fix(acp): preserve typed form answers across clients

apps/mobile/src/features/threads/PendingUserInputCard.tsx

@@ -270,6 +270,23 @@ export function PendingUserInputCard(props: PendingUserInputCardProps) {
         ) : null}
         {props.pendingUserInput.questions.map((question) => {
           const draft = props.drafts[question.id];
+          const minSelections = question.minSelections ?? (question.maxSelections === 0 ? 0 : 1);
+          const maxSelections = question.maxSelections;
+          const selectionHint =
+            maxSelections === 0
+              ? "Leave all options unselected."
+              : maxSelections === minSelections
+                ? `Select ${minSelections} option${minSelections === 1 ? "" : "s"}.`
+                : maxSelections !== undefined
+                  ? minSelections === 0
+                    ? `Select up to ${maxSelections} option${maxSelections === 1 ? "" : "s"}.`
+                    : `Select ${minSelections} to ${maxSelections} options.`
+                  : minSelections === 0
+                    ? "Select any number of options."
+                    : `Select at least ${minSelections} option${minSelections === 1 ? "" : "s"}.`;
+          const showSelectionHint =
+            question.multiSelect &&
+            (question.minSelections !== undefined || maxSelections !== undefined);
           return (
             <View key={question.id} className="gap-2 pt-1">
               <Text className="font-t3-bold text-xs uppercase tracking-[1px] text-foreground-muted">
@@ -278,6 +295,14 @@ export function PendingUserInputCard(props: PendingUserInputCardProps) {
               <Text className="font-sans text-base leading-snug text-foreground">
                 {question.question}
               </Text>
+              {showSelectionHint || question.required === false ? (
+                <Text className="font-sans text-sm leading-5 text-foreground-muted">
+                  {showSelectionHint ? selectionHint : null}
+                  {question.required === false
+                    ? `${showSelectionHint ? " " : ""}You can skip this question.`
+                    : null}
+                </Text>
+              ) : null}
               <View className="gap-2">
                 {question.options.map((option) => {
                   const optionValue = option.value ?? option.label.trim();

apps/mobile/src/lib/threadActivity.test.ts

@@ -1989,6 +1989,102 @@ describe("pending user input answers", () => {
     });
   });
 
+  it("omits unanswered optional questions while preserving required defaults", () => {
+    const question = { ...singleSelectQuestion, required: false };
+
+    expect(
+      buildPendingUserInputAnswers([question, multiSelectQuestion], {
+        scope: { selectedOptionValues: ["Orders"] },
+      }),
+    ).toEqual({ scope: ["Orders"] });
+    expect(buildPendingUserInputAnswers([question], { runtime: { customAnswer: "   " } })).toEqual(
+      {},
+    );
+    expect(buildPendingUserInputAnswers([singleSelectQuestion], {})).toBeNull();
+  });
+
+  it.each([
+    { attachmentsBlocked: true },
+    { attachmentCount: 1, attachmentsBlocked: true },
+    { attachmentCount: 1 },
+    { customAnswer: "Unlisted answer" },
+    { selectedOptionValues: ["unknown"] },
+  ])("keeps invalid optional drafts blocking submission: %j", (draft) => {
+    const question = { ...singleSelectQuestion, required: false, allowCustomAnswer: false };
+
+    expect(buildPendingUserInputAnswers([question], { runtime: draft })).toBeNull();
+  });
+
+  it.each([0, undefined])(
+    "submits empty arrays with a zero maximum and minimum %j",
+    (minSelections) => {
+      const question = {
+        ...multiSelectQuestion,
+        allowCustomAnswer: false,
+        required: true,
+        ...(minSelections === undefined ? {} : { minSelections }),
+        maxSelections: 0,
+      };
+
+      expect(buildPendingUserInputAnswers([question], {})).toEqual({ scope: [] });
+      expect(
+        buildPendingUserInputAnswers([question], { scope: { selectedOptionValues: ["Orders"] } }),
+      ).toBeNull();
+      expect(buildPendingUserInputAnswers([{ ...question, required: false }], {})).toEqual({});
+    },
+  );
+
+  it("requires one selection when no zero maximum is declared", () => {
+    const question = { ...multiSelectQuestion, required: true, allowCustomAnswer: false };
+
+    expect(buildPendingUserInputAnswers([question], {})).toBeNull();
+    expect(buildPendingUserInputAnswers([{ ...question, maxSelections: 2 }], {})).toBeNull();
+  });
+
+  it("enforces multi-select limits and omits unanswered optional arrays", () => {
+    const question = {
+      ...multiSelectQuestion,
+      options: [...multiSelectQuestion.options, { label: "Sales", description: "Sales" }],
+      allowCustomAnswer: false,
+      minSelections: 2,
+      maxSelections: 2,
+    };
+
+    expect(buildPendingUserInputAnswers([question], {})).toBeNull();
+    expect(
+      buildPendingUserInputAnswers([question], { scope: { selectedOptionValues: ["Orders"] } }),
+    ).toBeNull();
+    expect(
+      buildPendingUserInputAnswers([question], {
+        scope: { selectedOptionValues: ["Orders", "Listings"] },
+      }),
+    ).toEqual({ scope: ["Orders", "Listings"] });
+    expect(
+      buildPendingUserInputAnswers([question], {
+        scope: { selectedOptionValues: ["Orders", "Listings", "Sales"] },
+      }),
+    ).toBeNull();
+    expect(buildPendingUserInputAnswers([{ ...question, required: false }], {})).toEqual({});
+    expect(
+      buildPendingUserInputAnswers([{ ...question, required: false }], {
+        scope: { selectedOptionValues: ["Orders"] },
+      }),
+    ).toBeNull();
+    expect(
+      buildPendingUserInputAnswers([{ ...question, required: false }], {
+        scope: { selectedOptionValues: ["unknown"] },
+      }),
+    ).toBeNull();
+    expect(
+      buildPendingUserInputAnswers([{ ...question, required: false, minSelections: 0 }], {
+        scope: { selectedOptionValues: ["unknown"] },
+      }),
+    ).toBeNull();
+    expect(
+      buildPendingUserInputAnswers([multiSelectQuestion], { scope: { attachmentCount: 1 } }),
+    ).toEqual({ scope: "" });
+  });
+
   it("clears selected options while a custom answer is active", () => {
     expect(
       setPendingUserInputCustomAnswer(

apps/mobile/src/lib/threadActivity.ts

@@ -367,11 +367,27 @@ function resolvePendingUserInputAnswer(
 
   const selectedOptionValues = normalizeSelectedOptionValues(question, draft?.selectedOptionValues);
   if (question.multiSelect) {
-    return selectedOptionValues.length > 0
-      ? selectedOptionValues
-      : question.allowCustomAnswer !== false && (draft?.attachmentCount ?? 0) > 0
+    if (
+      selectedOptionValues.length === 0 &&
+      ((draft?.selectedOptionValues?.length ?? 0) > 0 ||
+        normalizeDraftAnswer(draft?.customAnswer) !== null ||
+        (question.allowCustomAnswer === false && (draft?.attachmentCount ?? 0) > 0))
+    )
+      return null;
+    if (
+      selectedOptionValues.length <
+        (question.minSelections ?? (question.maxSelections === 0 ? 0 : 1)) ||
+      (question.maxSelections !== undefined && selectedOptionValues.length > question.maxSelections)
+    ) {
+      return selectedOptionValues.length === 0 &&
+        question.minSelections === undefined &&
+        question.maxSelections === undefined &&
+        question.allowCustomAnswer !== false &&
+        (draft?.attachmentCount ?? 0) > 0
         ? ""
         : null;
+    }
+    return selectedOptionValues;
   }
   return (
     selectedOptionValues[0] ??
@@ -1632,7 +1648,16 @@ export function buildPendingUserInputAnswers(
   const answers: Record<string, string | ReadonlyArray<string>> = {};
 
   for (const question of questions) {
-    const answer = resolvePendingUserInputAnswer(question, draftAnswers[question.id]);
+    const draft = draftAnswers[question.id];
+    if (
+      question.required === false &&
+      !draft?.attachmentsBlocked &&
+      normalizeDraftAnswer(draft?.customAnswer) === null &&
+      (draft?.selectedOptionValues?.length ?? 0) === 0 &&
+      (draft?.attachmentCount ?? 0) === 0
+    )
+      continue;
+    const answer = resolvePendingUserInputAnswer(question, draft);
     if (answer === null) {
       return null;
     }

apps/server/scripts/acp-mock-agent.ts

@@ -12,7 +12,7 @@ import * as NodeRuntime from "@effect/platform-node/NodeRuntime";
 
 import * as EffectAcpAgent from "effect-acp/agent";
 import * as AcpError from "effect-acp/errors";
-import type * as AcpSchema from "effect-acp/schema";
+import * as AcpSchema from "effect-acp/schema";
 import type * as AcpCompat from "effect-acp/compat";
 
 import { beginAcpMockPrompt } from "./acpMockCancellationState.ts";
@@ -34,6 +34,10 @@ const emitBackgroundToolDuringAnswer =
   process.env.T3_ACP_EMIT_BACKGROUND_TOOL_DURING_ANSWER === "1";
 const emitAskQuestion = process.env.T3_ACP_EMIT_ASK_QUESTION === "1";
 const emitElicitation = process.env.T3_ACP_EMIT_ELICITATION === "1";
+const elicitationSchemaJson = process.env.T3_ACP_ELICITATION_SCHEMA;
+const decodeElicitationSchema = Schema.decodeUnknownEffect(
+  Schema.fromJsonString(AcpSchema.ElicitationSchema),
+);
 const emitMcpToolApprovalElicitation =
   process.env.T3_ACP_EMIT_MCP_TOOL_APPROVAL_ELICITATION === "1";
 const emitUrlElicitation = process.env.T3_ACP_EMIT_URL_ELICITATION === "1";
@@ -1781,12 +1785,19 @@ const program = Effect.gen(function* () {
           sessionId: requestedSessionId,
           message: "Approve this request?",
           mode: "form",
-          requestedSchema: {
-            type: "object",
-            properties: {
-              approved: { type: "boolean", title: "Approved" },
-            },
-          },
+          requestedSchema:
+            elicitationSchemaJson === undefined
+              ? {
+                  type: "object",
+                  properties: {
+                    approved: { type: "boolean", title: "Approved" },
+                  },
+                }
+              : yield* decodeElicitationSchema(elicitationSchemaJson).pipe(
+                  Effect.mapError(() =>
+                    AcpError.AcpRequestError.invalidParams("Invalid elicitation schema"),
+                  ),
+                ),
           ...(emitMcpToolApprovalElicitation
             ? { _meta: { codex_approval_kind: "mcp_tool_call" } }
             : {}),