diff --git a/apps/server/src/provider/Layers/OpenCodeAdapter.test.ts b/apps/server/src/provider/Layers/OpenCodeAdapter.test.ts
index eea328e05d1e..2b5c0717a193 100644
--- a/apps/server/src/provider/Layers/OpenCodeAdapter.test.ts
+++ b/apps/server/src/provider/Layers/OpenCodeAdapter.test.ts
@@ -61,6 +61,8 @@ const runtimeMock = {
     sessionCreateInputs: [] as Array<Record<string, unknown>>,
     authHeaders: [] as Array<string | null>,
     abortCalls: [] as string[],
+    onAbort: null as ((sessionID: string) => void) | null,
+    sessionChildrenById: new Map<string, Array<{ id: string }>>(),
     closeCalls: [] as string[],
     revertCalls: [] as Array<{ sessionID: string; messageID?: string }>,
     promptCalls: [] as Array<unknown>,
@@ -81,6 +83,8 @@ const runtimeMock = {
     this.state.sessionCreateInputs.length = 0;
     this.state.authHeaders.length = 0;
     this.state.abortCalls.length = 0;
+    this.state.onAbort = null;
+    this.state.sessionChildrenById.clear();
     this.state.closeCalls.length = 0;
     this.state.revertCalls.length = 0;
     this.state.promptCalls.length = 0;
@@ -176,7 +180,11 @@ const OpenCodeRuntimeTestDouble: OpenCodeRuntimeShape = {
         },
         abort: async ({ sessionID }: { sessionID: string }) => {
           runtimeMock.state.abortCalls.push(sessionID);
+          runtimeMock.state.onAbort?.(sessionID);
         },
+        children: async ({ sessionID }: { sessionID: string }) => ({
+          data: runtimeMock.state.sessionChildrenById.get(sessionID) ?? [],
+        }),
         promptAsync: async (input: unknown) => {
           runtimeMock.state.promptCalls.push(input);
           if (runtimeMock.state.promptAsyncError) {
@@ -602,6 +610,40 @@ it.layer(OpenCodeAdapterTestLayer)("OpenCodeAdapterLive", (it) => {
     }),
   );
 
+  it.effect("interrupts the parent before all surviving OpenCode child sessions", () =>
+    Effect.gen(function* () {
+      const adapter = yield* OpenCodeAdapter;
+      const threadId = asThreadId("thread-opencode-children");
+      yield* adapter.startSession({
+        provider: ProviderDriverKind.make("opencode"),
+        threadId,
+        runtimeMode: "full-access",
+      });
+
+      runtimeMock.state.sessionChildrenById.set("http://127.0.0.1:9999/session", [
+        { id: "child-a" },
+        { id: "child-b" },
+      ]);
+      runtimeMock.state.onAbort = (sessionID) => {
+        if (sessionID === "http://127.0.0.1:9999/session") {
+          runtimeMock.state.sessionChildrenById
+            .get("http://127.0.0.1:9999/session")
+            ?.push({ id: "child-created-during-parent-abort" });
+        }
+      };
+
+      yield* adapter.interruptTurn(threadId);
+
+      NodeAssert.equal(runtimeMock.state.abortCalls[0], "http://127.0.0.1:9999/session");
+      NodeAssert.deepEqual(
+        runtimeMock.state.abortCalls.slice(1).sort(),
+        ["child-a", "child-b", "child-created-during-parent-abort"].sort(),
+      );
+
+      yield* adapter.stopSession(threadId);
+    }),
+  );
+
   it.effect("emits one session.exited event when stopping a session", () =>
     Effect.gen(function* () {
       const adapter = yield* OpenCodeAdapter;
diff --git a/apps/server/src/provider/Layers/OpenCodeAdapter.ts b/apps/server/src/provider/Layers/OpenCodeAdapter.ts
index 8f7e42c11d7c..9d44256e2ad2 100644
--- a/apps/server/src/provider/Layers/OpenCodeAdapter.ts
+++ b/apps/server/src/provider/Layers/OpenCodeAdapter.ts
@@ -1555,12 +1555,37 @@ export function makeOpenCodeAdapter(
       };
     });
 
+    const abortOpenCodeSessionTree = Effect.fn("abortOpenCodeSessionTree")(function* (
+      context: OpenCodeSessionContext,
+    ) {
+      // Abort the parent first so it cannot spawn another child after we take the
+      // children snapshot. Older OpenCode releases do not reliably propagate this
+      // cancellation, so enumerate and abort any surviving children afterwards.
+      yield* runOpenCodeSdk("session.abort", () =>
+        context.client.session.abort({ sessionID: context.openCodeSessionId }),
+      ).pipe(Effect.mapError(toRequestError));
+
+      const children = yield* runOpenCodeSdk("session.children", () =>
+        context.client.session.children({ sessionID: context.openCodeSessionId }),
+      ).pipe(
+        Effect.map((response) => response.data ?? []),
+        Effect.orElseSucceed(() => []),
+      );
+
+      yield* Effect.forEach(
+        children,
+        (child) =>
+          runOpenCodeSdk("session.abort", () =>
+            context.client.session.abort({ sessionID: child.id }),
+          ).pipe(Effect.ignore),
+        { concurrency: "unbounded", discard: true },
+      );
+    });
+
     const interruptTurn: OpenCodeAdapterShape["interruptTurn"] = Effect.fn("interruptTurn")(
       function* (threadId, turnId) {
         const context = yield* ensureSessionContext(sessions, threadId);
-        yield* runOpenCodeSdk("session.abort", () =>
-          context.client.session.abort({ sessionID: context.openCodeSessionId }),
-        ).pipe(Effect.mapError(toRequestError));
+        yield* abortOpenCodeSessionTree(context);
         if (turnId ?? context.activeTurnId) {
           yield* emit({
             ...(yield* buildEventBase({