diff --git a/README.md b/README.md
index ae83ea0..dde45a0 100644
--- a/README.md
+++ b/README.md
@@ -1,13 +1,16 @@
 # iperf3-gui
 
-A Flutter-based Android GUI wrapper for iperf3, the popular network performance measurement tool.
+A Flutter-based Android GUI wrapper for iperf3, the popular network performance
+measurement tool.
 
 ## Features
 
 - Client-mode network throughput testing
-- Simple UI: enter server address, port, and press GO
-- Raw iperf3 output display
-- Bundled iperf3 v3.21 binaries for arm64-v8a and armeabi-v7a
+- Configurable server, port, duration and parallel streams
+- Live iperf3 output, streamed line by line while the test runs
+- Stop a running test early
+- Copy the transcript to the clipboard
+- iperf3 3.19 compiled into the app as a native library — no external binary
 
 ## Architecture
 
@@ -15,33 +18,62 @@ A Flutter-based Android GUI wrapper for iperf3, the popular network performance
 lib/
 ├── domain/
 │   ├── models/          # TestConfiguration, Iperf3Result
-│   └── services/        # Iperf3Service (Process runner)
+├── data/
+│   └── services/        # Iperf3Service (MethodChannel → JNI)
 ├── ui/
 │   └── features/
 │       └── test_run/    # TestRunScreen, TestRunViewModel
-├── main.dart            # App entry point
-└── pubspec.yaml         # Dependencies: provider, path_provider
+└── main.dart            # App entry point
+
+android/app/src/main/
+├── kotlin/…/IperfRunner.kt   # MethodChannel handler, runs tests off the platform thread
+└── cpp/iperf_jni.c           # JNI bridge into the iperf3 API
 ```
 
+See [docs/README.md](docs/README.md) for the data flow, the native API surface
+and the design decisions behind them.
+
+## Why JNI instead of executing a binary
+
+Android SELinux in Enforcing mode blocks `execve()` from the `untrusted_app`
+domain, so shipping an iperf3 ELF in assets and running it via `Process.start()`
+fails with "Permission denied". iperf3 is therefore compiled as a shared library
+(`libiperf3jni.so`) and called in-process over JNI.
+
+`assets/iperf3/` still holds the pre-compiled binaries from that earlier
+approach. They are not declared in `pubspec.yaml`, so they are not packaged into
+the APK, and nothing in the app reads them.
+
 ## Building
 
 Prerequisites:
-- Flutter 3.47+ 
+- Flutter 3.47+
 - Android SDK with platform android-36
 - JDK 17
+- NDK r28+ and CMake 3.22.1 (for the native build)
 
 ```bash
-flutter create . --org novoyuuparosk --project-name iperf3gui
 flutter pub get
 flutter analyze
+flutter test
 flutter build apk --debug
+adb install -r build/app/outputs/flutter-apk/app-debug.apk
 ```
 
-### iperf3 Binaries
+## Testing against a local server
 
-Pre-compiled binaries are sourced from [davidBar-On/android-iperf3](https://github.com/davidBar-On/android-iperf3)
-and bundled in `assets/iperf3/` (arm64-v8a and armeabi-v7a for Android 28+).
+```bash
+iperf3 -s -p 5201                 # on a machine on the same network
+ip -4 addr show                   # note its address
+```
+
+Enter that address in the app, then press GO.
+
+## Dependencies
+
+- Dart: `provider`
+- Native: iperf3 3.19 + cJSON, built by CMake for `armeabi-v7a` and `arm64-v8a`
 
 ## License
 
-MIT — bundled iperf3 v3.21 is BSD-3-Clause licensed.
+MIT — bundled iperf3 3.19 is BSD-3-Clause licensed.
diff --git a/android/app/src/main/cpp/iperf_jni.c b/android/app/src/main/cpp/iperf_jni.c
index a8f874b..5b4cfac 100644
--- a/android/app/src/main/cpp/iperf_jni.c
+++ b/android/app/src/main/cpp/iperf_jni.c
@@ -5,12 +5,25 @@
  * the Flutter app to run iperf3 tests natively inside the app process
  * (no Process.start needed, no SELinux restrictions).
  *
+ * THREADING NOTE:
+ * runIperfLive() BLOCKS for the whole duration of the test. Kotlin must
+ * call it from a worker thread, never from the Flutter platform thread.
+ *
+ * PIPE / SHUTDOWN NOTE:
+ * iperf's output goes to a pipe drained by a reader thread that blocks in
+ * fgets(). The reader only sees EOF once the write end is closed, so the
+ * write end MUST be closed before pthread_join() — joining first deadlocks.
+ * The state struct is owned solely by the JNI caller, which frees it after
+ * joining the reader; the reader must never free it.
+ *
  * SIGNAL HANDLING NOTE:
  * iperf3's run() function (called from iperf_run_client()) uses
  * setjmp/longjmp for graceful signal handling. The JNI bridge must
  * replicate this setup — otherwise iperf_catch_sigend() installs
  * handlers that longjmp to an unset buffer, causing undefined
- * behaviour (typically a SIGSEGV or hang).
+ * behaviour (typically a SIGSEGV or hang). Handlers are restored to
+ * SIG_DFL once the test finishes so a later signal cannot longjmp into
+ * a stack frame that no longer exists.
  */
 
 #include <stdio.h>
@@ -23,6 +36,7 @@
 #include <android/log.h>
 #include <jni.h>
 #include <pthread.h>
+#include <sys/socket.h>
 
 #include "iperf.h"
 #include "iperf_api.h"
@@ -33,31 +47,39 @@
 #define LOGI(...) __android_log_print(ANDROID_LOG_INFO, TAG, __VA_ARGS__)
 #define LOGE(...) __android_log_print(ANDROID_LOG_ERROR, TAG, __VA_ARGS__)
 
-/* Global state for controlling the iperf test */
+/* ------------------------------------------------------------------ */
+/* Global state for controlling the iperf test.                        */
+/*                                                                     */
+/* g_test is written by the worker thread running the test and read by  */
+/* the platform thread in forceStopIperfTest()/isTestRunning(), so all  */
+/* access is serialised through g_test_mutex. The mutex is never held   */
+/* across iperf_run_client() — only around pointer publish/retire and   */
+/* the (short) stop request.                                           */
+/* ------------------------------------------------------------------ */
 static struct iperf_test *g_test = NULL;
+static pthread_mutex_t g_test_mutex = PTHREAD_MUTEX_INITIALIZER;
 static volatile int g_stop = 0;
 static char g_tmp_template[1024] = "/data/local/tmp/iperf3.XXXXXX";
 
-/* Per-call state to pass between JNI and the reader thread.
+/* Per-call state shared between the JNI caller and the reader thread.
  * We store the callback object (global ref) and method IDs.
  * Callbacks are invoked via CallVoidMethod, NOT as function pointers. */
 struct iperf_run_state {
-    JNIEnv *env;
     jobject callback_ref;       /* Global ref to the callback object */
     jmethodID mid_output;       /* Method ID for onOutput(String) */
     jmethodID mid_error;        /* Method ID for onError(String) */
     jmethodID mid_complete;     /* Method ID for onComplete() */
-    FILE *outfile;
+    FILE *outfile;              /* Pipe write end; NULL once closed */
     int pipe_fd[2];
     JavaVM *jvm;
     pthread_t reader_thread;
+    int reader_started;         /* Only join if pthread_create succeeded */
 };
 
 /* Helper: invoke the output callback via CallVoidMethod */
-static void signal_output(struct iperf_run_state *state, const char *msg) {
-    if (!state || !msg || !msg[0]) return;
-    JNIEnv *env = state->env;
-    if (!env || !state->mid_output) return;
+static void signal_output(JNIEnv *env, struct iperf_run_state *state,
+                          const char *msg) {
+    if (!env || !state || !msg || !msg[0] || !state->mid_output) return;
 
     jstring jline = (*env)->NewStringUTF(env, msg);
     if (jline) {
@@ -67,10 +89,9 @@ static void signal_output(struct iperf_run_state *state, const char *msg) {
 }
 
 /* Helper: invoke the error callback via CallVoidMethod */
-static void signal_error(struct iperf_run_state *state, const char *msg) {
-    if (!state || !msg) return;
-    JNIEnv *env = state->env;
-    if (!env || !state->mid_error) return;
+static void signal_error(JNIEnv *env, struct iperf_run_state *state,
+                         const char *msg) {
+    if (!env || !state || !msg || !state->mid_error) return;
 
     jstring jmsg = (*env)->NewStringUTF(env, msg);
     if (jmsg) {
@@ -80,10 +101,8 @@ static void signal_error(struct iperf_run_state *state, const char *msg) {
 }
 
 /* Helper: invoke the complete callback via CallVoidMethod */
-static void signal_complete(struct iperf_run_state *state) {
-    if (!state || !state->mid_complete) return;
-    JNIEnv *env = state->env;
-    if (!env) return;
+static void signal_complete(JNIEnv *env, struct iperf_run_state *state) {
+    if (!env || !state || !state->mid_complete) return;
 
     (*env)->CallVoidMethod(env, state->callback_ref, state->mid_complete);
 }
@@ -91,6 +110,9 @@ static void signal_complete(struct iperf_run_state *state) {
 /* ------------------------------------------------------------------ */
 /* Output reader thread — reads from iperf's output pipe and forwards */
 /* each line to the Java callback via JNI.                            */
+/*                                                                    */
+/* Exits when the write end of the pipe is closed (EOF). Does NOT own */
+/* `state`: the JNI caller frees it after joining this thread.        */
 /* ------------------------------------------------------------------ */
 static void *reader_thread_func(void *arg) {
     struct iperf_run_state *state = (struct iperf_run_state *) arg;
@@ -101,6 +123,10 @@ static void *reader_thread_func(void *arg) {
     ret = (*state->jvm)->AttachCurrentThread(state->jvm, &env, NULL);
     if (ret != JNI_OK) {
         LOGE("AttachCurrentThread failed: %d", ret);
+        /* Still drain the pipe so writers never block on a full pipe. */
+        char drain[1024];
+        while (read(state->pipe_fd[0], drain, sizeof(drain)) > 0) { }
+        close(state->pipe_fd[0]);
         return NULL;
     }
 
@@ -118,49 +144,52 @@ static void *reader_thread_func(void *arg) {
                 (*env)->DeleteLocalRef(env, line);
             }
         }
-        fclose(fp);
+        fclose(fp); /* also closes pipe_fd[0] */
+    } else {
+        close(state->pipe_fd[0]);
     }
 
     /* Detach this native thread */
     (*state->jvm)->DetachCurrentThread(state->jvm);
-
-    /* Free the state struct — caller owns it */
-    free(state);
     return NULL;
 }
 
 /* ------------------------------------------------------------------ */
-/* Convert a Java String[] into a native char** argv array.           */
+/* Build a native argv from a Java String[], prepending "iperf3".      */
+/*                                                                    */
+/* iperf_parse_arguments() expects argv[0] to be the program name;     */
+/* passing the Dart args directly would make argv[0] "-c", which       */
+/* iperf3 misreads as the program name rather than the client flag.    */
 /* ------------------------------------------------------------------ */
-static char **java_string_array_to_argv(JNIEnv *env, jobjectArray str_array,
-                                        int *out_argc) {
-    int argc = (*env)->GetArrayLength(env, str_array);
-    if (argc <= 0) {
+static char **build_argv(JNIEnv *env, jobjectArray str_array, int *out_argc) {
+    int user_argc = (*env)->GetArrayLength(env, str_array);
+    if (user_argc < 0) user_argc = 0;
+
+    int argc = user_argc + 1; /* +1 for argv[0] */
+    char **argv = malloc((argc + 1) * sizeof(char *));
+    if (!argv) {
         *out_argc = 0;
         return NULL;
     }
 
-    char **argv = malloc((argc + 1) * sizeof(char *));
-    if (!argv) return NULL;
-
-    for (int i = 0; i < argc; i++) {
-        jstring jstr = (jstring) (*env)->GetObjectArrayElement(env,
-                                                                str_array, i);
-        const char *cstr = (*env)->GetStringUTFChars(env, jstr, NULL);
+    argv[0] = strdup("iperf3");
+    for (int i = 0; i < user_argc; i++) {
+        jstring jstr = (jstring) (*env)->GetObjectArrayElement(env, str_array, i);
+        const char *cstr = jstr ? (*env)->GetStringUTFChars(env, jstr, NULL) : NULL;
         if (cstr) {
-            argv[i] = strdup(cstr);
+            argv[i + 1] = strdup(cstr);
             (*env)->ReleaseStringUTFChars(env, jstr, cstr);
         } else {
-            argv[i] = strdup("");
+            argv[i + 1] = strdup("");
         }
-        (*env)->DeleteLocalRef(env, jstr);
+        if (jstr) (*env)->DeleteLocalRef(env, jstr);
     }
     argv[argc] = NULL; /* NULL-terminated for iperf */
     *out_argc = argc;
     return argv;
 }
 
-/* Free an argv array returned by java_string_array_to_argv() */
+/* Free an argv array returned by build_argv() */
 static void free_argv(char **argv, int argc) {
     if (!argv) return;
     for (int i = 0; i < argc; i++) {
@@ -170,42 +199,79 @@ static void free_argv(char **argv, int argc) {
 }
 
 /* ------------------------------------------------------------------ */
-/* Internal: clean up after iperf_run_client returns (normal path).   */
-/* Must be called only on the normal return path (NOT after longjmp). */
+/* Close the pipe write end. Idempotent — both the normal and the      */
+/* longjmp path call it, and the second call must be a no-op.          */
+/*                                                                    */
+/* Closing this is what makes the reader thread see EOF and exit, so   */
+/* it must happen before any pthread_join().                           */
+/* ------------------------------------------------------------------ */
+static void close_outfile(struct iperf_run_state *state) {
+    if (state && state->outfile) {
+        fflush(state->outfile);
+        fclose(state->outfile);
+        state->outfile = NULL;
+    }
+}
+
+/* Retire the global test pointer and free it, under the mutex. */
+static void retire_test(void) {
+    pthread_mutex_lock(&g_test_mutex);
+    struct iperf_test *test = g_test;
+    g_test = NULL;
+    if (test) {
+        /* outfile is a closed FILE* by now — point it somewhere harmless so
+         * nothing in the teardown path can write to a dead stream. */
+        test->outfile = stdout;
+        iperf_free_test(test);
+    }
+    pthread_mutex_unlock(&g_test_mutex);
+}
+
+/* ------------------------------------------------------------------ */
+/* Internal: clean up after iperf_run_client returns and report the    */
+/* outcome to Java. Called from both the normal and the longjmp path.  */
+/* Frees `state`; do not touch it afterwards.                          */
 /* ------------------------------------------------------------------ */
 static void iperf_cleanup_and_signal(JNIEnv *env,
                                      struct iperf_run_state *state,
                                      char **argv, int argc,
                                      int ret, int stopped) {
-    /* Wait for reader thread to finish */
-    pthread_join(state->reader_thread, NULL);
+    /* Close the write end FIRST: the reader thread is blocked in fgets()
+     * and only unblocks on EOF. Joining before this would deadlock. */
+    close_outfile(state);
 
-    /* Flush and close output */
-    fflush(state->outfile);
-    fclose(state->outfile);
+    if (state->reader_started) {
+        pthread_join(state->reader_thread, NULL);
+        state->reader_started = 0;
+    }
 
-    /* Clean up iperf */
-    iperf_free_test(g_test);
-    g_test = NULL;
+    /* Restore default signal handlers before g_sigend_jmp_buf goes stale. */
+    iperf_catch_sigend(SIG_DFL);
 
-    /* Free argv */
+    retire_test();
     free_argv(argv, argc);
 
+    /* A user-requested stop shuts down the control socket, so
+     * iperf_run_client() returns -1 with "Broken pipe" — expected, not a
+     * failure. Check g_stop so that path is reported as a stop, not an error. */
+    int user_stopped = stopped || g_stop;
+    g_stop = 0;
+
     /* Signal result to Java */
-    if (stopped) {
-        signal_output(state, "[iPerf JNI] Test was stopped by user.\n");
+    if (user_stopped) {
+        signal_output(env, state, "[iPerf JNI] Test was stopped by user.\n");
     } else if (ret < 0) {
         char errbuf[256];
         snprintf(errbuf, sizeof(errbuf),
                  "[iPerf JNI] Test failed: %s\n",
                  iperf_strerror(i_errno));
-        signal_error(state, errbuf);
+        signal_error(env, state, errbuf);
     } else {
-        signal_output(state, "[iPerf JNI] Test completed successfully.\n");
+        signal_output(env, state, "[iPerf JNI] Test completed successfully.\n");
     }
 
     /* Signal completion to Java */
-    signal_complete(state);
+    signal_complete(env, state);
 
     /* Free global ref and state struct */
     (*env)->DeleteGlobalRef(env, state->callback_ref);
@@ -228,80 +294,93 @@ static void sigend_handler(int sig) {
 /* ------------------------------------------------------------------ */
 /* JNI: Start an iperf3 test with the given arguments.                */
 /* Signature: void runIperfLive(String[] args, IperfCallback cb)      */
+/*                                                                    */
+/* BLOCKS until the test finishes — call from a worker thread.         */
 /* ------------------------------------------------------------------ */
 JNIEXPORT void JNICALL
 Java_com_novoyuuparosk_iperf3gui_IperfRunner_runIperfLive(
         JNIEnv *env, jobject thiz,
         jobjectArray arguments, jobject callback) {
 
+    /* Resolve callback method IDs up front so failures can be reported. */
+    jclass callback_cls = (*env)->GetObjectClass(env, callback);
+    jmethodID mid_output = (*env)->GetMethodID(
+            env, callback_cls, "onOutput", "(Ljava/lang/String;)V");
+    jmethodID mid_error = (*env)->GetMethodID(
+            env, callback_cls, "onError", "(Ljava/lang/String;)V");
+    jmethodID mid_complete = (*env)->GetMethodID(
+            env, callback_cls, "onComplete", "()V");
+
+    /* Report a startup failure directly on the callback object and finish,
+     * so Dart's completer always resolves instead of waiting for a timeout. */
+    #define FAIL_EARLY(msg) do {                                              \
+        LOGE("%s", msg);                                                      \
+        if (mid_error) {                                                      \
+            jstring jm = (*env)->NewStringUTF(env, msg);                      \
+            if (jm) {                                                         \
+                (*env)->CallVoidMethod(env, callback, mid_error, jm);         \
+                (*env)->DeleteLocalRef(env, jm);                              \
+            }                                                                 \
+        }                                                                     \
+        if (mid_complete) (*env)->CallVoidMethod(env, callback, mid_complete); \
+    } while (0)
+
+    /* Refuse to start a second concurrent test — the globals below hold
+     * exactly one test's worth of state. */
+    pthread_mutex_lock(&g_test_mutex);
+    int busy = (g_test != NULL);
+    pthread_mutex_unlock(&g_test_mutex);
+    if (busy) {
+        FAIL_EARLY("[iPerf JNI] A test is already running.");
+        return;
+    }
+
     /* Create the iperf test object */
     struct iperf_test *test = iperf_new_test();
     if (!test) {
-        const char *err = "Failed to create iperf test";
-        LOGE("%s", err);
+        FAIL_EARLY("[iPerf JNI] Failed to create iperf test");
         return;
     }
 
     iperf_defaults(test);
-    g_test = test;
 
-    /*
-     * Convert Java String[] -> char** argv, prepending "iperf3" as argv[0].
-     * iperf_parse_arguments() expects argv[0] to be the program name;
-     * passing args directly from Dart means argv[0] would be "-c",
-     * which iperf3 misinterprets as the program name, not the client flag.
-     */
-    int dart_argc = (*env)->GetArrayLength(env, arguments);
-    int total_argc = dart_argc + 1;  /* +1 for "iperf3" */
-    char **argv = malloc((total_argc + 1) * sizeof(char *));
+    pthread_mutex_lock(&g_test_mutex);
+    g_test = test;
+    pthread_mutex_unlock(&g_test_mutex);
+
+    int total_argc = 0;
+    char **argv = build_argv(env, arguments, &total_argc);
     if (!argv) {
-        const char *err = "Failed to allocate argv";
-        LOGE("%s", err);
-        iperf_free_test(test);
-        g_test = NULL;
+        retire_test();
+        FAIL_EARLY("[iPerf JNI] Failed to allocate argv");
         return;
     }
-    argv[0] = strdup("iperf3");
-    for (int i = 0; i < dart_argc; i++) {
-        jstring jstr = (jstring) (*env)->GetObjectArrayElement(env, arguments, i);
-        const char *cstr = (*env)->GetStringUTFChars(env, jstr, NULL);
-        if (cstr) {
-            argv[i + 1] = strdup(cstr);
-            (*env)->ReleaseStringUTFChars(env, jstr, cstr);
-        } else {
-            argv[i + 1] = strdup("");
-        }
-        (*env)->DeleteLocalRef(env, jstr);
-    }
-    argv[total_argc] = NULL; /* NULL-terminated for iperf */
 
-    /* Set a reasonable connect timeout (30s) to avoid hanging on DNS resolution.
-     * Default iperf3 connect timeout is 120s which is far too long. */
+    /* Set a reasonable connect timeout (30s) to avoid hanging on DNS
+     * resolution. Default iperf3 connect timeout is 120s, far too long for a
+     * phone UI. Set before parsing so an explicit --connect-timeout wins. */
     test->settings->connect_timeout = 30000;
 
     /* Parse arguments */
     if (iperf_parse_arguments(test, total_argc, argv) < 0) {
         char errbuf[256];
         snprintf(errbuf, sizeof(errbuf),
-                 "Argument parse error: %s", iperf_strerror(i_errno));
-        LOGE("Parse error: %s", errbuf);
+                 "[iPerf JNI] Argument parse error: %s", iperf_strerror(i_errno));
         free_argv(argv, total_argc);
-        iperf_free_test(test);
-        g_test = NULL;
+        retire_test();
+        FAIL_EARLY(errbuf);
         return;
     }
 
-    /* Create a pipe to capture iperf's stdout/stderr */
+    /* Create a pipe to capture iperf's output */
     int pipefd[2];
     if (pipe(pipefd) != 0) {
+        char errbuf[256];
+        snprintf(errbuf, sizeof(errbuf),
+                 "[iPerf JNI] Failed to create output pipe: %s", strerror(errno));
         free_argv(argv, total_argc);
-        const char *err = "Failed to create output pipe";
-        LOGE("pipe() failed: %s", strerror(errno));
-
-        signal_error((struct iperf_run_state *) 0, err);
-
-        iperf_free_test(test);
-        g_test = NULL;
+        retire_test();
+        FAIL_EARLY(errbuf);
         return;
     }
 
@@ -312,28 +391,33 @@ Java_com_novoyuuparosk_iperf3gui_IperfRunner_runIperfLive(
         free_argv(argv, total_argc);
         close(pipefd[0]);
         close(pipefd[1]);
-        iperf_free_test(test);
-        g_test = NULL;
+        retire_test();
+        FAIL_EARLY("[iPerf JNI] Failed to allocate run state");
         return;
     }
 
-    /* Resolve callback method IDs (do this in the calling thread) */
-    jclass callback_cls = (*env)->GetObjectClass(env, callback);
-    state->mid_output = (*env)->GetMethodID(
-            env, callback_cls, "onOutput", "(Ljava/lang/String;)V");
-    state->mid_error = (*env)->GetMethodID(
-            env, callback_cls, "onError", "(Ljava/lang/String;)V");
-    state->mid_complete = (*env)->GetMethodID(
-            env, callback_cls, "onComplete", "()V");
+    FILE *outfile = fdopen(pipefd[1], "w");
+    if (!outfile) {
+        free(state);
+        free_argv(argv, total_argc);
+        close(pipefd[0]);
+        close(pipefd[1]);
+        retire_test();
+        FAIL_EARLY("[iPerf JNI] Failed to open output stream");
+        return;
+    }
 
-    /* Get JavaVM for thread attachment */
+    /* Get JavaVM for reader-thread attachment */
     JavaVM *jvm;
     (*env)->GetJavaVM(env, &jvm);
 
-    state->env = env;
+    state->mid_output = mid_output;
+    state->mid_error = mid_error;
+    state->mid_complete = mid_complete;
     state->callback_ref = (*env)->NewGlobalRef(env, callback);
-    state->outfile = fdopen(pipefd[1], "w");
+    state->outfile = outfile;
     state->pipe_fd[0] = pipefd[0];
+    state->pipe_fd[1] = pipefd[1];
     state->jvm = jvm;
 
     /* Redirect iperf's output to our pipe */
@@ -346,42 +430,44 @@ Java_com_novoyuuparosk_iperf3gui_IperfRunner_runIperfLive(
      * the strdup internally. */
     iperf_set_test_template(test, g_tmp_template);
 
+    /* Spawn reader thread to forward iperf output to Java. Started before
+     * the test so early output is not lost, and before setjmp so the
+     * longjmp path can rely on reader_started being accurate. */
+    if (pthread_create(&state->reader_thread, NULL,
+                       reader_thread_func, state) != 0) {
+        close_outfile(state);
+        close(pipefd[0]);
+        free_argv(argv, total_argc);
+        retire_test();
+        (*env)->DeleteGlobalRef(env, state->callback_ref);
+        free(state);
+        FAIL_EARLY("[iPerf JNI] Failed to start output reader thread");
+        return;
+    }
+    state->reader_started = 1;
+
+    #undef FAIL_EARLY
+
     /*
      * Set up signal handling BEFORE calling iperf_run_client().
      * iperf3's run() function uses setjmp/longjmp for signal handling.
      * - setjmp returns 0 on first call (normal path)
      * - setjmp returns non-zero when called via longjmp (signal path)
      *
-     * Both paths share the same `state`, `argv`, `argc` variables,
-     * so the stack frame is preserved across the longjmp.
+     * `state` and `argv` are assigned before setjmp and never reassigned
+     * afterwards, so both paths observe the same values.
      */
     if (setjmp(g_sigend_jmp_buf) == 0) {
         /* Normal path — run the test */
         signal(SIGPIPE, SIG_IGN);  /* Ignore SIGPIPE for socket errors */
         iperf_catch_sigend(sigend_handler);
 
-        /* Notify Java that the test is starting */
-        signal_output(state, "[iPerf JNI] Starting iPerf3 client...\n");
+        signal_output(env, state, "[iPerf JNI] Starting iPerf3 client...\n");
 
-        /* Spawn reader thread to forward iperf output to Java */
-        if (pthread_create(&state->reader_thread, NULL,
-                           reader_thread_func, state) != 0) {
-            free_argv(argv, total_argc);
-            close(pipefd[0]);
-            close(pipefd[1]);
-            const char *err = "Failed to start output reader thread";
-            LOGE("%s", err);
-            signal_error(state, err);
-            iperf_free_test(test);
-            g_test = NULL;
-            free(state);
-            return;
-        }
-
-        /* Run the test */
         g_stop = 0;
         int ret = iperf_run_client(test);
-        LOGI("iperf_run_client returned: %d i_errno=%d strerror=%s ctrl_sck=%d", ret, i_errno, iperf_strerror(i_errno), test->ctrl_sck);
+        LOGI("iperf_run_client returned: %d i_errno=%d strerror=%s",
+             ret, i_errno, iperf_strerror(i_errno));
 
         /*
          * We get here after iperf_run_client returns normally.
@@ -392,47 +478,43 @@ Java_com_novoyuuparosk_iperf3gui_IperfRunner_runIperfLive(
     } else {
         /*
          * We got here via longjmp() from sigend_handler.
-         * Clean up resources allocated before the setjmp.
-         * NOTE: state, argv, argc are still valid on the stack.
+         * iperf_cleanup_and_signal() closes the pipe, joins the reader and
+         * frees everything, so there is nothing to unwind by hand here.
          */
         LOGI("Test interrupted by signal %d", g_signed_sig);
-
-        /* Stop flag for cleanup */
         g_stop = 1;
-
-        /* Close the output file (the pipe write end) */
-        if (state->outfile) {
-            fclose(state->outfile);
-        }
-
-        /* Free argv (argv is still valid across longjmp since it's on stack) */
-        free_argv(argv, total_argc);
-
-        /* Run the cleanup with stopped=true.
-         * Note: argv is NULL, argc=0 so free_argv is a no-op.
-         * The state struct will be freed inside this function. */
-        iperf_cleanup_and_signal(env, state, NULL, 0, 0, 1);
+        iperf_cleanup_and_signal(env, state, argv, total_argc, 0, 1);
     }
 }
 
 /* ------------------------------------------------------------------ */
 /* JNI: Gracefully stop a running iperf3 test.                        */
 /* Signature: void forceStopIperfTest(IperfCallback cb)               */
+/*                                                                    */
+/* Runs on the platform thread while the test runs on a worker thread, */
+/* so the whole body holds g_test_mutex: that keeps the worker from    */
+/* freeing g_test underneath us.                                      */
 /* ------------------------------------------------------------------ */
 JNIEXPORT void JNICALL
 Java_com_novoyuuparosk_iperf3gui_IperfRunner_forceStopIperfTest(
         JNIEnv *env, jobject thiz, jobject callback) {
-    if (!g_test || g_test->done) return;
 
-    /* Set the stop flag */
-    g_stop = 1;
-    g_test->done = 1;
-    iperf_set_send_state(g_test, IPERF_DONE);
+    pthread_mutex_lock(&g_test_mutex);
+    int requested = 0;
+    if (g_test && !g_test->done) {
+        g_stop = 1;
+        g_test->done = 1;
+        iperf_set_send_state(g_test, IPERF_DONE);
 
-    /* Try to unblock select() on the control socket */
-    if (g_test->ctrl_sck >= 0) {
-        shutdown(g_test->ctrl_sck, SHUT_RDWR);
+        /* Try to unblock select() on the control socket */
+        if (g_test->ctrl_sck >= 0) {
+            shutdown(g_test->ctrl_sck, SHUT_RDWR);
+        }
+        requested = 1;
     }
+    pthread_mutex_unlock(&g_test_mutex);
+
+    if (!requested) return;
 
     /* Notify Java */
     jclass callback_cls = (*env)->GetObjectClass(env, callback);
@@ -440,9 +522,11 @@ Java_com_novoyuuparosk_iperf3gui_IperfRunner_forceStopIperfTest(
             env, callback_cls, "onOutput", "(Ljava/lang/String;)V");
     if (mid_output) {
         jstring msg = (*env)->NewStringUTF(env,
-                                           "[iPerf JNI] Requested graceful stop.");
-        (*env)->CallVoidMethod(env, callback, mid_output, msg);
-        (*env)->DeleteLocalRef(env, msg);
+                                           "[iPerf JNI] Requested graceful stop.\n");
+        if (msg) {
+            (*env)->CallVoidMethod(env, callback, mid_output, msg);
+            (*env)->DeleteLocalRef(env, msg);
+        }
     }
 }
 
@@ -453,7 +537,10 @@ Java_com_novoyuuparosk_iperf3gui_IperfRunner_forceStopIperfTest(
 JNIEXPORT jboolean JNICALL
 Java_com_novoyuuparosk_iperf3gui_IperfRunner_isTestRunning(JNIEnv *env,
                                                            jobject thiz) {
-    return (g_test != NULL && !g_test->done);
+    pthread_mutex_lock(&g_test_mutex);
+    jboolean running = (g_test != NULL && !g_test->done);
+    pthread_mutex_unlock(&g_test_mutex);
+    return running;
 }
 
 /* ------------------------------------------------------------------ */
diff --git a/android/app/src/main/kotlin/com/novoyuuparosk/iperf3gui/IperfRunner.kt b/android/app/src/main/kotlin/com/novoyuuparosk/iperf3gui/IperfRunner.kt
index 2e57025..988f81f 100644
--- a/android/app/src/main/kotlin/com/novoyuuparosk/iperf3gui/IperfRunner.kt
+++ b/android/app/src/main/kotlin/com/novoyuuparosk/iperf3gui/IperfRunner.kt
@@ -4,24 +4,38 @@ import android.os.Handler
 import android.os.Looper
 import io.flutter.embedding.engine.plugins.FlutterPlugin
 import io.flutter.plugin.common.MethodChannel
+import java.util.concurrent.Executors
 
 /**
  * Kotlin binding layer for native iperf3 via JNI.
  *
  * iperf3 runs natively inside the app process — no Process.start() needed,
- * no SELinux restrictions. Output is streamed live to the Flutter UI via
- * the IperfCallback interface, with all callbacks posted to the main thread.
+ * no SELinux restrictions.
+ *
+ * Threading: runIperfLive() blocks for the entire duration of the test, so it
+ * runs on a dedicated worker thread. Running it on the platform thread would
+ * freeze the UI and — because output is delivered by posting to the main
+ * looper — stall every callback until the test was already over.
  */
 object IperfRunner : FlutterPlugin {
 
+    private const val CHANNEL = "com.novoyuuparosk.iperf3gui/iperf"
+
     private var channel: MethodChannel? = null
     private var appContext: android.content.Context? = null
     private val mainHandler = Handler(Looper.getMainLooper())
 
+    /** Serialises test runs: one test at a time, off the platform thread. */
+    private val runExecutor =
+        Executors.newSingleThreadExecutor { r -> Thread(r, "iperf3-run") }
+
+    private var nativeLibraryLoaded = false
+
     init {
         try {
             android.util.Log.i("IperfRunner", "Loading native library...")
             System.loadLibrary("iperf3jni")
+            nativeLibraryLoaded = true
             android.util.Log.i("IperfRunner", "Native library loaded successfully")
         } catch (e: UnsatisfiedLinkError) {
             android.util.Log.e("IperfRunner", "Failed to load native library: ${e.message}")
@@ -31,62 +45,87 @@ object IperfRunner : FlutterPlugin {
 
     override fun onAttachedToEngine(binding: FlutterPlugin.FlutterPluginBinding) {
         appContext = binding.applicationContext
-        channel = MethodChannel(binding.binaryMessenger, "com.novoyuuparosk.iperf3gui/iperf")
+        channel = MethodChannel(binding.binaryMessenger, CHANNEL)
         channel?.setMethodCallHandler { call, result ->
             when (call.method) {
-                "runIperf" -> {
-                    val args = call.argument<List<String>>("args")?.toTypedArray()
-                    if (args != null) {
-                        // Set temp dir to app's cache dir — /data/local/tmp is NOT writable
-                        appContext?.cacheDir?.absolutePath?.let { cacheDir ->
-                            setTempDir(cacheDir)
-                        }
-                        // Wrap callbacks so they always run on the main thread.
-                        // The native reader thread cannot call invokeMethod directly.
-                        val safeCallback = MainThreadCallback(
-                            onOutput = { line ->
-                                channel?.invokeMethod("onOutput", mapOf("output" to line))
-                            },
-                            onError = { error ->
-                                channel?.invokeMethod("onError", mapOf("error" to error))
-                            },
-                            onComplete = {
-                                channel?.invokeMethod("onComplete", emptyMap<String, Any>())
-                            }
-                        )
-                        runIperfLive(args, safeCallback)
-                        result.success(null)
-                    } else {
-                        result.error("INVALID_ARGS", "args must be a String array", null)
-                    }
-                }
-                "stopIperf" -> {
-                    val safeCallback = MainThreadCallback(
-                        onOutput = { line ->
-                            channel?.invokeMethod("onOutput", mapOf("output" to line))
-                        },
-                        onError = { error ->
-                            channel?.invokeMethod("onError", mapOf("error" to error))
-                        },
-                        onComplete = {
-                            channel?.invokeMethod("onComplete", emptyMap<String, Any>())
-                        }
-                    )
-                    forceStopIperfTest(safeCallback)
-                    result.success(null)
-                }
-                "isTestRunning" -> {
-                    result.success(isTestRunning())
-                }
+                "runIperf" -> handleRunIperf(call.argument<List<String>>("args"), result)
+                "stopIperf" -> handleStopIperf(result)
+                "isTestRunning" -> result.success(nativeLibraryLoaded && isTestRunning())
                 else -> result.notImplemented()
             }
         }
     }
 
     override fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) {
+        // Stop any in-flight test: its callbacks would otherwise fire into a
+        // dead channel, and the worker thread would keep the socket open.
+        if (nativeLibraryLoaded && isTestRunning()) {
+            forceStopIperfTest(NoopCallback)
+        }
+        channel?.setMethodCallHandler(null)
         channel = null
+        appContext = null
     }
 
+    private fun handleRunIperf(args: List<String>?, result: MethodChannel.Result) {
+        if (!nativeLibraryLoaded) {
+            result.error(
+                "NATIVE_LIB_MISSING",
+                "libiperf3jni.so failed to load — cannot run iperf3",
+                null,
+            )
+            return
+        }
+        if (args == null) {
+            result.error("INVALID_ARGS", "args must be a String array", null)
+            return
+        }
+        if (isTestRunning()) {
+            result.error("ALREADY_RUNNING", "A test is already running", null)
+            return
+        }
+
+        // Set temp dir to the app's cache dir — mkstemp() in iperf_new_stream()
+        // cannot write to /data/local/tmp from inside the app sandbox.
+        appContext?.cacheDir?.absolutePath?.let { setTempDir(it) }
+
+        val argv = args.toTypedArray()
+        val callback = mainThreadCallback()
+
+        // Hand back control immediately; progress arrives via the callback.
+        result.success(null)
+
+        runExecutor.execute {
+            try {
+                runIperfLive(argv, callback)
+            } catch (t: Throwable) {
+                android.util.Log.e("IperfRunner", "runIperfLive threw", t)
+                callback.onError("Native error: ${t.message}")
+                callback.onComplete()
+            }
+        }
+    }
+
+    private fun handleStopIperf(result: MethodChannel.Result) {
+        if (!nativeLibraryLoaded) {
+            result.success(null)
+            return
+        }
+        forceStopIperfTest(mainThreadCallback())
+        result.success(null)
+    }
+
+    /**
+     * Build a callback that forwards native output to Dart, hopping to the
+     * main thread first: MethodChannel.invokeMethod must not be called from
+     * the native reader thread.
+     */
+    private fun mainThreadCallback(): IperfCallback = MainThreadCallback(
+        emitOutput = { line -> channel?.invokeMethod("onOutput", mapOf("output" to line)) },
+        emitError = { error -> channel?.invokeMethod("onError", mapOf("error" to error)) },
+        emitComplete = { channel?.invokeMethod("onComplete", emptyMap<String, Any>()) },
+    )
+
     // ─────────────────────────────────────────────────────────────────
     // Native method bindings
     // ─────────────────────────────────────────────────────────────────
@@ -107,23 +146,35 @@ object IperfRunner : FlutterPlugin {
     }
 
     /**
-     * Thread-safe wrapper: posts all callbacks to the main thread.
-     * This is required because the native reader thread cannot safely
-     * call MethodChannel.invokeMethod from a background thread.
+     * Posts every callback to the main thread.
+     *
+     * The lambdas are named `emit*` rather than `on*` on purpose: a constructor
+     * property with the same name as the overriding method would make
+     * `onOutput(line)` resolve back to this class's own method — an endless
+     * post-and-re-post loop that never reaches the channel.
      */
     private class MainThreadCallback(
-        private val onOutput: (String) -> Unit,
-        private val onError: (String) -> Unit,
-        private val onComplete: () -> Unit
+        private val emitOutput: (String) -> Unit,
+        private val emitError: (String) -> Unit,
+        private val emitComplete: () -> Unit,
     ) : IperfCallback {
         override fun onOutput(line: String) {
-            mainHandler.post { onOutput(line) }
+            mainHandler.post { emitOutput(line) }
         }
+
         override fun onError(error: String) {
-            mainHandler.post { onError(error) }
+            mainHandler.post { emitError(error) }
         }
+
         override fun onComplete() {
-            mainHandler.post { onComplete() }
+            mainHandler.post { emitComplete() }
         }
     }
-}
\ No newline at end of file
+
+    /** Used when a stop is requested with no channel left to report to. */
+    private object NoopCallback : IperfCallback {
+        override fun onOutput(line: String) = Unit
+        override fun onError(error: String) = Unit
+        override fun onComplete() = Unit
+    }
+}
diff --git a/docs/README.md b/docs/README.md
index a0bdc5d..321cfbc 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -11,9 +11,9 @@ lib/                          # Flutter/Dart application layer
 │   ├── models/
 │   │   ├── test_configuration.dart   # Server, port, duration, interval, parallel streams
 │   │   └── iperf3_result.dart        # Raw output + exit code
+├── data/
 │   └── services/
-│       ├── iperf3_service.dart       # Dart → MethodChannel bridge (async with Completer)
-│       └── iperf3_binary_path_provider.dart   # Deprecated (kept for reference)
+│       └── iperf3_service.dart       # Dart → MethodChannel bridge (async with Completer)
 └── ui/                       # Presentation layer
     └── features/
         └── test_run/
@@ -39,10 +39,11 @@ android/app/src/main/
 User taps GO
   → Dart TestRunViewModel.runTest(config)
   → Iperf3Service.run(config) via MethodChannel
-  → Kotlin IperfRunner.runIperfLive(args, callback)
-  → JNI C: java_string_array_to_argv() → iperf_parse_arguments()
-  → iperf_run_client(test)
-  → Reader thread pipes stdout → CallVoidMethod → Dart onOutput callbacks
+  → Kotlin IperfRunner: submits to the iperf3-run worker thread, returns at once
+  → JNI C: build_argv() (prepends argv[0]) → iperf_parse_arguments()
+  → iperf_run_client(test)             [blocks on the worker thread]
+  → Reader thread pipes output → CallVoidMethod → main-thread hop → Dart onOutput
+  → Dart streams each line to the UI via Iperf3Service.outputLines
   → On completion: Dart Completer resolves with Iperf3Result
 ```
 
@@ -51,11 +52,31 @@ User taps GO
 ### JNI Over Process Execution
 Android SELinux Enforcing mode blocks `execve()` from the `untrusted_app` domain, making Process.start() of external binaries fail with Permission denied. Compiling iperf3 as a shared library linked into the app process eliminates this restriction entirely — iperf3 code runs in-process with no domain transitions needed.
 
+### Threading
+`runIperfLive()` blocks for the whole test, so Kotlin submits it to a dedicated
+single-thread executor and hands control straight back to Dart. Running it on the
+Flutter platform thread froze the UI and — because output is delivered by posting
+to the main looper — stalled every callback until the test was already over.
+
 ### Callback Mechanism
 The JNI bridge uses `CallVoidMethod` on stored `jmethodID`s to invoke the Kotlin `IperfCallback` interface, NOT function pointer casts. Direct function pointer casts caused SIGBUS crashes on ARM due to JNINativeInterface method ID layout differences.
 
 ### Output Streaming
-iperf3 output is redirected via pipe to a background reader thread that attaches to the Java VM via `AttachCurrentThread` and invokes callbacks via `CallVoidMethod`. The reader thread frees the state struct on exit; the JNI caller owns the callback object's lifetime.
+iperf3 output is redirected via pipe to a background reader thread that attaches
+to the Java VM via `AttachCurrentThread` and invokes callbacks via
+`CallVoidMethod`. Dart re-publishes each line on `Iperf3Service.outputLines`, so
+the transcript grows while the test runs.
+
+The reader blocks in `fgets()` and only unblocks on EOF, so the pipe's write end
+must be closed **before** `pthread_join()` — joining first deadlocks the worker
+thread. The JNI caller solely owns the run-state struct and frees it after the
+join; the reader must never free it.
+
+### Stop Handling
+A stop shuts down the control socket, so `iperf_run_client()` returns -1 with
+"Broken pipe". That is the expected outcome of a stop, not a failure, so the
+bridge checks its own `g_stop` flag and reports a stop rather than an error; the
+flag travels up to the UI as `Iperf3Result.stopped`.
 
 ### Async Pattern
 Dart uses `Completer<Iperf3Result>` to await native completion. The MethodChannel callback handler resolves the completer on `onComplete`, with a timeout fallback that calls `stopIperf` on the native layer.
@@ -72,9 +93,10 @@ Dart uses `Completer<Iperf3Result>` to await native completion. The MethodChanne
 
 | Kotlin Method | JNI Signature | Purpose |
 |---|---|---|
-| `runIperfLive(String[], IperfCallback)` | `runIperfLive` | Start test with args and callback |
+| `runIperfLive(String[], IperfCallback)` | `runIperfLive` | Run a test to completion — blocks, call off the platform thread |
 | `forceStopIperfTest(IperfCallback)` | `forceStopIperfTest` | Graceful stop via shutdown() |
 | `isTestRunning()` | `isTestRunning` | Check if test is in progress |
+| `setTempDir(String)` | `setTempDir` | Point `mkstemp()` at the app cache dir |
 
 ## Building
 
@@ -93,7 +115,7 @@ adb install build/app/outputs/flutter-apk/app-debug.apk
 
 ## Dependencies
 
-- Dart: `provider`, `path_provider`
+- Dart: `provider`
 - Android: CMake external native build
 - Native: iperf3 3.19, cJSON (single file)
 
diff --git a/lib/data/services/iperf3_binary_path_provider.dart b/lib/data/services/iperf3_binary_path_provider.dart
deleted file mode 100644
index 05c5333..0000000
--- a/lib/data/services/iperf3_binary_path_provider.dart
+++ /dev/null
@@ -1,9 +0,0 @@
-// This file is kept as a stub — iperf3 is now compiled as a native
-// shared library (libiperf3jni.so) via JNI.
-// The old binary-path-provider pattern (extract ELF from assets → chmod → execve)
-// was replaced by the JNI approach after SELinux blocked binary execution.
-// See .hermes/plans/ for details on the migration.
-
-// The Iperf3Service now uses MethodChannel to communicate with Kotlin/JNI:
-//   Dart → MethodChannel → Kotlin → JNI → iperf3 (same process)
-// No file extraction, no chmod, no Process.start needed.
diff --git a/lib/data/services/iperf3_service.dart b/lib/data/services/iperf3_service.dart
index 2c22025..a3e6296 100644
--- a/lib/data/services/iperf3_service.dart
+++ b/lib/data/services/iperf3_service.dart
@@ -1,5 +1,4 @@
 import 'dart:async';
-import 'dart:io';
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
@@ -11,13 +10,38 @@ import 'package:iperf3gui/domain/models/test_configuration.dart';
 /// On Android, iperf3 is compiled into the app as a shared library (.so).
 /// This avoids SELinux restrictions on executing ELF binaries from assets.
 ///
-/// The service communicates with the native layer via a MethodChannel.
-/// Output is streamed live to the Flutter UI through callbacks.
+/// The service talks to the native layer over a MethodChannel. Native output
+/// arrives line by line on [outputLines] while the test runs; [run] resolves
+/// with the accumulated transcript once the native layer reports completion.
 class Iperf3Service {
+  Iperf3Service() {
+    _channel.setMethodCallHandler(_handleNativeCall);
+  }
+
   static const MethodChannel _channel =
       MethodChannel('com.novoyuuparosk.iperf3gui/iperf');
 
-  /// Collect output lines during a test run.
+  /// Exit code reported when the native layer signalled an error.
+  static const int exitCodeNativeError = 1;
+
+  /// Exit code reported when another test is already in flight.
+  static const int exitCodeBusy = -2;
+
+  /// Exit code reported when the test could not be started at all.
+  static const int exitCodeStartFailed = -1;
+
+  /// Exit code reported when the native layer never signalled completion.
+  static const int exitCodeTimeout = -3;
+
+  /// Lines emitted by the native layer during the current run.
+  final StreamController<String> _outputController =
+      StreamController<String>.broadcast();
+
+  /// Live output, one line per event. Use this to render progress; [run]'s
+  /// result carries the same text joined together.
+  Stream<String> get outputLines => _outputController.stream;
+
+  /// Transcript of the current (or most recent) run.
   final List<String> _outputBuffer = [];
 
   /// Completer that resolves when the native iperf3 test finishes.
@@ -25,13 +49,18 @@ class Iperf3Service {
 
   /// Whether iperf3 is currently running.
   bool _isRunning = false;
-
-  /// Whether iperf3 is currently running.
   bool get isRunning => _isRunning;
 
+  /// Whether the native layer reported an error during this run.
+  bool _sawError = false;
+
+  /// Whether [stop] was called for the current run.
+  bool _stopRequested = false;
+
   /// Cancel any running test.
   Future<void> stop() async {
     if (!_isRunning) return;
+    _stopRequested = true;
     try {
       await _channel.invokeMethod('stopIperf');
     } catch (e) {
@@ -39,104 +68,128 @@ class Iperf3Service {
     }
   }
 
+  /// Release the stream controller. Call from the owner's dispose().
+  Future<void> dispose() async {
+    _channel.setMethodCallHandler(null);
+    await _outputController.close();
+  }
+
   /// Run iperf3 with the given configuration.
   ///
-  /// Returns an [Iperf3Result] with stdout/stderr and exit code.
+  /// Returns an [Iperf3Result] with the full output and an exit code.
   Future<Iperf3Result> run(TestConfiguration config) async {
     if (_isRunning) {
-      return Iperf3Result(
+      return const Iperf3Result(
         rawOutput: 'Another test is already running.',
-        exitCode: -2,
+        exitCode: exitCodeBusy,
       );
     }
 
     _isRunning = true;
+    _sawError = false;
+    _stopRequested = false;
     _outputBuffer.clear();
 
-    final args = <String>[
-      '-c', config.server,
-      '-p', config.port.toString(),
-      '-t', config.duration.inSeconds.toString(),
-      '-i', config.interval.toString(),
-      '-P', config.parallelStreams.toString(),
-    ];
-
+    final args = config.toCliArgs();
     debugPrint('Iperf3Service: running: ${args.join(" ")}');
 
-    // Set up the completer to await completion
-    _runCompleter = Completer<Iperf3Result>();
+    final completer = Completer<Iperf3Result>();
+    _runCompleter = completer;
 
-    // Listen for events from native layer
-    _channel.setMethodCallHandler((call) async {
-      if (!_runCompleter!.isCompleted) {
-        switch (call.method) {
-          case 'onOutput':
-            final output = call.arguments['output'] as String?;
-            if (output != null) {
-              _outputBuffer.add(output);
-              debugPrint('Iperf3Service output: ${output.trim()}');
-            }
-            break;
-          case 'onError':
-            final error = call.arguments['error'] as String?;
-            if (error != null) {
-              debugPrint('Iperf3Service error: $error');
-              _outputBuffer.add('[ERROR] $error');
-              // Don't complete yet — the test might still be running
-            }
-            break;
-          case 'onComplete':
-            debugPrint('Iperf3Service: test completed');
-            _isRunning = false;
-            _runCompleter!.complete(
-              Iperf3Result(
-                rawOutput: _outputBuffer.join(''),
-                exitCode: 0,
-              ),
-            );
-            break;
-        }
-      }
-    });
-
-    // Start the test
     try {
       await _channel.invokeMethod('runIperf', {'args': args});
     } catch (e, stackTrace) {
       debugPrint('Iperf3Service exception: $e');
       debugPrint('Iperf3Service stack: $stackTrace');
-      _isRunning = false;
-      if (!_runCompleter!.isCompleted) {
-        _runCompleter!.completeError(e);
-      }
+      _finishRun();
       return Iperf3Result(
         rawOutput: 'Error starting iperf3: $e',
-        exitCode: -1,
+        exitCode: exitCodeStartFailed,
       );
     }
 
-    // Wait for the native layer to signal completion (with a timeout)
+    // Wait for the native layer to signal completion. The grace period covers
+    // DNS resolution and the 30s native connect timeout.
     try {
-      final result = await _runCompleter!.future.timeout(
-        config.duration + const Duration(seconds: 30),
+      return await completer.future.timeout(
+        config.duration + const Duration(seconds: 45),
         onTimeout: () {
           debugPrint('Iperf3Service: timeout, stopping test');
-          stop();
+          // Ask the native layer to wind down, then release local state so a
+          // stuck run can never lock the UI out of starting another test.
+          _channel.invokeMethod('stopIperf').catchError((Object e) {
+            debugPrint('Iperf3Service: error stopping after timeout: $e');
+            return null;
+          });
+          _emit('[ERROR] Timed out waiting for iperf3 to finish.');
           return Iperf3Result(
-            rawOutput: 'Test timed out after ${config.duration.inSeconds}s',
-            exitCode: -3,
+            rawOutput: _transcript(),
+            exitCode: exitCodeTimeout,
           );
         },
       );
-      return result;
     } catch (e) {
       debugPrint('Iperf3Service: error waiting for completion: $e');
       return Iperf3Result(
         rawOutput: 'Test failed: $e',
-        exitCode: -1,
+        exitCode: exitCodeStartFailed,
       );
     } finally {
-      _runCompleter = null;
+      _finishRun();
     }
   }
+
+  /// Handle a callback pushed up from the Kotlin/JNI layer.
+  Future<void> _handleNativeCall(MethodCall call) async {
+    switch (call.method) {
+      case 'onOutput':
+        final output = call.arguments['output'] as String?;
+        if (output != null) {
+          _emit(output);
+        }
+      case 'onError':
+        final error = call.arguments['error'] as String?;
+        if (error != null) {
+          // Not terminal on its own — iperf3 reports the failure reason and
+          // then completes, so wait for onComplete before resolving.
+          _sawError = true;
+          _emit('[ERROR] $error');
+        }
+      case 'onComplete':
+        debugPrint('Iperf3Service: test completed');
+        final completer = _runCompleter;
+        if (completer != null && !completer.isCompleted) {
+          completer.complete(
+            Iperf3Result(
+              rawOutput: _transcript(),
+              // A user-requested stop is a normal outcome, not a failure.
+              exitCode:
+                  (_sawError && !_stopRequested) ? exitCodeNativeError : 0,
+              stopped: _stopRequested,
+            ),
+          );
+        }
+      default:
+        debugPrint('Iperf3Service: unhandled native call ${call.method}');
+    }
+  }
+
+  void _emit(String line) {
+    _outputBuffer.add(line);
+    if (!_outputController.isClosed) {
+      _outputController.add(line);
+    }
+    debugPrint('Iperf3Service output: ${line.trimRight()}');
+  }
+
+  /// Native output already carries its own newlines; keep it verbatim except
+  /// for lines we synthesised ourselves.
+  String _transcript() => _outputBuffer
+      .map((line) => line.endsWith('\n') ? line : '$line\n')
+      .join();
+
+  void _finishRun() {
+    _isRunning = false;
+    _runCompleter = null;
+  }
 }
diff --git a/lib/domain/models/iperf3_result.dart b/lib/domain/models/iperf3_result.dart
index 2c54feb..ef1b990 100644
--- a/lib/domain/models/iperf3_result.dart
+++ b/lib/domain/models/iperf3_result.dart
@@ -3,8 +3,13 @@ class Iperf3Result {
   final String rawOutput;
   final int exitCode;
 
+  /// Whether the run ended because the user asked it to stop, rather than
+  /// finishing its configured duration or failing.
+  final bool stopped;
+
   const Iperf3Result({
     required this.rawOutput,
     required this.exitCode,
+    this.stopped = false,
   });
 }
diff --git a/lib/main.dart b/lib/main.dart
index 9a770a3..da2d2fb 100644
--- a/lib/main.dart
+++ b/lib/main.dart
@@ -1,5 +1,4 @@
 import 'package:flutter/material.dart';
-import 'package:iperf3gui/data/services/iperf3_service.dart';
 import 'package:iperf3gui/ui/features/test_run/test_run_screen.dart';
 
 /// Application entry point.
diff --git a/lib/ui/features/test_run/test_run_screen.dart b/lib/ui/features/test_run/test_run_screen.dart
index 715ca5f..fb2a85d 100644
--- a/lib/ui/features/test_run/test_run_screen.dart
+++ b/lib/ui/features/test_run/test_run_screen.dart
@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:provider/provider.dart';
 import 'package:iperf3gui/data/services/iperf3_service.dart';
 import 'package:iperf3gui/domain/models/test_configuration.dart';
@@ -6,8 +7,8 @@ import 'package:iperf3gui/ui/features/test_run/test_run_view_model.dart';
 
 /// Main test run screen.
 ///
-/// iperf3 is now compiled as a native shared library (libiperf3jni.so)
-/// and accessed via JNI. No binary extraction or chmod needed.
+/// iperf3 is compiled as a native shared library (libiperf3jni.so) and accessed
+/// via JNI, so there is no binary extraction or chmod step.
 class TestRunScreen extends StatelessWidget {
   const TestRunScreen({super.key});
 
@@ -30,109 +31,196 @@ class _TestRunContent extends StatefulWidget {
 }
 
 class _TestRunContentState extends State<_TestRunContent> {
-  final _serverController = TextEditingController(text: 'speedtest.uztelecom.uz');
-  final _portController = TextEditingController(text: '5201');
+  static const _defaults = TestConfiguration();
+
+  final _serverController =
+      TextEditingController(text: _defaults.server);
+  final _portController =
+      TextEditingController(text: _defaults.port.toString());
+  final _durationController =
+      TextEditingController(text: _defaults.duration.inSeconds.toString());
+  final _streamsController =
+      TextEditingController(text: _defaults.parallelStreams.toString());
+  final _outputScrollController = ScrollController();
 
   @override
   void dispose() {
     _serverController.dispose();
     _portController.dispose();
+    _durationController.dispose();
+    _streamsController.dispose();
+    _outputScrollController.dispose();
     super.dispose();
   }
 
+  TestConfiguration _readConfiguration() {
+    return TestConfiguration(
+      server: _serverController.text.trim(),
+      port: int.tryParse(_portController.text) ?? _defaults.port,
+      duration: Duration(
+        seconds: int.tryParse(_durationController.text) ??
+            _defaults.duration.inSeconds,
+      ),
+      parallelStreams:
+          int.tryParse(_streamsController.text) ?? _defaults.parallelStreams,
+    );
+  }
+
+  /// Keep the newest output in view, but only once the frame that added it has
+  /// been laid out.
+  void _scrollToBottom() {
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (!_outputScrollController.hasClients) return;
+      _outputScrollController
+          .jumpTo(_outputScrollController.position.maxScrollExtent);
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
         title: const Text('iperf3-gui'),
+        actions: [
+          Consumer<TestRunViewModel>(
+            builder: (context, vm, _) => IconButton(
+              tooltip: 'Copy output',
+              icon: const Icon(Icons.copy_all),
+              onPressed: vm.output.isEmpty
+                  ? null
+                  : () {
+                      Clipboard.setData(ClipboardData(text: vm.output));
+                      ScaffoldMessenger.of(context).showSnackBar(
+                        const SnackBar(content: Text('Output copied')),
+                      );
+                    },
+            ),
+          ),
+        ],
       ),
       body: Padding(
         padding: const EdgeInsets.all(16.0),
         child: Column(
           crossAxisAlignment: CrossAxisAlignment.stretch,
           children: [
-            // Server input
             TextField(
               controller: _serverController,
+              autocorrect: false,
               decoration: const InputDecoration(
                 labelText: 'Server',
                 hintText: 'e.g. iperf.es.net or 192.168.1.1',
               ),
             ),
-            const SizedBox(height: 16),
+            const SizedBox(height: 12),
 
-            // Port input
-            TextField(
-              controller: _portController,
-              decoration: const InputDecoration(
-                labelText: 'Port',
-                hintText: '5201',
-              ),
-              keyboardType: TextInputType.number,
-            ),
-            const SizedBox(height: 16),
-
-            // Go button
-            Consumer<TestRunViewModel>(
-              builder: (context, vm, _) {
-                return ElevatedButton(
-                  onPressed: vm.state == TestRunState.running
-                      ? null
-                      : () {
-                          final config = TestConfiguration(
-                            server: _serverController.text,
-                            port: int.tryParse(_portController.text) ?? 5201,
-                          );
-                          vm.runTest(config);
-                        },
-                  child: vm.state == TestRunState.running
-                      ? const SizedBox(
-                          width: 20,
-                          height: 20,
-                          child: CircularProgressIndicator(strokeWidth: 2),
-                        )
-                      : const Text('GO'),
-                );
-              },
-            ),
-            const SizedBox(height: 16),
-
-            // Status indicator
-            Consumer<TestRunViewModel>(
-              builder: (context, vm, _) {
-                final statusText = switch (vm.state) {
-                  TestRunState.idle => '',
-                  TestRunState.running => 'Running...',
-                  TestRunState.completed => 'Test complete',
-                  TestRunState.error => 'Error',
-                };
-                return Text(
-                  statusText,
-                  style: TextStyle(
-                    color: vm.state == TestRunState.error
-                        ? Colors.red
-                        : Colors.grey,
+            Row(
+              children: [
+                Expanded(
+                  child: TextField(
+                    controller: _portController,
+                    keyboardType: TextInputType.number,
+                    decoration: const InputDecoration(labelText: 'Port'),
                   ),
-                );
-              },
+                ),
+                const SizedBox(width: 12),
+                Expanded(
+                  child: TextField(
+                    controller: _durationController,
+                    keyboardType: TextInputType.number,
+                    decoration: const InputDecoration(labelText: 'Seconds'),
+                  ),
+                ),
+                const SizedBox(width: 12),
+                Expanded(
+                  child: TextField(
+                    controller: _streamsController,
+                    keyboardType: TextInputType.number,
+                    decoration: const InputDecoration(labelText: 'Streams'),
+                  ),
+                ),
+              ],
             ),
             const SizedBox(height: 16),
 
-            // Raw output text box
-            Expanded(
-              child: Consumer<TestRunViewModel>(
-                builder: (context, vm, _) {
-                  final output = vm.result?.rawOutput ?? '';
-                  return TextField(
-                    controller: TextEditingController(text: output),
-                    decoration: const InputDecoration(
-                      labelText: 'Raw Output',
-                      border: OutlineInputBorder(),
-                    ),
-                    maxLines: null,
-                    readOnly: true,
+            Consumer<TestRunViewModel>(
+              builder: (context, vm, _) {
+                if (vm.isRunning) {
+                  return OutlinedButton.icon(
+                    onPressed: vm.stopTest,
+                    icon: const Icon(Icons.stop),
+                    label: const Text('STOP'),
                   );
-                },
+                }
+                return ElevatedButton(
+                  onPressed: () => vm.runTest(_readConfiguration()),
+                  child: const Text('GO'),
+                );
+              },
+            ),
+            const SizedBox(height: 12),
+
+            // Status line
+            Consumer<TestRunViewModel>(
+              builder: (context, vm, _) {
+                final scheme = Theme.of(context).colorScheme;
+                final (String label, Color color) = switch (vm.state) {
+                  TestRunState.idle => ('Ready', scheme.onSurfaceVariant),
+                  TestRunState.running => ('Running…', scheme.primary),
+                  TestRunState.completed => (
+                      vm.wasStopped ? 'Stopped' : 'Test complete',
+                      vm.wasStopped ? scheme.onSurfaceVariant : scheme.primary,
+                    ),
+                  TestRunState.error => (
+                      'Error${vm.result != null ? ' (exit ${vm.result!.exitCode})' : ''}',
+                      scheme.error,
+                    ),
+                };
+                return Row(
+                  children: [
+                    if (vm.isRunning)
+                      const Padding(
+                        padding: EdgeInsets.only(right: 8),
+                        child: SizedBox(
+                          width: 14,
+                          height: 14,
+                          child: CircularProgressIndicator(strokeWidth: 2),
+                        ),
+                      ),
+                    Text(label, style: TextStyle(color: color)),
+                  ],
+                );
+              },
+            ),
+            const SizedBox(height: 12),
+
+            // Live output
+            Expanded(
+              child: Container(
+                width: double.infinity,
+                padding: const EdgeInsets.all(8),
+                decoration: BoxDecoration(
+                  border: Border.all(
+                    color: Theme.of(context).colorScheme.outlineVariant,
+                  ),
+                  borderRadius: BorderRadius.circular(4),
+                ),
+                child: Consumer<TestRunViewModel>(
+                  builder: (context, vm, _) {
+                    _scrollToBottom();
+                    return SingleChildScrollView(
+                      controller: _outputScrollController,
+                      child: SelectableText(
+                        vm.output.isEmpty
+                            ? 'Output will appear here.'
+                            : vm.output,
+                        style: const TextStyle(
+                          fontFamily: 'monospace',
+                          fontSize: 12,
+                        ),
+                      ),
+                    );
+                  },
+                ),
               ),
             ),
           ],
diff --git a/lib/ui/features/test_run/test_run_view_model.dart b/lib/ui/features/test_run/test_run_view_model.dart
index 04f2aa0..ec267ec 100644
--- a/lib/ui/features/test_run/test_run_view_model.dart
+++ b/lib/ui/features/test_run/test_run_view_model.dart
@@ -1,15 +1,26 @@
+import 'dart:async';
+
 import 'package:flutter/foundation.dart';
 import 'package:iperf3gui/data/services/iperf3_service.dart';
-import 'package:iperf3gui/domain/models/test_configuration.dart';
 import 'package:iperf3gui/domain/models/iperf3_result.dart';
+import 'package:iperf3gui/domain/models/test_configuration.dart';
 
 /// State of the test run.
 enum TestRunState { idle, running, completed, error }
 
 /// ViewModel for managing test run state.
+///
+/// Subscribes to [Iperf3Service.outputLines] so the transcript grows while the
+/// test runs rather than appearing all at once at the end.
 class TestRunViewModel extends ChangeNotifier {
   final Iperf3Service iperf3Service;
 
+  TestRunViewModel({required this.iperf3Service}) {
+    _outputSubscription = iperf3Service.outputLines.listen(_onOutputLine);
+  }
+
+  StreamSubscription<String>? _outputSubscription;
+
   TestRunState _state = TestRunState.idle;
   TestRunState get state => _state;
 
@@ -19,12 +30,28 @@ class TestRunViewModel extends ChangeNotifier {
   TestConfiguration? _currentConfig;
   TestConfiguration? get currentConfig => _currentConfig;
 
-  TestRunViewModel({required this.iperf3Service});
+  final StringBuffer _liveOutput = StringBuffer();
+
+  /// Output accumulated so far. Grows line by line during a run, and holds the
+  /// finished transcript once the test completes.
+  String get output => _liveOutput.toString();
+
+  /// Whether a test is currently in flight.
+  bool get isRunning => _state == TestRunState.running;
+
+  /// Whether the most recent finished run ended because the user stopped it.
+  bool get wasStopped => _result?.stopped ?? false;
 
   /// Start a test with the given configuration.
   Future<void> runTest(TestConfiguration config) async {
+    if (_state == TestRunState.running) return;
+
     if (!config.isValid) {
+      _liveOutput
+        ..clear()
+        ..writeln('Invalid configuration: check the server address and port.');
       _state = TestRunState.error;
+      _result = null;
       notifyListeners();
       return;
     }
@@ -32,26 +59,51 @@ class TestRunViewModel extends ChangeNotifier {
     _state = TestRunState.running;
     _currentConfig = config;
     _result = null;
+    _liveOutput.clear();
     notifyListeners();
 
     try {
       final result = await iperf3Service.run(config);
       _result = result;
-      _state = result.exitCode == 0
-          ? TestRunState.completed
-          : TestRunState.error;
+      // Prefer the streamed transcript — it is what the user watched build up.
+      // Fall back to the service's copy if nothing streamed through.
+      if (_liveOutput.isEmpty && result.rawOutput.isNotEmpty) {
+        _liveOutput.write(result.rawOutput);
+      }
+      _state =
+          result.exitCode == 0 ? TestRunState.completed : TestRunState.error;
     } catch (e) {
+      _liveOutput.writeln('Test failed: $e');
       _state = TestRunState.error;
     } finally {
       notifyListeners();
     }
   }
 
+  /// Request that a running test stop early.
+  Future<void> stopTest() async {
+    if (_state != TestRunState.running) return;
+    await iperf3Service.stop();
+  }
+
   /// Reset to idle state.
   void reset() {
     _state = TestRunState.idle;
     _result = null;
     _currentConfig = null;
+    _liveOutput.clear();
     notifyListeners();
   }
+
+  void _onOutputLine(String line) {
+    _liveOutput.write(line.endsWith('\n') ? line : '$line\n');
+    notifyListeners();
+  }
+
+  @override
+  void dispose() {
+    _outputSubscription?.cancel();
+    iperf3Service.dispose();
+    super.dispose();
+  }
 }
diff --git a/linux/flutter/generated_plugins.cmake b/linux/flutter/generated_plugins.cmake
index be1ee3e..2e1de87 100644
--- a/linux/flutter/generated_plugins.cmake
+++ b/linux/flutter/generated_plugins.cmake
@@ -6,7 +6,6 @@ list(APPEND FLUTTER_PLUGIN_LIST
 )
 
 list(APPEND FLUTTER_FFI_PLUGIN_LIST
-  jni
 )
 
 set(PLUGIN_BUNDLED_LIBRARIES)
diff --git a/pubspec.lock b/pubspec.lock
index 9b71df9..a4537c9 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -1,14 +1,6 @@
 # Generated by pub
 # See https://dart.dev/tools/pub/glossary#lockfile
 packages:
-  args:
-    dependency: transitive
-    description:
-      name: args
-      sha256: d0481093c50b1da8910eb0bb301626d4d8eb7284aa739614d2b394ee09e3ea04
-      url: "https://pub.dev"
-    source: hosted
-    version: "2.7.0"
   async:
     dependency: transitive
     description:
@@ -41,14 +33,6 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.1.2"
-  code_assets:
-    dependency: transitive
-    description:
-      name: code_assets
-      sha256: bf394f466ba9205f1812a0433b392d6af280f155f56651eda7c18cc32ed493b8
-      url: "https://pub.dev"
-    source: hosted
-    version: "1.2.1"
   collection:
     dependency: transitive
     description:
@@ -57,14 +41,6 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.19.1"
-  crypto:
-    dependency: transitive
-    description:
-      name: crypto
-      sha256: c8ea0233063ba03258fbcf2ca4d6dadfefe14f02fab57702265467a19f27fadf
-      url: "https://pub.dev"
-    source: hosted
-    version: "3.0.7"
   fake_async:
     dependency: transitive
     description:
@@ -73,14 +49,6 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.3.3"
-  ffi:
-    dependency: transitive
-    description:
-      name: ffi
-      sha256: "6d7fd89431262d8f3125e81b50d3847a091d846eafcd4fdb88dd06f36d705a45"
-      url: "https://pub.dev"
-    source: hosted
-    version: "2.2.0"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -99,38 +67,6 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
-  hooks:
-    dependency: transitive
-    description:
-      name: hooks
-      sha256: "9a62a50b50b769a737bc0a8ff381f333529df3ab746b2f6b02e83760231455ba"
-      url: "https://pub.dev"
-    source: hosted
-    version: "2.0.2"
-  jni:
-    dependency: transitive
-    description:
-      name: jni
-      sha256: f038e58b4dc2c9037f50e233175086337e0b305e356d28211bf55f21c504cbd3
-      url: "https://pub.dev"
-    source: hosted
-    version: "1.0.3"
-  jni_flutter:
-    dependency: transitive
-    description:
-      name: jni_flutter
-      sha256: "7b717011ea40d04fd47c2731d3d1d36eb99eba3435c2753d62489e8c3c9991d5"
-      url: "https://pub.dev"
-    source: hosted
-    version: "1.0.2"
-  jni_util:
-    dependency: transitive
-    description:
-      name: jni_util
-      sha256: "1ba86da04a5f2bf18fde2edb235587e70c5b0fc5bd4ba955f46b00942c3fc35f"
-      url: "https://pub.dev"
-    source: hosted
-    version: "1.0.0"
   leak_tracker:
     dependency: transitive
     description:
@@ -163,14 +99,6 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "6.1.0"
-  logging:
-    dependency: transitive
-    description:
-      name: logging
-      sha256: c8245ada5f1717ed44271ed1c26b8ce85ca3228fd2ffdb75468ab01979309d61
-      url: "https://pub.dev"
-    source: hosted
-    version: "1.3.0"
   matcher:
     dependency: transitive
     description:
@@ -203,22 +131,6 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.0.0"
-  objective_c:
-    dependency: transitive
-    description:
-      name: objective_c
-      sha256: b7fb95a6d9a4f009edd63dc5ac69f07420b23a16161c6dd8660290b59c602e8e
-      url: "https://pub.dev"
-    source: hosted
-    version: "9.5.0"
-  package_config:
-    dependency: transitive
-    description:
-      name: package_config
-      sha256: ffcf4cf3d6c0b74ac43708d9f56625506e8a68aa935abe9d267a7330f320eb5d
-      url: "https://pub.dev"
-    source: hosted
-    version: "3.0.0"
   path:
     dependency: transitive
     description:
@@ -227,70 +139,6 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.9.1"
-  path_provider:
-    dependency: "direct main"
-    description:
-      name: path_provider
-      sha256: a7f4874f987173da295a61c181b8ee71dab59b332a486b391babf26a1b884825
-      url: "https://pub.dev"
-    source: hosted
-    version: "2.1.6"
-  path_provider_android:
-    dependency: transitive
-    description:
-      name: path_provider_android
-      sha256: "69cbd515a62b94d32a7944f086b2f82b4ac40a1d45bebfc00813a430ab2dabcd"
-      url: "https://pub.dev"
-    source: hosted
-    version: "2.3.1"
-  path_provider_foundation:
-    dependency: transitive
-    description:
-      name: path_provider_foundation
-      sha256: "2a376b7d6392d80cd3705782d2caa734ca4727776db0b6ec36ef3f1855197699"
-      url: "https://pub.dev"
-    source: hosted
-    version: "2.6.0"
-  path_provider_linux:
-    dependency: transitive
-    description:
-      name: path_provider_linux
-      sha256: "58c2005f147315b11e9b4a7bc889cd5203e250cba8e3f012dae259b4972b5c16"
-      url: "https://pub.dev"
-    source: hosted
-    version: "2.2.2"
-  path_provider_platform_interface:
-    dependency: transitive
-    description:
-      name: path_provider_platform_interface
-      sha256: "484838772624c3a4b94f1e44a3e19897fee738f2d5c4ce448443b0417f7c9dda"
-      url: "https://pub.dev"
-    source: hosted
-    version: "2.1.3"
-  path_provider_windows:
-    dependency: transitive
-    description:
-      name: path_provider_windows
-      sha256: bd6f00dbd873bfb70d0761682da2b3a2c2fccc2b9e84c495821639601d81afe7
-      url: "https://pub.dev"
-    source: hosted
-    version: "2.3.0"
-  platform:
-    dependency: transitive
-    description:
-      name: platform
-      sha256: "5d6b1b0036a5f331ebc77c850ebc8506cbc1e9416c27e59b439f917a902a4984"
-      url: "https://pub.dev"
-    source: hosted
-    version: "3.1.6"
-  plugin_platform_interface:
-    dependency: transitive
-    description:
-      name: plugin_platform_interface
-      sha256: "4820fbfdb9478b1ebae27888254d445073732dae3d6ea81f0b7e06d5dedc3f02"
-      url: "https://pub.dev"
-    source: hosted
-    version: "2.1.8"
   provider:
     dependency: "direct main"
     description:
@@ -299,22 +147,6 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "6.1.5+1"
-  pub_semver:
-    dependency: transitive
-    description:
-      name: pub_semver
-      sha256: "5bfcf68ca79ef689f8990d1160781b4bad40a3bd5e5218ad4076ddb7f4081585"
-      url: "https://pub.dev"
-    source: hosted
-    version: "2.2.0"
-  record_use:
-    dependency: transitive
-    description:
-      name: record_use
-      sha256: "2551bd8eecfe95d14ae75f6021ad0248be5c27f138c2ec12fcb52b500b3ba1ed"
-      url: "https://pub.dev"
-    source: hosted
-    version: "0.6.0"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -368,14 +200,6 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "0.7.12"
-  typed_data:
-    dependency: transitive
-    description:
-      name: typed_data
-      sha256: f9049c039ebfeb4cf7a7104a675823cd72dba8297f264b6637062516699fa006
-      url: "https://pub.dev"
-    source: hosted
-    version: "1.4.0"
   vector_math:
     dependency: transitive
     description:
@@ -392,22 +216,6 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "15.3.0"
-  xdg_directories:
-    dependency: transitive
-    description:
-      name: xdg_directories
-      sha256: "7a3f37b05d989967cdddcbb571f1ea834867ae2faa29725fd085180e0883aa15"
-      url: "https://pub.dev"
-    source: hosted
-    version: "1.1.0"
-  yaml:
-    dependency: transitive
-    description:
-      name: yaml
-      sha256: b9da305ac7c39faa3f030eccd175340f968459dae4af175130b3fc47e40d76ce
-      url: "https://pub.dev"
-    source: hosted
-    version: "3.1.3"
 sdks:
   dart: ">=3.13.1 <4.0.0"
-  flutter: ">=3.38.4"
+  flutter: ">=3.18.0-18.0.pre.54"
diff --git a/pubspec.yaml b/pubspec.yaml
index f12b5ee..3af8d77 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -11,7 +11,6 @@ dependencies:
   flutter:
     sdk: flutter
 
-  path_provider: ^2.1.4
   provider: ^6.1.2
 
 dev_dependencies:
diff --git a/test/domain/models/iperf3_result_test.dart b/test/domain/models/iperf3_result_test.dart
index 68567d7..89070e7 100644
--- a/test/domain/models/iperf3_result_test.dart
+++ b/test/domain/models/iperf3_result_test.dart
@@ -11,5 +11,15 @@ void main() {
       expect(result.rawOutput, equals('Test complete'));
       expect(result.exitCode, equals(0));
     });
+
+    test('stopped defaults to false', () {
+      const result = Iperf3Result(rawOutput: 'x', exitCode: 0);
+      expect(result.stopped, isFalse);
+    });
+
+    test('stopped is preserved when set', () {
+      const result = Iperf3Result(rawOutput: 'x', exitCode: 0, stopped: true);
+      expect(result.stopped, isTrue);
+    });
   });
 }
diff --git a/test/ui/features/test_run/test_run_view_model_test.dart b/test/ui/features/test_run/test_run_view_model_test.dart
index 46b7532..6f83d36 100644
--- a/test/ui/features/test_run/test_run_view_model_test.dart
+++ b/test/ui/features/test_run/test_run_view_model_test.dart
@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:flutter_test/flutter_test.dart';
 import 'package:iperf3gui/data/services/iperf3_service.dart';
 import 'package:iperf3gui/domain/models/iperf3_result.dart';
@@ -7,29 +9,26 @@ import 'package:iperf3gui/ui/features/test_run/test_run_view_model.dart';
 void main() {
   group('TestRunViewModel', () {
     test('starts in idle state', () {
-      final vm = TestRunViewModel(
-        iperf3Service: _MockIperf3Service(),
-      );
+      final vm = TestRunViewModel(iperf3Service: _MockIperf3Service());
       expect(vm.state, equals(TestRunState.idle));
       expect(vm.result, isNull);
       expect(vm.currentConfig, isNull);
+      expect(vm.output, isEmpty);
     });
 
     test('can be reset', () {
-      final vm = TestRunViewModel(
-        iperf3Service: _MockIperf3Service(),
-      );
+      final vm = TestRunViewModel(iperf3Service: _MockIperf3Service());
       vm.reset();
       expect(vm.state, equals(TestRunState.idle));
     });
 
     test('invalid config sets error state without running', () async {
-      final vm = TestRunViewModel(
-        iperf3Service: _MockIperf3Service(),
-      );
+      final mock = _MockIperf3Service();
+      final vm = TestRunViewModel(iperf3Service: mock);
       const config = TestConfiguration(server: '');
       await vm.runTest(config);
       expect(vm.state, equals(TestRunState.error));
+      expect(mock.runCallCount, equals(0));
     });
 
     test('runTest with valid config calls service', () async {
@@ -45,17 +44,165 @@ void main() {
       expect(vm.state, equals(TestRunState.completed));
       expect(vm.result, isNotNull);
     });
+
+    test('non-zero exit code lands in error state', () async {
+      final mock = _MockIperf3Service(
+        onRun: (_) async =>
+            const Iperf3Result(rawOutput: 'boom', exitCode: 1),
+      );
+      final vm = TestRunViewModel(iperf3Service: mock);
+      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+      expect(vm.state, equals(TestRunState.error));
+      expect(vm.result!.exitCode, equals(1));
+    });
+
+    test('streamed lines accumulate into output during the run', () async {
+      final mock = _MockIperf3Service();
+      mock.onRun = (_) async {
+        mock.emit('Connecting to host 192.168.1.1\n');
+        mock.emit('[  5]   0.00-1.00   sec  11.2 MBytes  94.1 Mbits/sec\n');
+        // Let the broadcast stream deliver before the run resolves.
+        await Future<void>.delayed(Duration.zero);
+        return const Iperf3Result(rawOutput: 'ignored', exitCode: 0);
+      };
+
+      final vm = TestRunViewModel(iperf3Service: mock);
+      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+
+      expect(vm.output, contains('Connecting to host'));
+      expect(vm.output, contains('94.1 Mbits/sec'));
+      // The streamed transcript wins over the service's own copy.
+      expect(vm.output, isNot(contains('ignored')));
+    });
+
+    test('falls back to result output when nothing streamed', () async {
+      final mock = _MockIperf3Service(
+        onRun: (_) async =>
+            const Iperf3Result(rawOutput: 'summary only', exitCode: 0),
+      );
+      final vm = TestRunViewModel(iperf3Service: mock);
+      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+      expect(vm.output, contains('summary only'));
+    });
+
+    test('output is cleared when a new run starts', () async {
+      final mock = _MockIperf3Service(
+        onRun: (_) async =>
+            const Iperf3Result(rawOutput: 'first', exitCode: 0),
+      );
+      final vm = TestRunViewModel(iperf3Service: mock);
+      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+      expect(vm.output, contains('first'));
+
+      mock.onRun = (_) async =>
+          const Iperf3Result(rawOutput: 'second', exitCode: 0);
+      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+      expect(vm.output, isNot(contains('first')));
+      expect(vm.output, contains('second'));
+    });
+
+    test('stopTest forwards to the service only while running', () async {
+      final mock = _MockIperf3Service();
+      final vm = TestRunViewModel(iperf3Service: mock);
+
+      await vm.stopTest();
+      expect(mock.stopCallCount, equals(0), reason: 'idle: nothing to stop');
+
+      final gate = Completer<Iperf3Result>();
+      mock.onRun = (_) => gate.future;
+      final run = vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+      expect(vm.isRunning, isTrue);
+
+      await vm.stopTest();
+      expect(mock.stopCallCount, equals(1));
+
+      gate.complete(const Iperf3Result(rawOutput: 'stopped', exitCode: 0));
+      await run;
+    });
+
+    test('wasStopped reflects a user-requested stop', () async {
+      final mock = _MockIperf3Service(
+        onRun: (_) async => const Iperf3Result(
+          rawOutput: 'stopped early',
+          exitCode: 0,
+          stopped: true,
+        ),
+      );
+      final vm = TestRunViewModel(iperf3Service: mock);
+      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+      // A user stop is a normal outcome: completed, not error.
+      expect(vm.state, equals(TestRunState.completed));
+      expect(vm.wasStopped, isTrue);
+    });
+
+    test('wasStopped is false for a run that finished on its own', () async {
+      final mock = _MockIperf3Service(
+        onRun: (_) async =>
+            const Iperf3Result(rawOutput: 'done', exitCode: 0),
+      );
+      final vm = TestRunViewModel(iperf3Service: mock);
+      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+      expect(vm.wasStopped, isFalse);
+    });
+
+    test('a second runTest while running is ignored', () async {
+      final mock = _MockIperf3Service();
+      final gate = Completer<Iperf3Result>();
+      mock.onRun = (_) => gate.future;
+
+      final vm = TestRunViewModel(iperf3Service: mock);
+      final run = vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+      expect(mock.runCallCount, equals(1));
+
+      gate.complete(const Iperf3Result(rawOutput: 'done', exitCode: 0));
+      await run;
+    });
   });
 }
 
 class _MockIperf3Service implements Iperf3Service {
   _MockIperf3Service({this.onRun});
 
-  final Future<Iperf3Result> Function(TestConfiguration)? onRun;
+  Future<Iperf3Result> Function(TestConfiguration)? onRun;
+
+  final StreamController<String> _controller =
+      StreamController<String>.broadcast();
+
+  int runCallCount = 0;
+  int stopCallCount = 0;
+  bool disposed = false;
+  bool _isRunning = false;
+
+  /// Push a line as if the native layer had emitted it.
+  void emit(String line) => _controller.add(line);
+
+  @override
+  Stream<String> get outputLines => _controller.stream;
+
+  @override
+  bool get isRunning => _isRunning;
 
   @override
   Future<Iperf3Result> run(TestConfiguration config) async {
-    if (onRun != null) return onRun!(config);
-    return const Iperf3Result(rawOutput: '', exitCode: 0);
+    runCallCount++;
+    _isRunning = true;
+    try {
+      if (onRun != null) return await onRun!(config);
+      return const Iperf3Result(rawOutput: '', exitCode: 0);
+    } finally {
+      _isRunning = false;
+    }
+  }
+
+  @override
+  Future<void> stop() async {
+    stopCallCount++;
+  }
+
+  @override
+  Future<void> dispose() async {
+    disposed = true;
+    await _controller.close();
   }
 }
diff --git a/windows/flutter/generated_plugins.cmake b/windows/flutter/generated_plugins.cmake
index 3ad69c6..b93c4c3 100644
--- a/windows/flutter/generated_plugins.cmake
+++ b/windows/flutter/generated_plugins.cmake
@@ -6,7 +6,6 @@ list(APPEND FLUTTER_PLUGIN_LIST
 )
 
 list(APPEND FLUTTER_FFI_PLUGIN_LIST
-  jni
 )
 
 set(PLUGIN_BUNDLED_LIBRARIES)