diff --git a/server/packages/sandbox-agent/src/cli.rs b/server/packages/sandbox-agent/src/cli.rs
index 8ca965f..27fb545 100644
--- a/server/packages/sandbox-agent/src/cli.rs
+++ b/server/packages/sandbox-agent/src/cli.rs
@@ -620,14 +620,20 @@ fn run_opencode(cli: &CliConfig, args: &OpencodeArgs) -> Result<(), CliError> {
     crate::daemon::ensure_running(cli, &args.host, args.port, token.as_deref())?;
     write_stderr_line("gigacode startup: daemon is healthy")?;
 
-    write_stderr_line("gigacode startup: creating OpenCode session via /opencode/session")?;
-    let session_id = create_opencode_session(
-        &base_url,
-        token.as_deref(),
-        args.session_title.as_deref(),
-        yolo,
-    )?;
-    write_stdout_line(&format!("OpenCode session: {session_id}"))?;
+    let attach_session_id = if args.session_title.is_some() || yolo {
+        write_stderr_line("gigacode startup: creating OpenCode session via /opencode/session")?;
+        let session_id = create_opencode_session(
+            &base_url,
+            token.as_deref(),
+            args.session_title.as_deref(),
+            yolo,
+        )?;
+        write_stdout_line(&format!("OpenCode session: {session_id}"))?;
+        Some(session_id)
+    } else {
+        write_stderr_line("gigacode startup: attaching OpenCode without precreating a session")?;
+        None
+    };
 
     let attach_url = format!("{base_url}/opencode");
     write_stderr_line("gigacode startup: resolving OpenCode binary (installing if needed)")?;
@@ -640,11 +646,12 @@ fn run_opencode(cli: &CliConfig, args: &OpencodeArgs) -> Result<(), CliError> {
     opencode_cmd
         .arg("attach")
         .arg(&attach_url)
-        .arg("--session")
-        .arg(&session_id)
         .stdin(Stdio::inherit())
         .stdout(Stdio::inherit())
         .stderr(Stdio::inherit());
+    if let Some(session_id) = attach_session_id.as_deref() {
+        opencode_cmd.arg("--session").arg(session_id);
+    }
     if let Some(token) = token.as_deref() {
         opencode_cmd.arg("--password").arg(token);
     }
diff --git a/server/packages/sandbox-agent/src/opencode_compat.rs b/server/packages/sandbox-agent/src/opencode_compat.rs
index 1852a20..e6ee2aa 100644
--- a/server/packages/sandbox-agent/src/opencode_compat.rs
+++ b/server/packages/sandbox-agent/src/opencode_compat.rs
@@ -3796,10 +3796,20 @@ async fn oc_session_create(
 async fn oc_session_list(State(state): State<Arc<OpenCodeAppState>>) -> impl IntoResponse {
     let sessions = state.inner.session_manager().list_sessions().await;
     let project_id = &state.opencode.default_project_id;
-    let values: Vec<Value> = sessions
+    let mut values: Vec<Value> = sessions
         .iter()
         .map(|s| session_info_to_opencode_value(s, project_id))
         .collect();
+    let mut seen_session_ids: HashSet<String> = sessions
+        .iter()
+        .map(|session| session.session_id.clone())
+        .collect();
+    let compat_sessions = state.opencode.sessions.lock().await;
+    for (session_id, session) in compat_sessions.iter() {
+        if seen_session_ids.insert(session_id.clone()) {
+            values.push(session.to_value());
+        }
+    }
     (StatusCode::OK, Json(json!(values)))
 }
 
@@ -3829,6 +3839,10 @@ async fn oc_session_get(
         )
             .into_response();
     }
+    let sessions = state.opencode.sessions.lock().await;
+    if let Some(session) = sessions.get(&session_id) {
+        return (StatusCode::OK, Json(session.to_value())).into_response();
+    }
     not_found("Session not found").into_response()
 }
 
diff --git a/server/packages/sandbox-agent/tests/opencode-compat/session.test.ts b/server/packages/sandbox-agent/tests/opencode-compat/session.test.ts
index bdb1052..94c8762 100644
--- a/server/packages/sandbox-agent/tests/opencode-compat/session.test.ts
+++ b/server/packages/sandbox-agent/tests/opencode-compat/session.test.ts
@@ -291,6 +291,41 @@ describe("OpenCode-compatible Session API", () => {
       expect(response.data?.title).toBe("Test");
     });
 
+    it("should keep session.get available during first prompt after /new-style creation", async () => {
+      const providers = await getProvidersViaHttp();
+      const providerId = providers.connected.find(
+        (provider) => provider !== "mock" && typeof providers.default?.[provider] === "string"
+      );
+      if (!providerId) {
+        return;
+      }
+      const modelId = providers.default?.[providerId];
+      if (!modelId) {
+        return;
+      }
+
+      const created = await client.session.create({ body: { title: "Race Repro" } });
+      const sessionId = created.data?.id!;
+      expect(sessionId).toBeDefined();
+
+      const promptPromise = client.session.prompt({
+        path: { id: sessionId },
+        body: {
+          model: { providerID: providerId, modelID: modelId },
+          parts: [{ type: "text", text: "hello after /new" }],
+        },
+      });
+
+      await new Promise((resolve) => setTimeout(resolve, 25));
+
+      const getDuringPrompt = await client.session.get({ path: { id: sessionId } });
+      expect(getDuringPrompt.error).toBeUndefined();
+      expect(getDuringPrompt.data?.id).toBe(sessionId);
+
+      // Best-effort settle; this assertion focuses on availability during the in-flight turn.
+      await promptPromise;
+    });
+
     it("should return error for non-existent session", async () => {
       const response = await client.session.get({
         path: { id: "non-existent-session-id" },