fix(server): stop sending the local directory to a remote OpenCode server

apps/server/src/provider/Drivers/OpenCodeDriver.ts

@@ -180,6 +180,7 @@ export const OpenCodeDriver: ProviderDriver<OpenCodeSettings, OpenCodeDriverEnv>
                 const client = openCodeRuntime.createOpenCodeSdkClient({
                   baseUrl: server.url,
                   directory: cwd,
+                  external: server.external,
                   ...(effectiveConfig.serverPassword
                     ? { serverPassword: effectiveConfig.serverPassword }
                     : {}),
@@ -192,6 +193,7 @@ export const OpenCodeDriver: ProviderDriver<OpenCodeSettings, OpenCodeDriverEnv>
                 openCodeRuntime.createOpenCodeSdkClient({
                   baseUrl: server.url,
                   directory: cwd,
+                  external: false,
                   ...(server.serverPassword !== undefined
                     ? { serverPassword: server.serverPassword }
                     : {}),

apps/server/src/provider/Layers/OpenCodeAdapter.test.ts

@@ -535,6 +535,13 @@ const openCodeAdapterTestSettings = Schema.decodeSync(OpenCodeSettings)({
   serverPassword: "secret-password",
 });
 
+// A non-loopback server URL, so the adapter treats the session as remote.
+const openCodeAdapterRemoteSettings = Schema.decodeSync(OpenCodeSettings)({
+  binaryPath: "fake-opencode",
+  serverUrl: "http://10.0.0.5:4096",
+  serverPassword: "secret-password",
+});
+
 const OpenCodeAdapterTestLayer = Layer.effect(
   OpenCodeAdapter,
   makeOpenCodeAdapter(openCodeAdapterTestSettings),
@@ -1240,6 +1247,57 @@ it.layer(OpenCodeAdapterTestLayer)("OpenCodeAdapterLive", (it) => {
     }),
   );
 
+  it.effect(
+    "reuses a remote session without forking even when the server directory differs",
+    () => {
+      const remoteLayer = Layer.effect(
+        OpenCodeAdapter,
+        makeOpenCodeAdapter(openCodeAdapterRemoteSettings),
+      ).pipe(
+        Layer.provideMerge(Layer.succeed(OpenCodeRuntime, OpenCodeRuntimeTestDouble)),
+        Layer.provideMerge(ServerConfig.layerTest(process.cwd(), process.cwd())),
+        Layer.provideMerge(
+          ServerSettingsService.layerTest({
+            providers: {
+              opencode: {
+                binaryPath: "fake-opencode",
+                serverUrl: "http://10.0.0.5:4096",
+                serverPassword: "secret-password",
+              },
+            },
+          }),
+        ),
+        Layer.provideMerge(providerSessionDirectoryTestLayer),
+        Layer.provideMerge(NodeServices.layer),
+      );
+
+      return Effect.gen(function* () {
+        const adapter = yield* OpenCodeAdapter;
+        // The server-side directory differs from this test's local cwd.
+        runtimeMock.state.sessionDirectoryById.set("ses_remote", "/var/log");
+
+        const session = yield* adapter.startSession({
+          provider: ProviderDriverKind.make("opencode"),
+          threadId: asThreadId("thread-opencode-remote-reuse"),
+          runtimeMode: "full-access",
+          resumeCursor: { schemaVersion: 1, sessionId: "ses_remote" },
+        });
+
+        NodeAssert.deepEqual(runtimeMock.state.sessionGetIds, ["ses_remote"]);
+        NodeAssert.deepEqual(runtimeMock.state.sessionCreateUrls, []);
+        NodeAssert.deepEqual(runtimeMock.state.forkCalls, []);
+        NodeAssert.deepEqual(session.resumeCursor, {
+          schemaVersion: 1,
+          sessionId: "ses_remote",
+        });
+        NodeAssert.equal(runtimeMock.state.sessionUpdateCalls.length, 1);
+        NodeAssert.equal(runtimeMock.state.sessionUpdateCalls[0]?.sessionID, "ses_remote");
+
+        yield* adapter.stopSession(asThreadId("thread-opencode-remote-reuse"));
+      }).pipe(Effect.provide(remoteLayer));
+    },
+  );
+
   it.effect("fails sendTurn for missing sessions through the typed error channel", () =>
     Effect.gen(function* () {
       const adapter = yield* OpenCodeAdapter;

apps/server/src/provider/Layers/OpenCodeAdapter.ts

@@ -46,6 +46,7 @@ import { buildRuntimeInstructions } from "../RuntimeInstructions.ts";
 import { type OpenCodeAdapterShape } from "../Services/OpenCodeAdapter.ts";
 import {
   buildOpenCodePermissionRules,
+  isLoopbackBaseUrl,
   OpenCodeRuntime,
   OpenCodeRuntimeError,
   openCodeQuestionId,
@@ -2811,6 +2812,7 @@ export function makeOpenCodeAdapter(
               const client = openCodeRuntime.createOpenCodeSdkClient({
                 baseUrl: server.url,
                 directory,
+                external: server.external,
                 ...(server.serverPassword ? { serverPassword: server.serverPassword } : {}),
               });
               const mcpSession = McpProviderSession.readMcpProviderSession(input.threadId);
@@ -2845,12 +2847,16 @@ export function makeOpenCodeAdapter(
                       ),
                     )
                   : undefined;
+                // Non-loopback external servers retain their own session directory.
+                const isRemote = server.external && !isLoopbackBaseUrl(server.url);
 
-                // Reuse in place only when the session still matches the
-                // requested cwd; on a cwd change it is forked below instead.
+                // Remote sessions keep their server-side cwd. Local sessions need a
+                // matching cwd to be reused; otherwise they are forked below.
                 const reusable =
                   adopted &&
-                  (!adopted.directory || (yield* sameDirectory(adopted.directory, directory)))
+                  (isRemote ||
+                    !adopted.directory ||
+                    (yield* sameDirectory(adopted.directory, directory)))
                     ? adopted
                     : undefined;
 
@@ -2871,7 +2877,7 @@ export function makeOpenCodeAdapter(
                 // moved into a git worktree). Fork it into the requested
                 // directory instead of minting an empty one — the fork carries
                 // the full history, so the follow-up keeps its context (#3604).
-                if (adopted) {
+                if (adopted && !isRemote) {
                   yield* Effect.logInfo(
                     `OpenCode session '${adopted.id}' was created under a different working directory; forking into '${directory}' to preserve conversation history.`,
                   );

apps/server/src/provider/Layers/OpenCodeProvider.test.ts

@@ -45,6 +45,7 @@ const runtimeMock = {
     sdkClientInputs: [] as Array<{
       baseUrl: string;
       directory: string;
+      external: boolean;
       serverPassword?: string;
     }>,
     inventory: {
@@ -372,6 +373,7 @@ it.layer(testLayer)("checkOpenCodeProviderStatus", (it) => {
         {
           baseUrl: "http://127.0.0.1:4301",
           directory: process.cwd(),
+          external: false,
           serverPassword: "secret-password",
         },
       ]);
@@ -390,6 +392,7 @@ it.layer(testLayer)("checkOpenCodeProviderStatus", (it) => {
         {
           baseUrl: "http://127.0.0.1:4301",
           directory: process.cwd(),
+          external: false,
           serverPassword: "environment-password",
         },
       ]);
@@ -438,6 +441,7 @@ it.layer(testLayer)("checkOpenCodeProviderStatus with configured server URL", (i
         {
           baseUrl: "http://127.0.0.1:9999",
           directory: process.cwd(),
+          external: true,
         },
       ]);
     }),

apps/server/src/provider/Layers/OpenCodeProvider.ts

@@ -478,12 +478,14 @@ export const checkOpenCodeProviderStatus = Effect.fn("checkOpenCodeProviderStatu
     readonly url: string;
     readonly serverPassword?: string;
     readonly version: string;
+    readonly external?: boolean;
   }) =>
     openCodeRuntime
       .loadOpenCodeInventory(
         openCodeRuntime.createOpenCodeSdkClient({
           baseUrl: server.url,
           directory: cwd,
+          external: server.external ?? false,
           ...(server.serverPassword !== undefined ? { serverPassword: server.serverPassword } : {}),
         }),
       )