(labelValue);
   } else if (field.type === "string" && typeof value === "string") {
     return labelValue(value);
   } else if (field.type === "boolean") {
@@ -156,3 +157,17 @@ function formAnswer(field: FormInfo["fields"][number], value: unknown): FormValu
   }
   throw new Error(`Invalid answer for OpenCode question ${field.key}`);
 }
+
+type MultiSelectField = Extract<FormInfo["fields"][number], { type: "multiselect" }>;
+
+function multiSelectAnswer(field: MultiSelectField, value: unknown): string[] | undefined {
+  if (Array.isArray(value) && value.every((item: unknown) => typeof item === "string"))
+    return value;
+  if (typeof value !== "string") return undefined;
+  const { selected, custom } = splitMultiSelectAnswer(
+    value,
+    field.options.map((option) => option.label),
+  );
+  if (custom === null) return selected;
+  return field.custom === true ? [...selected, custom] : undefined;
+}

packages/server/src/server/agent/providers/question-card-answer.test.ts

@@ -0,0 +1,32 @@
+import { describe, expect, test } from "vitest";
+
+import { splitMultiSelectAnswer } from "./question-card-answer.js";
+
+describe("splitMultiSelectAnswer", () => {
+  const labels = ["Delete both", "Delete both, fix code", "Email the user"];
+
+  test("splits checked labels in click order", () => {
+    expect(splitMultiSelectAnswer("Email the user, Delete both", labels)).toEqual({
+      selected: ["Email the user", "Delete both"],
+      custom: null,
+    });
+  });
+
+  test("keeps a label that contains a comma as one selection", () => {
+    expect(splitMultiSelectAnswer("Delete both, fix code, Email the user", labels)).toEqual({
+      selected: ["Delete both, fix code", "Email the user"],
+      custom: null,
+    });
+  });
+
+  test("returns trailing text as the typed answer", () => {
+    expect(splitMultiSelectAnswer("Delete both, Also check the logs", labels)).toEqual({
+      selected: ["Delete both"],
+      custom: "Also check the logs",
+    });
+    expect(splitMultiSelectAnswer("Only typed text", labels)).toEqual({
+      selected: [],
+      custom: "Only typed text",
+    });
+  });
+});

packages/server/src/server/agent/providers/question-card-answer.ts

@@ -0,0 +1,23 @@
+/**
+ * The shared question card sends a multi-select answer as one string: the checked option
+ * labels in click order, then any typed answer, joined with ", ". Consume exact option
+ * labels from the front, longest first so a label containing ", " wins over its prefix;
+ * any remaining text is the typed answer.
+ */
+export function splitMultiSelectAnswer(
+  answer: string,
+  labels: string[],
+): { selected: string[]; custom: string | null } {
+  let remaining = answer;
+  const selected: string[] = [];
+  while (remaining.length > 0) {
+    const label = labels
+      .filter((candidate) => !selected.includes(candidate))
+      .sort((left, right) => right.length - left.length)
+      .find((candidate) => remaining === candidate || remaining.startsWith(`${candidate}, `));
+    if (!label) break;
+    selected.push(label);
+    remaining = remaining === label ? "" : remaining.slice(label.length + 2);
+  }
+  return { selected, custom: remaining || null };
+}