fix: avoid embedded opencode port conflicts

src/runtime/opencode.ts

@@ -4,6 +4,7 @@ import {
   type OpencodeClient,
 } from "@opencode-ai/sdk/v2";
 import { existsSync, readFileSync } from "node:fs";
+import { createServer } from "node:net";
 import { resolve } from "node:path";
 
 import { config } from "../config.js";
@@ -44,6 +45,34 @@ type RuntimeMessage = {
 const getRuntimeMessageRole = (message: RuntimeMessage) => message.info.role;
 const getRuntimeMessageId = (message: RuntimeMessage) => message.info.id;
 
+const isTcpPortAvailable = (hostname: string, port: number) =>
+  new Promise<boolean>((resolve, reject) => {
+    const server = createServer();
+    server.unref();
+    server.once("error", (error: NodeJS.ErrnoException) => {
+      if (error.code === "EADDRINUSE") {
+        resolve(false);
+        return;
+      }
+      reject(error);
+    });
+    server.listen({ host: hostname, port, exclusive: true }, () => {
+      server.close((error) => (error ? reject(error) : resolve(true)));
+    });
+  });
+
+export const resolveEmbeddedOpencodePort = async (
+  hostname: string,
+  configuredPort: number,
+) => {
+  if (configuredPort === 0) {
+    return 0;
+  }
+  return (await isTcpPortAvailable(hostname, configuredPort))
+    ? configuredPort
+    : 0;
+};
+
 export class OpencodeRuntimeAdapter {
   private clientPromise: Promise<OpencodeClient> | null = null;
   private closeServer: (() => void) | null = null;
@@ -408,10 +437,24 @@ export class OpencodeRuntimeAdapter {
       process.env.TJWATER_AGENT_INTERNAL_TOKEN ??
       "";
 
+    const port = await resolveEmbeddedOpencodePort(
+      config.OPENCODE_HOSTNAME,
+      config.OPENCODE_PORT,
+    );
+    if (port !== config.OPENCODE_PORT) {
+      logger.warn(
+        {
+          hostname: config.OPENCODE_HOSTNAME,
+          configuredPort: config.OPENCODE_PORT,
+        },
+        "configured opencode port is occupied; falling back to a dynamic port",
+      );
+    }
+
     logger.info(
       {
         hostname: config.OPENCODE_HOSTNAME,
-        port: config.OPENCODE_PORT,
+        port,
         model: config.OPENCODE_MODEL,
         mode: config.OPENCODE_MODE,
       },
@@ -423,7 +466,7 @@ export class OpencodeRuntimeAdapter {
     try {
       runtime = await createOpencode({
         hostname: config.OPENCODE_HOSTNAME,
-        port: config.OPENCODE_PORT,
+        port,
         timeout: config.OPENCODE_TIMEOUT_MS,
         config: buildOpencodeConfig(),
       });
@@ -440,7 +483,7 @@ export class OpencodeRuntimeAdapter {
       {
         elapsedMs: Math.max(0, Date.now() - startedAt),
         hostname: config.OPENCODE_HOSTNAME,
-        port: config.OPENCODE_PORT,
+        baseUrl: runtime.server.url,
         mode: config.OPENCODE_MODE,
       },
       "opencode server started in embedded mode",