diff --git a/Cargo.lock b/Cargo.lock
index 5083fe5..9549099 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1652,7 +1652,7 @@ checksum = "09edd9e8b54e49e587e4f6295a7d29c3ea94d469cb40ab8ca70b288248a81db2"
 
 [[package]]
 name = "lesavka_client"
-version = "0.22.51"
+version = "0.22.52"
 dependencies = [
  "anyhow",
  "async-stream",
@@ -1686,7 +1686,7 @@ dependencies = [
 
 [[package]]
 name = "lesavka_common"
-version = "0.22.51"
+version = "0.22.52"
 dependencies = [
  "anyhow",
  "base64",
@@ -1698,7 +1698,7 @@ dependencies = [
 
 [[package]]
 name = "lesavka_server"
-version = "0.22.51"
+version = "0.22.52"
 dependencies = [
  "anyhow",
  "base64",
diff --git a/client/Cargo.toml b/client/Cargo.toml
index 4bcb078..e1f4e7b 100644
--- a/client/Cargo.toml
+++ b/client/Cargo.toml
@@ -4,7 +4,7 @@ path                    = "src/main.rs"
 
 [package]
 name                    = "lesavka_client"
-version                 = "0.22.51"
+version                 = "0.22.52"
 edition                 = "2024"
 
 [dependencies]
diff --git a/common/Cargo.toml b/common/Cargo.toml
index 70fd992..7e23786 100644
--- a/common/Cargo.toml
+++ b/common/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name                    = "lesavka_common"
-version                 = "0.22.51"
+version                 = "0.22.52"
 edition                 = "2024"
 build                   = "build.rs"
 
diff --git a/scripts/manual/run_synthetic_rct_uvc_probe.py b/scripts/manual/run_synthetic_rct_uvc_probe.py
index 1e0ca8b..59149cf 100755
--- a/scripts/manual/run_synthetic_rct_uvc_probe.py
+++ b/scripts/manual/run_synthetic_rct_uvc_probe.py
@@ -34,6 +34,7 @@ def parse_args() -> argparse.Namespace:
         )
     )
     parser.add_argument("--inject-host", default="", help="Theia SSH host, e.g. titan-jh")
+    parser.add_argument("--local-inject", action="store_true", help="run the synthetic injector directly on this host")
     parser.add_argument("--rct-host", default="", help="RCT SSH host, e.g. tethys")
     parser.add_argument("--server", default="https://127.0.0.1:50051")
     parser.add_argument("--inject-binary", default="/usr/local/bin/lesavka-synthetic-uplink")
@@ -124,8 +125,10 @@ def default_artifact_dir(mode: str) -> pathlib.Path:
 
 
 def run_remote_orchestrated(args: argparse.Namespace) -> int:
-    if not args.inject_host or not args.rct_host:
-        raise SystemExit("--inject-host and --rct-host are required unless --capture-only or --self-test is used")
+    if (not args.inject_host and not args.local_inject) or not args.rct_host:
+        raise SystemExit(
+            "--rct-host and either --inject-host or --local-inject are required unless --capture-only or --self-test is used"
+        )
     if not shutil.which("ssh") or not shutil.which("scp"):
         raise SystemExit("ssh and scp are required for the remote synthetic probe")
     width, height, fps = mode_dimensions(args)
@@ -227,6 +230,7 @@ def run_remote_orchestrated(args: argparse.Namespace) -> int:
                 "jpeg_quality": args.jpeg_quality,
                 "inject_max_frame_bytes": inject_max_frame_bytes,
                 "inject_host": args.inject_host,
+                "local_inject": args.local_inject,
                 "rct_host": args.rct_host,
             },
             indent=2,
@@ -239,6 +243,9 @@ def run_remote_orchestrated(args: argparse.Namespace) -> int:
         return subprocess.Popen(["ssh", args.rct_host, " ".join(shlex.quote(part) for part in capture_cmd)])
 
     def start_inject() -> subprocess.Popen[Any]:
+        if args.local_inject:
+            print(f"starting local synthetic uplink: {remote_inject_dir}", file=sys.stderr)
+            return subprocess.Popen(inject_cmd)
         print(f"starting synthetic uplink on {args.inject_host}: {remote_inject_dir}", file=sys.stderr)
         return subprocess.Popen(["ssh", args.inject_host, " ".join(shlex.quote(part) for part in inject_cmd)])
 
@@ -304,7 +311,13 @@ def run_remote_orchestrated(args: argparse.Namespace) -> int:
     local_inject = artifact_dir / "inject"
     if capture is not None:
         subprocess.run(["scp", "-r", f"{args.rct_host}:{remote_rct_dir}", str(local_capture)], check=False)
-    subprocess.run(["scp", "-r", f"{args.inject_host}:{remote_inject_dir}", str(local_inject)], check=False)
+    if args.local_inject:
+        if pathlib.Path(remote_inject_dir).exists():
+            if local_inject.exists():
+                shutil.rmtree(local_inject)
+            shutil.copytree(remote_inject_dir, local_inject)
+    else:
+        subprocess.run(["scp", "-r", f"{args.inject_host}:{remote_inject_dir}", str(local_inject)], check=False)
     capture_summary = local_capture / "summary.json"
     if capture_summary.exists():
         try:
@@ -334,12 +347,23 @@ def run_remote_orchestrated(args: argparse.Namespace) -> int:
         try:
             inject_data = json.loads(inject_summary.read_text())
             oversize_frames = int(inject_data.get("encoded_oversize_frames") or 0)
+            sent_frames = int(inject_data.get("sent_frames") or 0)
+            encoded_frames = int(inject_data.get("encoded_frames") or 0)
+            exit_reason = str(inject_data.get("exit_reason") or "")
             max_bytes = inject_data.get("encoded_max_bytes")
             max_frame_bytes = inject_data.get("max_frame_bytes")
             if oversize_frames:
                 diagnosis.append(
                     f"synthetic injector produced {oversize_frames} over-budget MJPEG frame(s), max={max_bytes} cap={max_frame_bytes}; the server will freeze instead of spooling those frames"
                 )
+            if inject_rc != 0 and "StreamWebcamMedia closed before accepting synthetic frame" in exit_reason:
+                diagnosis.append(
+                    f"synthetic injector was preempted after sending {sent_frames} frame(s); disconnect/pause the live Lesavka client upstream before running this isolated probe"
+                )
+            elif inject_rc != 0 and encoded_frames > 0 and not oversize_frames:
+                diagnosis.append(
+                    f"synthetic injector encoded {encoded_frames} in-budget frame(s) before failing; inspect inject/summary.json exit_reason for the stream-close cause"
+                )
         except Exception:
             pass
     summary = {
diff --git a/server/Cargo.toml b/server/Cargo.toml
index c64eb15..5e25276 100644
--- a/server/Cargo.toml
+++ b/server/Cargo.toml
@@ -16,7 +16,7 @@ bench                   = false
 
 [package]
 name                    = "lesavka_server"
-version                 = "0.22.51"
+version                 = "0.22.52"
 edition                 = "2024"
 autobins                = false
 
diff --git a/server/src/bin/lesavka-synthetic-uplink.rs b/server/src/bin/lesavka-synthetic-uplink.rs
index 7663edd..15c9671 100755
--- a/server/src/bin/lesavka-synthetic-uplink.rs
+++ b/server/src/bin/lesavka-synthetic-uplink.rs
@@ -130,6 +130,7 @@ struct MjpegEncoder {
 #[derive(Clone, Copy, Debug, Default)]
 struct EncodeStats {
     frames: u64,
+    sent_frames: u64,
     total_bytes: u128,
     min_bytes: usize,
     max_bytes: usize,
@@ -151,6 +152,10 @@ impl EncodeStats {
         }
     }
 
+    fn record_sent(&mut self) {
+        self.sent_frames = self.sent_frames.saturating_add(1);
+    }
+
     fn mean_bytes(&self) -> usize {
         if self.frames == 0 {
             0
@@ -352,7 +357,7 @@ async fn main() -> Result<()> {
             dir.join("command.txt"),
             std::env::args().collect::<Vec<_>>().join(" ") + "\n",
         )?;
-        write_summary(&args, None)?;
+        write_summary(&args, None, None)?;
     }
 
     let channel = connect_channel(&args).await?;
@@ -388,7 +393,11 @@ async fn main() -> Result<()> {
         let encoded = encoder.encode(sequence)?;
         encode_stats.record(encoded.len(), args.max_frame_bytes);
         if args.max_frame_bytes > 0 && encoded.len() > args.max_frame_bytes {
-            write_summary(&args, Some(&encode_stats))?;
+            write_summary(
+                &args,
+                Some(&encode_stats),
+                Some("encoded_frame_over_budget"),
+            )?;
             bail!(
                 "encoded synthetic frame {sequence} is {} bytes, above --max-frame-bytes {}; lower --jpeg-quality or use a more compressible synthetic pattern before trusting the RCT probe",
                 encoded.len(),
@@ -397,19 +406,28 @@ async fn main() -> Result<()> {
         }
         let bundle = synthetic_bundle(&args, sequence, pts_us, encoded);
         if tx.send(bundle).await.is_err() {
+            let closed_reason = format!(
+                "StreamWebcamMedia closed before accepting synthetic frame {sequence}; disconnect or pause any live Lesavka client upstream before running the isolated RCT probe"
+            );
             let response_result = response_task
                 .await
                 .context("joining StreamWebcamMedia task after early close")?;
             match response_result {
-                Ok(()) => bail!(
-                    "StreamWebcamMedia closed before accepting synthetic frame {sequence}; disconnect or pause any live Lesavka client upstream before running the isolated RCT probe"
-                ),
+                Ok(()) => {
+                    write_summary(&args, Some(&encode_stats), Some(&closed_reason))?;
+                    bail!("{closed_reason}");
+                }
                 Err(err) => {
+                    let error_reason = format!(
+                        "StreamWebcamMedia closed before accepting synthetic frame {sequence}: {err:#}"
+                    );
+                    write_summary(&args, Some(&encode_stats), Some(&error_reason))?;
                     return Err(err)
                         .context("StreamWebcamMedia closed before accepting synthetic frame");
                 }
             }
         }
+        encode_stats.record_sent();
         if args.print_every > 0 && sequence > 0 && sequence % args.print_every == 0 {
             eprintln!("sent synthetic frame {sequence}/{total_frames}");
         }
@@ -418,7 +436,7 @@ async fn main() -> Result<()> {
     response_task
         .await
         .context("joining StreamWebcamMedia task")??;
-    write_summary(&args, Some(&encode_stats))?;
+    write_summary(&args, Some(&encode_stats), Some("complete"))?;
     eprintln!("lesavka synthetic uplink complete: frames={total_frames}");
     Ok(())
 }
@@ -642,11 +660,15 @@ fn unix_millis() -> u64 {
         .min(u128::from(u64::MAX)) as u64
 }
 
-fn write_summary(args: &Args, stats: Option<&EncodeStats>) -> Result<()> {
+fn write_summary(
+    args: &Args,
+    stats: Option<&EncodeStats>,
+    exit_reason: Option<&str>,
+) -> Result<()> {
     if let Some(dir) = &args.artifact_dir {
         std::fs::write(
             dir.join("summary.json"),
-            args_summary_json(args, stats) + "\n",
+            args_summary_json(args, stats, exit_reason) + "\n",
         )?;
     }
     Ok(())
@@ -658,8 +680,19 @@ fn json_usize_or_null(value: Option<usize>) -> String {
         .unwrap_or_else(|| "null".to_string())
 }
 
-fn args_summary_json(args: &Args, stats: Option<&EncodeStats>) -> String {
+fn json_string_or_null(value: Option<&str>) -> String {
+    value
+        .map(|value| format!("{value:?}"))
+        .unwrap_or_else(|| "null".to_string())
+}
+
+fn args_summary_json(
+    args: &Args,
+    stats: Option<&EncodeStats>,
+    exit_reason: Option<&str>,
+) -> String {
     let frames = stats.map(|stats| stats.frames).unwrap_or(0);
+    let sent_frames = stats.map(|stats| stats.sent_frames).unwrap_or(0);
     let min_bytes =
         json_usize_or_null(stats.and_then(|stats| (stats.frames > 0).then_some(stats.min_bytes)));
     let max_bytes =
@@ -668,8 +701,9 @@ fn args_summary_json(args: &Args, stats: Option<&EncodeStats>) -> String {
         stats.and_then(|stats| (stats.frames > 0).then_some(stats.mean_bytes())),
     );
     let oversize_frames = stats.map(|stats| stats.oversize_frames).unwrap_or(0);
+    let exit_reason = json_string_or_null(exit_reason);
     format!(
-        "{{\"schema\":\"lesavka.synthetic-uplink.v1\",\"server\":{server:?},\"width\":{width},\"height\":{height},\"fps\":{fps},\"duration_s\":{duration:.3},\"session_id\":{session},\"tls\":{tls},\"jpeg_quality\":{quality},\"max_frame_bytes\":{max_frame_bytes},\"encoded_frames\":{frames},\"encoded_min_bytes\":{min_bytes},\"encoded_max_bytes\":{max_bytes},\"encoded_mean_bytes\":{mean_bytes},\"encoded_oversize_frames\":{oversize_frames}}}",
+        "{{\"schema\":\"lesavka.synthetic-uplink.v1\",\"server\":{server:?},\"width\":{width},\"height\":{height},\"fps\":{fps},\"duration_s\":{duration:.3},\"session_id\":{session},\"tls\":{tls},\"jpeg_quality\":{quality},\"max_frame_bytes\":{max_frame_bytes},\"encoded_frames\":{frames},\"sent_frames\":{sent_frames},\"encoded_min_bytes\":{min_bytes},\"encoded_max_bytes\":{max_bytes},\"encoded_mean_bytes\":{mean_bytes},\"encoded_oversize_frames\":{oversize_frames},\"exit_reason\":{exit_reason}}}",
         server = args.server,
         width = args.width,
         height = args.height,
@@ -680,10 +714,12 @@ fn args_summary_json(args: &Args, stats: Option<&EncodeStats>) -> String {
         quality = args.jpeg_quality,
         max_frame_bytes = args.max_frame_bytes,
         frames = frames,
+        sent_frames = sent_frames,
         min_bytes = min_bytes,
         max_bytes = max_bytes,
         mean_bytes = mean_bytes,
         oversize_frames = oversize_frames,
+        exit_reason = exit_reason,
     )
 }
 
diff --git a/tests/manual/server/rct/synthetic_rct_uvc_probe_manual_contract.rs b/tests/manual/server/rct/synthetic_rct_uvc_probe_manual_contract.rs
index ff62034..8c95e49 100644
--- a/tests/manual/server/rct/synthetic_rct_uvc_probe_manual_contract.rs
+++ b/tests/manual/server/rct/synthetic_rct_uvc_probe_manual_contract.rs
@@ -35,6 +35,7 @@ fn synthetic_probe_keeps_bundled_network_ingress_and_rct_comparison_markers() {
         "lesavka-synthetic-uplink",
         "https://127.0.0.1:50051",
         "--inject-host",
+        "--local-inject",
         "--rct-host",
         "--capture-only",
         "--capture-before-inject",
@@ -57,8 +58,11 @@ fn synthetic_probe_keeps_bundled_network_ingress_and_rct_comparison_markers() {
         "decoded_pct",
         "diagnosis",
         "encoded_oversize_frames",
+        "sent_frames",
+        "exit_reason",
         "decoded_sequence_counts",
         "synthetic uplink completed but RCT capture did not finish",
+        "synthetic injector was preempted after sending",
         "synthetic uplink exited before capture warmup completed",
         "max_lower_mae",
         "ffmpeg",