diff --git a/client/platform/desktop/backend/native/interactive.ts b/client/platform/desktop/backend/native/interactive.ts
index 3df410405..ab1a8ac74 100644
--- a/client/platform/desktop/backend/native/interactive.ts
+++ b/client/platform/desktop/backend/native/interactive.ts
@@ -201,12 +201,15 @@ export class InteractiveServiceManager extends EventEmitter {
       const segConfig = npath.join(pipelines, 'interactive_segmenter_default.conf');
       const stereoConfig = npath.join(pipelines, 'interactive_stereo_default.conf');
 
-      // -I: isolated mode — do not prepend the process cwd to sys.path. Without
-      // this, a sibling folder named "coverage" (e.g. Vitest HTML output under
-      // client/coverage/) shadows Python's coverage package, breaks numba import,
-      // and prevents ocv_watershed from registering during plugin load.
+      // -s: ignore the per-user site-packages dir so a stray package in
+      // ~/.local (e.g. a conflicting "coverage" that breaks numba import and
+      // prevents ocv_watershed from registering) can't shadow VIAME's. We can't
+      // use -I/-E here: those also discard PYTHONPATH, which setup_viame.sh uses
+      // to expose the viame module in from-source/system-python builds. The
+      // process cwd is forced to viamePath (below), which has no shadowing
+      // modules, so the cwd entry on sys.path is harmless.
       const pyCommand = [
-        `"${pythonExe}" -I -m viame.core.interactive_service`,
+        `"${pythonExe}" -s -m viame.core.interactive_service`,
         `--segmentation-config "${segConfig}"`,
         `--stereo-config "${stereoConfig}"`,
       ].join(' ');
@@ -456,11 +459,19 @@ export class InteractiveServiceManager extends EventEmitter {
     settings: Settings,
     calibration?: StereoCalibration,
     calibrationFile?: string,
-  ): Promise<{ success: boolean; error?: string }> {
+  ): Promise<{ success: boolean; error?: string; launchFailed?: boolean }> {
     try {
       await this.ensureStarted(settings);
     } catch (err) {
-      return { success: false, error: err instanceof Error ? err.message : String(err) };
+      // The service process couldn't even start (missing interpreter, import
+      // failure, etc.). This is an infrastructure error, distinct from a benign
+      // per-dataset enable failure (e.g. missing calibration), so flag it so the
+      // caller always surfaces it rather than degrading silently.
+      return {
+        success: false,
+        launchFailed: true,
+        error: err instanceof Error ? err.message : String(err),
+      };
     }
     try {
       const response = await this.sendRequest({
diff --git a/client/platform/desktop/backend/native/linux.ts b/client/platform/desktop/backend/native/linux.ts
index 77041b879..1bc3a077e 100644
--- a/client/platform/desktop/backend/native/linux.ts
+++ b/client/platform/desktop/backend/native/linux.ts
@@ -65,7 +65,14 @@ function getViameConstants(settings: Settings): viame.ViameConstants {
 }
 
 function getViamePythonExe(settings: Settings): string {
-  return npath.join(settings.viamePath, 'bin', 'python');
+  // Packaged binary installs bundle an interpreter at bin/python. From-source
+  // builds against system python have no such interpreter and instead rely on
+  // setup_viame.sh putting the correct python on PATH, so fall back to that.
+  const bundled = npath.join(settings.viamePath, 'bin', 'python');
+  if (fs.existsSync(bundled)) {
+    return bundled;
+  }
+  return 'python';
 }
 
 async function validateViamePath(settings: Settings): Promise<true | string> {
diff --git a/client/platform/desktop/frontend/api.ts b/client/platform/desktop/frontend/api.ts
index 7d6acd865..4f1fb1c71 100644
--- a/client/platform/desktop/frontend/api.ts
+++ b/client/platform/desktop/frontend/api.ts
@@ -440,7 +440,7 @@ interface StereoTransferPointsResponse {
 async function stereoEnable(
   calibration?: StereoCalibration,
   calibrationFile?: string,
-): Promise<{ success: boolean; error?: string }> {
+): Promise<{ success: boolean; error?: string; launchFailed?: boolean }> {
   return window.diveDesktop.invoke('stereo-enable', { calibration, calibrationFile });
 }
 
diff --git a/client/platform/desktop/frontend/components/ViewerLoader.vue b/client/platform/desktop/frontend/components/ViewerLoader.vue
index a56d6f900..a24099282 100644
--- a/client/platform/desktop/frontend/components/ViewerLoader.vue
+++ b/client/platform/desktop/frontend/components/ViewerLoader.vue
@@ -442,7 +442,14 @@ export default defineComponent({
           }
           const result = await stereoEnable(undefined, stereoCalibrationFile);
           if (!result.success) {
-            throw new Error(result.error || 'Failed to enable stereo service');
+            // launchFailed means the backend service couldn't even start (e.g.
+            // missing python interpreter or a broken import). That is a real
+            // error and must always be surfaced, even on the load-time
+            // auto-enable, instead of degrading silently like a missing
+            // calibration would.
+            const err = new Error(result.error || 'Failed to enable stereo service');
+            (err as Error & { launchFailed?: boolean }).launchFailed = result.launchFailed;
+            throw err;
           }
           stereoEnabled.value = true;
           stereoLoadingDialog.value = false;
@@ -454,15 +461,18 @@ export default defineComponent({
         } catch (err) {
           stereoEnabled.value = false;
           console.error('[Stereo] Failed to enable interactive stereo:', err);
-          if (userInitiated) {
-            // The user explicitly enabled a feature: revert the toggles and
-            // surface the failure in a dialog.
+          const launchFailed = (err as Error & { launchFailed?: boolean }).launchFailed === true;
+          if (userInitiated || launchFailed) {
+            // The user explicitly enabled a feature, or the backend service
+            // failed to launch (an infrastructure error). Either way, revert the
+            // toggles and surface the failure in a dialog.
             disableStereoFeatureToggles();
             stereoLoadingError.value = err instanceof Error ? err.message : String(err);
             stereoLoadingDialog.value = true;
           } else {
-            // Load-time auto-enable failed: degrade silently and keep the
-            // toggle states so a later calibrated dataset still works.
+            // Load-time auto-enable failed for a benign reason (e.g. an
+            // uncalibrated stereo dataset): degrade silently and keep the toggle
+            // states so a later calibrated dataset still works.
             stereoLoadingDialog.value = false;
           }
         }