diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index eb116f6b9..5182a706c 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -1108,9 +1108,22 @@ const layer = Layer.effect(
               (part) => part.type === "tool" && !part.metadata?.providerExecuted && !isOrphanedInterruptedTool(part),
             ) ?? false
 
+          // "unknown" is every mapper's fallback for a finish reason we could not
+          // interpret, and the AI SDK reports a stream that closed without any
+          // finish chunk at all as "other", which maps here too. Neither means the
+          // model was done, so resample the turn like "tool-calls" instead of
+          // exiting as a clean completion. Exiting here silently truncated runs
+          // mid-task: the error check below already excludes "unknown", so nothing
+          // was recorded anywhere.
+          if (lastAssistant?.finish === "unknown")
+            yield* Effect.logWarning("resampling turn that ended with an unmapped finish reason", {
+              "session.id": sessionID,
+              messageID: lastAssistant.id,
+            })
+
           if (
             lastAssistant?.finish &&
-            !["tool-calls"].includes(lastAssistant.finish) &&
+            !["tool-calls", "unknown"].includes(lastAssistant.finish) &&
             !hasToolCalls &&
             lastUser.id < lastAssistant.id
           ) {
diff --git a/packages/opencode/test/session/prompt.test.ts b/packages/opencode/test/session/prompt.test.ts
index 491ad06aa..2f815199b 100644
--- a/packages/opencode/test/session/prompt.test.ts
+++ b/packages/opencode/test/session/prompt.test.ts
@@ -810,6 +810,36 @@ it.instance("loop continues when finish is tool-calls", () =>
   }),
 )
 
+it.instance("loop resamples when the provider closes a stream without a finish reason", () =>
+  Effect.gen(function* () {
+    const { llm } = yield* useServerConfig(providerCfg)
+    const prompt = yield* SessionPrompt.Service
+    const sessions = yield* Session.Service
+    const session = yield* sessions.create({
+      title: "Pinned",
+      permission: [{ permission: "*", pattern: "*", action: "allow" }],
+    })
+    yield* prompt.prompt({
+      sessionID: session.id,
+      agent: "build",
+      noReply: true,
+      parts: [{ type: "text", text: "hello" }],
+    })
+    // No finish chunk: the AI SDK reports this as finishReason "other", which we
+    // map to "unknown". The loop must resample instead of ending the run.
+    yield* llm.push(reply().item())
+    yield* llm.text("second")
+
+    const result = yield* prompt.loop({ sessionID: session.id })
+    expect(yield* llm.calls).toBe(2)
+    expect(result.info.role).toBe("assistant")
+    if (result.info.role === "assistant") {
+      expect(result.parts.some((part) => part.type === "text" && part.text === "second")).toBe(true)
+      expect(result.info.finish).toBe("stop")
+    }
+  }),
+)
+
 it.instance("glob tool keeps instance context during prompt runs", () =>
   Effect.gen(function* () {
     const { dir, llm } = yield* useServerConfig(providerCfg)