diff --git a/plugins/opencode/scripts/lib/opencode-server.mjs b/plugins/opencode/scripts/lib/opencode-server.mjs
index c2bb308..4935cfc 100644
--- a/plugins/opencode/scripts/lib/opencode-server.mjs
+++ b/plugins/opencode/scripts/lib/opencode-server.mjs
@@ -22,6 +22,7 @@
 import crypto from "node:crypto";
 import os from "node:os";
 import { spawn } from "node:child_process";
+import http from "node:http";
 import fs from "node:fs";
 import path from "node:path";
 import { platformShellOption, isProcessAlive as isProcessAliveWithToken } from "./process.mjs";
@@ -32,6 +33,102 @@ const DEFAULT_HOST = "127.0.0.1";
 const SERVER_START_TIMEOUT = 30_000;
 const SERVER_REAP_IDLE_TIMEOUT = 5 * 60 * 1000; // 5 minutes
 
+// Wall-clock budget for a single `sendPrompt` call. Must be longer than
+// any single model turn the user can realistically wait for, but bounded
+// so a wedged socket can't hang the companion forever. Overridable via
+// OPENCODE_COMPANION_PROMPT_TIMEOUT_MS. The tracked-jobs layer has its
+// own 30 min hard timer (OPENCODE_COMPANION_JOB_TIMEOUT_MS) on top of
+// this — this constant is the per-HTTP-call fallback, not the
+// authoritative cap.
+const DEFAULT_PROMPT_TIMEOUT_MS = 30 * 60 * 1000;
+
+function resolvePromptTimeoutMs() {
+  const fromEnv = Number(process.env.OPENCODE_COMPANION_PROMPT_TIMEOUT_MS);
+  if (Number.isFinite(fromEnv) && fromEnv > 0) return fromEnv;
+  return DEFAULT_PROMPT_TIMEOUT_MS;
+}
+
+/**
+ * POST a JSON body via `node:http` and return the parsed response.
+ *
+ * We deliberately avoid `fetch()` here because Node's bundled undici
+ * imposes a 300_000 ms default `bodyTimeout` that surfaces as
+ * `TypeError: terminated` when the OpenCode server holds the connection
+ * open mid-body for longer than 5 minutes — which is the normal case
+ * for long adversarial reviews against slow/free models. `node:http`
+ * has no such default, so this helper only enforces the explicit
+ * wall-clock timer we pass in.
+ *
+ * See issue: "OpenCode adversarial review failed: terminated" (fetch
+ * failed ~4.5 min into a run). The outer `AbortSignal.timeout()` we
+ * used before was a wall-clock abort, not a dispatcher-level body
+ * timeout, so it did not prevent undici from killing the socket first.
+ *
+ * @param {string} urlString Absolute URL to POST to.
+ * @param {Record<string,string>} headers
+ * @param {unknown} bodyObj JSON-serializable body.
+ * @param {{ timeoutMs?: number }} [opts]
+ * @returns {Promise<{ status: number, body: string }>}
+ */
+function httpPostJson(urlString, headers, bodyObj, opts = {}) {
+  const timeoutMs = Number.isFinite(opts.timeoutMs) && opts.timeoutMs > 0
+    ? opts.timeoutMs
+    : resolvePromptTimeoutMs();
+  const url = new URL(urlString);
+  const payload = Buffer.from(JSON.stringify(bodyObj), "utf8");
+
+  return new Promise((resolve, reject) => {
+    let settled = false;
+    const finish = (fn, val) => {
+      if (settled) return;
+      settled = true;
+      clearTimeout(timer);
+      fn(val);
+    };
+
+    const req = http.request(
+      {
+        protocol: url.protocol,
+        host: url.hostname,
+        port: url.port || (url.protocol === "https:" ? 443 : 80),
+        method: "POST",
+        path: `${url.pathname}${url.search}`,
+        headers: {
+          ...headers,
+          "Content-Length": payload.length,
+        },
+      },
+      (res) => {
+        let data = "";
+        res.setEncoding("utf8");
+        res.on("data", (chunk) => {
+          data += chunk;
+        });
+        res.on("end", () => {
+          finish(resolve, { status: res.statusCode ?? 0, body: data });
+        });
+        res.on("error", (err) => finish(reject, err));
+      }
+    );
+
+    req.on("error", (err) => finish(reject, err));
+
+    const timer = setTimeout(() => {
+      finish(
+        reject,
+        new Error(
+          `OpenCode prompt exceeded ${Math.round(timeoutMs / 1000)}s wall-clock timeout ` +
+            `(set OPENCODE_COMPANION_PROMPT_TIMEOUT_MS to raise)`
+        )
+      );
+      req.destroy();
+    }, timeoutMs);
+
+    req.write(payload);
+    req.end();
+  });
+}
+
 function serverStatePath(workspacePath) {
   const key = typeof workspacePath === "string" && workspacePath.length > 0 ? workspacePath : process.cwd();
   const hash = crypto.createHash("sha256").update(key).digest("hex").slice(0, 16);
@@ -255,6 +352,11 @@ export function createClient(baseUrl, opts = {}) {
     /**
      * Send a prompt (synchronous / streaming).
      * Returns the full response text from SSE stream.
+     *
+     * Uses `node:http` directly (via `httpPostJson`) instead of `fetch()`
+     * because Node's bundled undici has a hidden 300_000 ms default
+     * `bodyTimeout` that surfaces as `TypeError: terminated` on long
+     * reviews — see the helper for details.
      */
     sendPrompt: async (sessionId, promptText, opts = {}) => {
       const body = {
@@ -268,19 +370,23 @@ export function createClient(baseUrl, opts = {}) {
       // the custom `review` agent isn't available on a pre-running server.
       if (opts.tools) body.tools = opts.tools;
 
-      const res = await fetch(`${baseUrl}/session/${sessionId}/message`, {
-        method: "POST",
+      const { status, body: responseText } = await httpPostJson(
+        `${baseUrl}/session/${sessionId}/message`,
         headers,
-        body: JSON.stringify(body),
-        signal: AbortSignal.timeout(600_000), // 10 min for long tasks
-      });
+        body
+      );
 
-      if (!res.ok) {
-        const text = await res.text().catch(() => "");
-        throw new Error(`OpenCode prompt failed ${res.status}: ${text}`);
+      if (status < 200 || status >= 300) {
+        throw new Error(`OpenCode prompt failed ${status}: ${responseText}`);
       }
 
-      return res.json();
+      try {
+        return JSON.parse(responseText);
+      } catch (err) {
+        throw new Error(
+          `OpenCode prompt returned non-JSON response (${status}): ${err.message}`
+        );
+      }
     },
 
     /**
diff --git a/tests/send-prompt-body-timeout.test.mjs b/tests/send-prompt-body-timeout.test.mjs
new file mode 100644
index 0000000..4cebc74
--- /dev/null
+++ b/tests/send-prompt-body-timeout.test.mjs
@@ -0,0 +1,76 @@
+// Regression test for the undici `bodyTimeout` bug that made long
+// adversarial reviews die with `TypeError: terminated` around the
+// 4.5–5 minute mark.
+//
+// Node's bundled undici has a 300_000 ms default `bodyTimeout` that
+// fires when the server holds the connection open mid-body longer than
+// 5 minutes. The OpenCode `/session/{id}/message` endpoint legitimately
+// does exactly that while the model thinks on a long review. Our
+// `sendPrompt` used to be built on `fetch()` and was subject to this
+// hidden timer; it now uses `node:http` directly so no dispatcher-level
+// body timer can pull the rug out from under us.
+//
+// We don't actually wait 5 minutes in the test — we stall the server
+// for 7 seconds, which is far longer than any `fetch()`-based
+// implementation could be configured to tolerate without importing
+// `undici` explicitly (which we refuse to do because it's not an
+// installed dependency). 7 s is enough to prove the request is not
+// being cut off by a short internal timer while still keeping `npm
+// test` fast.
+
+import { describe, it, before, after } from "node:test";
+import assert from "node:assert/strict";
+import http from "node:http";
+import { createClient } from "../plugins/opencode/scripts/lib/opencode-server.mjs";
+
+describe("sendPrompt body-timeout resilience", () => {
+  /** @type {http.Server} */
+  let server;
+  let baseUrl;
+
+  before(async () => {
+    server = http.createServer((req, res) => {
+      if (req.url !== "/session/stall-test/message") {
+        res.writeHead(404).end();
+        return;
+      }
+      // Drain the request body, then begin a chunked response and stall
+      // for several seconds before completing it. This simulates
+      // OpenCode holding the connection open while the model thinks.
+      req.on("data", () => {});
+      req.on("end", () => {
+        res.writeHead(200, {
+          "Content-Type": "application/json",
+          "Transfer-Encoding": "chunked",
+        });
+        res.write("{");
+        setTimeout(() => {
+          res.end('"ok":true}');
+        }, 7_000);
+      });
+    });
+    await new Promise((resolve) => server.listen(0, "127.0.0.1", resolve));
+    const addr = server.address();
+    baseUrl = `http://127.0.0.1:${addr.port}`;
+  });
+
+  after(async () => {
+    await new Promise((resolve) => server.close(resolve));
+  });
+
+  it(
+    "tolerates a server that holds the response body for 7+ seconds",
+    { timeout: 20_000 },
+    async () => {
+      const client = createClient(baseUrl);
+      const start = Date.now();
+      const result = await client.sendPrompt("stall-test", "hello");
+      const elapsedMs = Date.now() - start;
+      assert.deepEqual(result, { ok: true });
+      assert.ok(
+        elapsedMs >= 6_500,
+        `expected request to take ~7s, actually took ${elapsedMs}ms`
+      );
+    }
+  );
+});