diff --git a/crates/openshell-supervisor-network/src/proxy.rs b/crates/openshell-supervisor-network/src/proxy.rs
index 5f224b474e..6ac6628cc4 100644
--- a/crates/openshell-supervisor-network/src/proxy.rs
+++ b/crates/openshell-supervisor-network/src/proxy.rs
@@ -2455,13 +2455,24 @@ async fn handle_mediated_connection(
             return Ok(());
         }
 
-        let n = client.read(&mut buf[used..]).await.into_diagnostic()?;
-        if n == 0 {
+        // A mediated open's first workload bytes follow the synthesized CONNECT header.
+        // Take only the header out of the reader so the bytes behind it stay buffered for
+        // the relay; overlap three bytes so a terminator split across fills is found.
+        let available = client.fill_buf().await.into_diagnostic()?;
+        if available.is_empty() {
             return Ok(());
         }
-        used += n;
-
-        if buf[..used].windows(4).any(|win| win == b"\r\n\r\n") {
+        let n = available.len().min(buf.len() - used);
+        buf[used..used + n].copy_from_slice(&available[..n]);
+        let start = used.saturating_sub(3);
+        let end = buf[start..used + n]
+            .windows(4)
+            .position(|window| window == b"\r\n\r\n")
+            .map(|position| start + position + 4);
+        let consumed = end.map_or(n, |end| end - used);
+        client.consume(consumed);
+        used += consumed;
+        if end.is_some() {
             break;
         }
     }
@@ -7660,6 +7671,145 @@ process: { run_as_user: sandbox, run_as_group: sandbox }
         assert!(response.contains("\"format\":\"yaml\""), "{response}");
     }
 
+    #[tokio::test]
+    async fn mediated_connect_keeps_workload_bytes_read_with_the_synthesized_header() {
+        let Some(upstream_ip) = non_loopback_test_ipv4() else {
+            eprintln!("skipping: no routable non-loopback IPv4 test address");
+            return;
+        };
+        let upstream = TcpListener::bind((upstream_ip, 0)).await.unwrap();
+        let destination = upstream.local_addr().unwrap();
+        let (request_tx, request_rx) = tokio::sync::oneshot::channel();
+        tokio::spawn(async move {
+            let (mut stream, _) = upstream.accept().await.unwrap();
+            // Report whatever arrives before the request terminator or EOF, so a
+            // swallowed request shows up as an empty read, not as a hang.
+            let mut request = Vec::new();
+            loop {
+                let mut byte = [0_u8; 1];
+                match stream.read(&mut byte).await {
+                    Ok(1) => request.push(byte[0]),
+                    _ => break,
+                }
+                if request.ends_with(b"\r\n\r\n") {
+                    break;
+                }
+            }
+            request_tx.send(request).unwrap();
+            stream
+                .write_all(b"HTTP/1.1 204 No Content\r\nConnection: close\r\n\r\n")
+                .await
+                .unwrap();
+        });
+        let engine = Arc::new(
+            OpaEngine::from_strings(
+                include_str!("../data/sandbox-policy.rego"),
+                &format!(
+                    r#"
+network_policies:
+  allowed:
+    name: allowed
+    endpoints:
+      - host: "{upstream_ip}"
+        port: {port}
+        tls: skip
+    binaries:
+      - path: /usr/bin/curl
+"#,
+                    port = destination.port()
+                ),
+            )
+            .unwrap(),
+        );
+        let cache = Arc::new(BinaryIdentityCache::new());
+        let (stream, mut workload) = tokio::io::duplex(4096);
+        let (decision, completion) = tokio::sync::oneshot::channel();
+        let pending = PendingTcpOpen {
+            stream: Box::new(stream),
+            binary_identity: Ok(ContractBinaryIdentity {
+                executable: ContractExecutableIdentity {
+                    path: PathBuf::from("/usr/bin/curl"),
+                    digest: Some("44".repeat(32).parse().unwrap()),
+                },
+                ancestors: Vec::new(),
+                cmdline_paths: Vec::new(),
+            }),
+            destination,
+            socket: openshell_isolation_interface::contract::NetworkSocketMetadata {
+                socket_cookie: 7,
+                nonblocking: false,
+                process_generation: 1,
+            },
+            policy_generation: engine.current_generation(),
+            timing: MediationTiming::default(),
+            decision,
+        };
+        let (stream, supplied_identity, socket_addrs, transparent) =
+            preauthorize_transparent_open(pending, None, &engine, &cache, None, None, false, None)
+                .await
+                .expect("open is admitted");
+        assert_eq!(completion.await.unwrap(), TcpOpenDecision::RelayReady);
+        // The workload writes before the proxy reads anything, so its request sits
+        // right behind the synthesized CONNECT header in the proxy's first read.
+        workload
+            .write_all(
+                format!("GET /ping HTTP/1.1\r\nHost: {destination}\r\nConnection: close\r\n\r\n")
+                    .as_bytes(),
+            )
+            .await
+            .unwrap();
+        workload.shutdown().await.unwrap();
+        let handler = tokio::spawn(handle_mediated_connection(
+            tokio::io::BufReader::new(stream),
+            supplied_identity,
+            socket_addrs,
+            transparent,
+            None,
+            engine,
+            cache,
+            Arc::new(AtomicU32::new(0)),
+            None,
+            None,
+            AgentProposals::new(true),
+            Arc::new(None),
+            Arc::new(None),
+            Arc::new(None),
+            None,
+            None,
+            None,
+            None,
+            None,
+            None,
+        ));
+        let request = tokio::time::timeout(std::time::Duration::from_secs(5), request_rx)
+            .await
+            .expect("upstream never received the workload's request")
+            .unwrap();
+        assert!(
+            request.starts_with(b"GET /ping HTTP/1.1\r\n"),
+            "upstream received {:?} instead of the workload's request",
+            String::from_utf8_lossy(&request)
+        );
+        let mut response = Vec::new();
+        tokio::time::timeout(
+            std::time::Duration::from_secs(5),
+            workload.read_to_end(&mut response),
+        )
+        .await
+        .expect("response timed out")
+        .unwrap();
+        assert!(
+            response.starts_with(b"HTTP/1.1 204 "),
+            "{}",
+            String::from_utf8_lossy(&response)
+        );
+        tokio::time::timeout(std::time::Duration::from_secs(5), handler)
+            .await
+            .expect("handler did not finish")
+            .unwrap()
+            .unwrap();
+    }
+
     #[test]
     fn policy_local_route_requires_one_exact_host_and_an_origin_form_target() {
         assert!(valid_policy_local_request(