diff --git a/packages/server/src/server/agent/providers/opencode-agent.slash-command-timeout.test.ts b/packages/server/src/server/agent/providers/opencode-agent.slash-command-timeout.test.ts
new file mode 100644
index 000000000..a57590f38
--- /dev/null
+++ b/packages/server/src/server/agent/providers/opencode-agent.slash-command-timeout.test.ts
@@ -0,0 +1,86 @@
+import { afterEach, describe, expect, test, vi } from "vitest";
+
+vi.mock("@opencode-ai/sdk/v2/client", () => ({
+  createOpencodeClient: vi.fn(),
+}));
+
+import { createOpencodeClient } from "@opencode-ai/sdk/v2/client";
+
+import { createTestLogger } from "../../../test-utils/test-logger.js";
+import { OpenCodeAgentClient, OpenCodeServerManager } from "./opencode-agent.js";
+
+function createDeferred<T>(): {
+  promise: Promise<T>;
+  resolve: (value: T) => void;
+  reject: (error: unknown) => void;
+} {
+  let resolve!: (value: T) => void;
+  let reject!: (error: unknown) => void;
+  const promise = new Promise<T>((res, rej) => {
+    resolve = res;
+    reject = rej;
+  });
+  return { promise, resolve, reject };
+}
+
+describe("OpenCodeAgentSession slash command timeout handling", () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  test("waits for SSE completion when slash commands hit a header timeout", async () => {
+    const idleEventGate = createDeferred<void>();
+
+    vi.mocked(createOpencodeClient).mockReturnValue({
+      session: {
+        create: vi.fn().mockResolvedValue({ data: { id: "session-1" } }),
+        command: vi.fn().mockRejectedValue(new Error("fetch failed: Headers Timeout Error")),
+      },
+      provider: {
+        list: vi.fn().mockResolvedValue({
+          data: {
+            connected: ["openai"],
+            all: [{ id: "openai", name: "OpenAI", models: {} }],
+          },
+        }),
+      },
+      event: {
+        subscribe: vi.fn().mockResolvedValue({
+          stream: (async function* () {
+            await idleEventGate.promise;
+            yield {
+              type: "session.idle",
+              properties: { sessionID: "session-1" },
+            };
+          })(),
+        }),
+      },
+      command: {
+        list: vi.fn().mockResolvedValue({
+          data: [{ name: "help", description: "Show help", hints: [] }],
+        }),
+      },
+      app: {
+        agents: vi.fn().mockResolvedValue({ data: [] }),
+      },
+    } as never);
+
+    vi.spyOn(OpenCodeServerManager, "getInstance").mockReturnValue({
+      ensureRunning: vi.fn().mockResolvedValue({ port: 1234, url: "http://127.0.0.1:1234" }),
+    } as never);
+
+    const client = new OpenCodeAgentClient(createTestLogger());
+    const session = await client.createSession({ provider: "opencode", cwd: "/tmp" });
+
+    const runPromise = session.run("/help");
+    await Promise.resolve();
+    idleEventGate.resolve();
+
+    await expect(runPromise).resolves.toMatchObject({
+      sessionId: "session-1",
+      finalText: "",
+      timeline: [],
+      usage: undefined,
+    });
+  });
+});
diff --git a/packages/server/src/server/agent/providers/opencode-agent.ts b/packages/server/src/server/agent/providers/opencode-agent.ts
index 3e036bd8c..4aea0eb2e 100644
--- a/packages/server/src/server/agent/providers/opencode-agent.ts
+++ b/packages/server/src/server/agent/providers/opencode-agent.ts
@@ -107,6 +107,12 @@ const OPENCODE_FATAL_RETRY_MESSAGE_TOKENS = [
   "does not exist",
   "unsupported model",
 ] as const;
+const OPENCODE_HEADERS_TIMEOUT_TOKENS = [
+  "headers timeout",
+  "headers timeout error",
+  "headers_timeout",
+  "und_err_headers_timeout",
+] as const;
 
 const OpencodeToolStateSchema = z
   .object({
@@ -306,6 +312,49 @@ function isFatalOpenCodeRetryMessage(message: string | null | undefined): boolea
   return OPENCODE_FATAL_RETRY_MESSAGE_TOKENS.some((token) => normalized.includes(token));
 }
 
+function isOpenCodeHeadersTimeoutFailure(error: unknown): boolean {
+  const diagnostics = new Set<string>();
+  const queue: unknown[] = [error];
+
+  while (queue.length > 0) {
+    const current = queue.shift();
+    if (!current) {
+      continue;
+    }
+
+    const normalized = stringifyUnknownError(current).trim().toLowerCase();
+    if (normalized) {
+      diagnostics.add(normalized);
+    }
+
+    if (typeof current === "object") {
+      const record = current as {
+        message?: unknown;
+        code?: unknown;
+        name?: unknown;
+        cause?: unknown;
+      };
+
+      for (const value of [record.message, record.code, record.name]) {
+        if (typeof value === "string") {
+          const diagnostic = value.trim().toLowerCase();
+          if (diagnostic) {
+            diagnostics.add(diagnostic);
+          }
+        }
+      }
+
+      if (record.cause) {
+        queue.push(record.cause);
+      }
+    }
+  }
+
+  return [...diagnostics].some((diagnostic) =>
+    OPENCODE_HEADERS_TIMEOUT_TOKENS.some((token) => diagnostic.includes(token)),
+  );
+}
+
 function isAlreadyPresentMcpError(error: unknown): boolean {
   const normalized = stringifyUnknownError(error).toLowerCase();
   return MCP_ALREADY_PRESENT_ERROR_TOKENS.some((token) => normalized.includes(token));
@@ -1598,6 +1647,17 @@ class OpenCodeAgentSession implements AgentSession {
         })
         .then((response) => {
           if (response.error) {
+            if (isOpenCodeHeadersTimeoutFailure(response.error)) {
+              this.logger.warn(
+                {
+                  err: response.error,
+                  commandName: slashCommand.commandName,
+                  turnId,
+                },
+                "OpenCode slash command hit a header timeout; waiting for SSE terminal event",
+              );
+              return;
+            }
             const errorMsg = normalizeTurnFailureError(response.error);
             this.finishForegroundTurn(
               { type: "turn_failed", provider: "opencode", error: errorMsg },
@@ -1611,6 +1671,17 @@ class OpenCodeAgentSession implements AgentSession {
           }
         })
         .catch((err) => {
+          if (isOpenCodeHeadersTimeoutFailure(err)) {
+            this.logger.warn(
+              {
+                err,
+                commandName: slashCommand.commandName,
+                turnId,
+              },
+              "OpenCode slash command hit a header timeout; waiting for SSE terminal event",
+            );
+            return;
+          }
           this.finishForegroundTurn(
             { type: "turn_failed", provider: "opencode", error: normalizeTurnFailureError(err) },
             turnId,