diff --git a/src/harness/opencode.ts b/src/harness/opencode.ts
index a6ad6eb..95d7f29 100644
--- a/src/harness/opencode.ts
+++ b/src/harness/opencode.ts
@@ -117,6 +117,12 @@ function isRecord(value: unknown): value is Record<string, unknown> {
   return !!value && typeof value === "object" && !Array.isArray(value);
 }
 
+function sessionCostUsd(session: OpenCodeSession | undefined): number {
+  return typeof session?.cost === "number" && Number.isFinite(session.cost) && session.cost >= 0
+    ? session.cost
+    : 0;
+}
+
 function extractPromptText(message: unknown): string {
   if (typeof message === "string") return message;
   if (!isRecord(message)) return String(message);
@@ -792,11 +798,12 @@ export class OpenCodeHarness implements AgentHarness {
       success: boolean,
       outcome: "completed" | "failed" | "interrupted",
       result?: string,
+      totalCostUsd = 0,
     ): boolean => emitRunCompleted({
       success,
       outcome,
       duration_ms: 0,
-      total_cost_usd: 0,
+      total_cost_usd: totalCostUsd,
       num_turns: runCounter,
       result,
       session_id: sessionId ?? "",
@@ -894,7 +901,7 @@ export class OpenCodeHarness implements AgentHarness {
           : `${event.type} failed`;
         if (turnInProgress && !turnWaitCompleted) {
           activeWaitController?.abort();
-          finishTurn(false, "failed", reason);
+          await completeTurn(false, reason);
         }
         return;
       }
@@ -957,10 +964,10 @@ export class OpenCodeHarness implements AgentHarness {
       if (streamStarted || !client) return;
       streamStarted = true;
       void client.streamEvents(handleEvent, streamController.signal)
-        .catch((error) => {
+        .catch(async (error) => {
           if (!streamController.signal.aborted && turnInProgress && !turnWaitCompleted) {
             activeWaitController?.abort();
-            finishTurn(false, "failed", errorMessage(error));
+            await completeTurn(false, errorMessage(error));
           }
         })
         .finally(() => {
@@ -972,6 +979,10 @@ export class OpenCodeHarness implements AgentHarness {
       return await http.request<unknown>("GET", `/session/${encodeURIComponent(id)}/message`);
     };
 
+    const fetchSession = async (http: OpenCodeClient, id: string): Promise<OpenCodeSession> => {
+      return await http.request<OpenCodeSession>("GET", `/session/${encodeURIComponent(id)}`);
+    };
+
     const sendPrompt = async (http: OpenCodeClient, id: string, text: string, promptSystemPrompt: string | undefined, signal: AbortSignal): Promise<void> => {
       await http.request("POST", `/session/${encodeURIComponent(id)}/prompt_async`, classicPromptBody(text, options.model, promptSystemPrompt), { signal });
     };
@@ -1064,12 +1075,18 @@ export class OpenCodeHarness implements AgentHarness {
 
     const completeTurn = async (success: boolean, result?: string, outcome: "completed" | "failed" | "interrupted" = success ? "completed" : "failed"): Promise<void> => {
       let finalResult = result;
-      if (success && client && sessionId) {
-        const messages = await fetchSessionMessages(client, sessionId)
-          .catch((): undefined => undefined);
+      let totalCostUsd = 0;
+      if (client && sessionId) {
+        const [messages, session] = await Promise.all([
+          success
+            ? fetchSessionMessages(client, sessionId).catch((): undefined => undefined)
+            : Promise.resolve(undefined),
+          fetchSession(client, sessionId).catch((): undefined => undefined),
+        ]);
         finalResult = finalResult ?? extractAssistantResult(messages);
+        totalCostUsd = sessionCostUsd(session);
       }
-      finishTurn(success, outcome, finalResult);
+      finishTurn(success, outcome, finalResult, totalCostUsd);
     };
 
     const runTurn = async (text: string): Promise<void> => {
@@ -1097,7 +1114,11 @@ export class OpenCodeHarness implements AgentHarness {
         await completeTurn(true);
       } catch (error) {
         activeWaitController = undefined;
-        await completeTurn(false, errorMessage(error));
+        if (sessionInterrupted) {
+          await completeTurn(false, undefined, "interrupted");
+        } else {
+          await completeTurn(false, errorMessage(error));
+        }
       } finally {
         turnInProgress = false;
         turnWaitCompleted = false;
@@ -1163,7 +1184,7 @@ export class OpenCodeHarness implements AgentHarness {
       } catch (error) {
         if (!sessionInterrupted) {
           if (!turnInProgress) turnCompletionEmitted = false;
-          finishTurn(false, "failed", errorMessage(error));
+          await completeTurn(false, errorMessage(error));
         }
       } finally {
         streamController.abort();
@@ -1221,14 +1242,18 @@ export class OpenCodeHarness implements AgentHarness {
         if (!turnInProgress) {
           turnCompletionEmitted = false;
         }
-        finishTurn(false, "interrupted");
         if (!client) {
+          finishTurn(false, "interrupted");
           await server?.close().catch((): undefined => undefined);
           return;
         }
-        if (!sessionId) return;
+        if (!sessionId) {
+          finishTurn(false, "interrupted");
+          return;
+        }
         const abortRequest = client.request("POST", `/session/${encodeURIComponent(sessionId)}/abort`).catch((): undefined => undefined);
         await abortRequest;
+        await completeTurn(false, undefined, "interrupted");
       },
     };
   }
diff --git a/tests/opencode-harness.test.ts b/tests/opencode-harness.test.ts
index 9038883..1cd0e50 100644
--- a/tests/opencode-harness.test.ts
+++ b/tests/opencode-harness.test.ts
@@ -15,6 +15,7 @@ type RequestRecord = {
 class MockOpenCodeServer {
   requests: RequestRecord[] = [];
   closed = false;
+  sessionCost = 0;
   waitMode: "immediate" | "defer" = "immediate";
   statusMode: "idle" | "busy-then-idle" | "always-busy" | "timeout" = "idle";
   busyStatusResponses = 0;
@@ -54,6 +55,9 @@ class MockOpenCodeServer {
     if (path === "/api/health") return json({ healthy: true, version: "1.16.2" });
     if (method === "POST" && path === "/session") return json({ id: "ses_test" });
     if (method === "POST" && path === "/session/ses_existing/fork") return json({ id: "ses_forked" });
+    if (method === "GET" && /^\/session\/ses_[^/]+$/.test(path)) {
+      return json({ id: path.slice("/session/".length), cost: this.sessionCost });
+    }
     if (method === "GET" && path === "/session/status") {
       this.statusRequests += 1;
       if (this.statusMode === "timeout") {
@@ -288,6 +292,25 @@ describe("OpenCodeHarness HTTP/SSE mapping", () => {
     assert.equal(mock.closed, true);
   });
 
+  it("reports OpenCode's persisted cumulative session cost", async () => {
+    const mock = new MockOpenCodeServer();
+    mock.sessionCost = 41.5661305;
+    const harness = new OpenCodeHarness({
+      createServer: async () => mock.handle(),
+      fetch: mock.fetch,
+    });
+
+    const messages = await collectMessages(harness.launch({
+      prompt: "ship it",
+      cwd: "/repo",
+    }));
+
+    const result = messages.find((message) => message.type === "run_completed") as Extract<HarnessMessage, { type: "run_completed" }> | undefined;
+    assert.equal(result?.data.success, true);
+    assert.equal(result?.data.total_cost_usd, 41.5661305);
+    assert.equal(mock.requests.some((request) => request.method === "GET" && request.path === "/session/ses_test"), true);
+  });
+
   it("uses the real OpenCode classic JSON lifecycle endpoints", async () => {
     const mock = new MockOpenCodeServer();
     const harness = new OpenCodeHarness({
@@ -310,6 +333,7 @@ describe("OpenCodeHarness HTTP/SSE mapping", () => {
       "/session",
       "/session/ses_test/message",
       "/session/ses_test/prompt_async",
+      "/session/ses_test",
       "/session/status",
     ]));
   });