diff --git a/packages/provider-opencode/src/server/adapter.test.ts b/packages/provider-opencode/src/server/adapter.test.ts
index 759545fff0d19..55faec513c7d9 100644
--- a/packages/provider-opencode/src/server/adapter.test.ts
+++ b/packages/provider-opencode/src/server/adapter.test.ts
@@ -15,6 +15,7 @@ import {
   ThreadId,
   type OrchestrationV2ProviderThread,
   type OrchestrationV2ProviderTurn,
+  type ModelSelection,
 } from "@t3tools/contracts";
 import { OpenCodeSettings } from "../settings.ts";
 import * as Effect from "effect/Effect";
@@ -145,15 +146,22 @@ const makeOpenCodeRuntimeHarness = Effect.fn("makeOpenCodeRuntimeHarness")(funct
   nativeSessionId: string,
   client: object,
   host: Partial<ProviderHost.ProviderHost["Service"]> = {},
+  selection: {
+    readonly options?: ModelSelection["options"];
+    readonly interactionMode?: ProviderAdapter.ProviderAdapterV2RuntimePolicy["interactionMode"];
+  } = {},
 ) {
   const instanceId = ProviderInstanceId.make(`opencode-${suffix}`);
   const threadId = ThreadId.make(`thread-opencode-${suffix}`);
   const modelSelection = {
     instanceId,
     model: "anthropic/claude-sonnet",
-    options: [],
+    options: selection.options ?? [],
   };
-  const policy = runtimePolicy("full-access", { cwd: "/workspace" });
+  const policy = runtimePolicy("full-access", {
+    cwd: "/workspace",
+    interactionMode: selection.interactionMode ?? "default",
+  });
   const adapter = yield* makeOpenCodeAdapterV2({
     instanceId,
     settings: OPEN_CODE_TEST_SETTINGS,
@@ -194,7 +202,7 @@ const makeOpenCodeRuntimeHarness = Effect.fn("makeOpenCodeRuntimeHarness")(funct
         providerInstanceId: modelSelection.instanceId,
         modelSelection,
         runtimeMode: "full-access",
-        interactionMode: "default",
+        interactionMode: policy.interactionMode,
         branch: null,
         worktreePath: null,
         activeProviderThreadId: providerThread.id,
@@ -240,6 +248,73 @@ const makeOpenCodeRuntimeHarness = Effect.fn("makeOpenCodeRuntimeHarness")(funct
 });
 
 describe("OpenCodeAdapterV2", () => {
+  it.effect.each(["custom", "plan", "default"] as const)(
+    "keeps %s agent and reasoning options when steering",
+    (scenario) =>
+      Effect.gen(function* () {
+        const nativeEvents = asyncEventStream();
+        const prompts: Array<Parameters<OpencodeClient["session"]["promptAsync"]>[0]> = [];
+        const harness = yield* makeOpenCodeRuntimeHarness(
+          `steer-options-${scenario}`,
+          "root",
+          {
+            event: { subscribe: async () => ({ stream: nativeEvents.stream }) },
+            session: {
+              create: async () => ({ data: { id: "root", time: { created: 1, updated: 1 } } }),
+              get: async () => ({ data: { id: "root", time: { created: 1, updated: 1 } } }),
+              messages: async () => ({ data: [] }),
+              promptAsync: async (input: (typeof prompts)[number]) => {
+                prompts.push(input);
+                return { data: true };
+              },
+              abort: async () => ({ data: true }),
+              children: async () => ({ data: [] }),
+            },
+          },
+          {},
+          {
+            interactionMode: scenario === "default" ? "default" : "plan",
+            options:
+              scenario === "custom"
+                ? [
+                    { id: "agent", value: "agent-b" },
+                    { id: "variant", value: "high" },
+                  ]
+                : [],
+          },
+        );
+        yield* harness.startTurn();
+        const snapshot = yield* harness.runtime.readThreadSnapshot({
+          providerThread: harness.providerThread,
+        });
+        yield* harness.runtime.steerTurn({
+          threadId: harness.threadId,
+          runId: harness.runId,
+          providerThread: harness.providerThread,
+          providerTurnId: snapshot.providerTurns.at(-1)!.id,
+          message: {
+            messageId: MessageId.make("message-steer-options"),
+            text: "Continue with the same agent",
+            attachments: [],
+            createdBy: "user",
+            creationSource: "web",
+          },
+        });
+        assert.lengthOf(prompts, 2);
+        assert.equal(
+          prompts[1]?.agent,
+          scenario === "custom" ? "agent-b" : scenario === "plan" ? "plan" : undefined,
+        );
+        assert.equal(prompts[1]?.variant, scenario === "custom" ? "high" : undefined);
+        assert.isNotEmpty(prompts[0]?.system);
+        assert.equal(prompts[1]?.system, prompts[0]?.system);
+        assert.notEqual(prompts[1]?.messageID, prompts[0]?.messageID);
+      }).pipe(
+        Effect.provide(Layer.merge(IdAllocator.layer, McpProviderSessions.layer)),
+        Effect.scoped,
+      ),
+  );
+
   it.effect("applies a changed runtime policy to the session on resume and turn start", () =>
     Effect.gen(function* () {
       const updates: Array<{ sessionID: string; permission: unknown }> = [];
diff --git a/packages/provider-opencode/src/server/adapter.ts b/packages/provider-opencode/src/server/adapter.ts
index bad3e8cd7b89a..a4fe90c2ef06d 100644
--- a/packages/provider-opencode/src/server/adapter.ts
+++ b/packages/provider-opencode/src/server/adapter.ts
@@ -2927,6 +2927,23 @@ export const makeOpenCodeAdapterV2 = Effect.fn("makeOpenCodeAdapterV2")(function
           };
         });
 
+        const promptOptions = (turn: ActiveOpenCodeTurn) => {
+          const agent =
+            getModelSelectionStringOptionValue(turn.modelSelection, "agent") ??
+            (turn.runtimePolicy.interactionMode === "plan" ? "plan" : undefined);
+          const variant = getModelSelectionStringOptionValue(turn.modelSelection, "variant");
+          return {
+            ...(agent === undefined ? {} : { agent }),
+            ...(variant === undefined ? {} : { variant }),
+            system: [
+              orchestrationSystemPrompt,
+              buildRuntimeInstructions({ harness: "OpenCode", model: turn.modelSelection.model }),
+            ]
+              .filter(Boolean)
+              .join("\n\n"),
+          };
+        };
+
         // Native commands await generation; user-message receipts admit their background requests.
         const submitPrompt = Effect.fn("OpenCode.submitPrompt")(function* (
           state: OpenCodeThreadState,
@@ -3249,22 +3266,6 @@ export const makeOpenCodeAdapterV2 = Effect.fn("makeOpenCodeAdapterV2")(function
                 );
                 return;
               }
-              const systemPrompt = [
-                orchestrationSystemPrompt,
-                buildRuntimeInstructions({
-                  harness: "OpenCode",
-                  model: turnInput.modelSelection.model,
-                }),
-              ]
-                .filter(Boolean)
-                .join("\n\n");
-              const agent =
-                getModelSelectionStringOptionValue(turnInput.modelSelection, "agent") ??
-                (turnInput.runtimePolicy.interactionMode === "plan" ? "plan" : undefined);
-              const variant = getModelSelectionStringOptionValue(
-                turnInput.modelSelection,
-                "variant",
-              );
               yield* submitPrompt(
                 state,
                 turn,
@@ -3272,9 +3273,7 @@ export const makeOpenCodeAdapterV2 = Effect.fn("makeOpenCodeAdapterV2")(function
                   sessionID: sessionId,
                   messageID: turn.admissionMessageId!,
                   model: parsedModel,
-                  ...(agent === undefined ? {} : { agent }),
-                  ...(variant === undefined ? {} : { variant }),
-                  system: systemPrompt,
+                  ...promptOptions(turn),
                   parts,
                 },
                 admissionAbortController!,
@@ -3385,6 +3384,7 @@ export const makeOpenCodeAdapterV2 = Effect.fn("makeOpenCodeAdapterV2")(function
                   sessionID: sessionId,
                   messageID: turn.admissionMessageId,
                   model: parsedModel,
+                  ...promptOptions(turn),
                   parts,
                 },
                 admissionAbortController!,