Preplanner: surface plan failures so the Processing dialog exits

When a plan fails (e.g. AuxPreprocessor Z-A coupling rejection at
planner-load time, or any other gplan error in the plan.py
subprocess), the Plan future was never resolved. PathHandler then
1-second-times-out forever returning {progress:0}, and the JS poll
loop in load_toolpath kept the 'Processing New File' dialog up
indefinitely.

- Preplanner.Plan now records .error and always resolves the future.
- PathHandler returns {progress:1, error:...} when the plan failed.
- load_toolpath closes the dialog and alerts the operator on error,
  and breaks out of the poll loop on api errors instead of looping.
- FileHandler upload-time AuxPreprocessor coupling errors now post a
  visible state message instead of being silently swallowed.

src/js/program-mixin.js

@@ -232,6 +232,17 @@ module.exports = {
           const toolpath = await api.get(`path/${file}`);
           this.toolpath_progress = toolpath.progress;
 
+          // Planner failure (e.g. AuxPreprocessor Z-A coupling
+          // rejection). Close the dialog and surface the message
+          // instead of polling the same broken plan forever.
+          if (toolpath.error) {
+            this.showGcodeMessage = false;
+            this.toolpath_progress = 0;
+            console.error("Plan failed:", toolpath.error);
+            alert("Could not plan G-code:\n\n" + toolpath.error);
+            return;
+          }
+
           if (toolpath.progress === 1 || typeof toolpath.progress == "undefined") {
             this.showGcodeMessage = false;
 
@@ -248,7 +259,11 @@ module.exports = {
             }
           }
         } catch (error) {
+          // api.get throws on non-2xx; log and break the loop so the
+          // dialog doesn't stay up forever.
           console.error(error);
+          this.showGcodeMessage = false;
+          return;
         }
       }
     },

src/py/bbctrl/FileHandler.py

@@ -107,15 +107,27 @@ class FileHandler(bbctrl.APIHandler):
             # auxcnc stepper is exposed as a virtual A axis (see
             # ExternalAxis).
             try:
-                from bbctrl.AuxPreprocessor import preprocess_file
+                from bbctrl.AuxPreprocessor import (
+                    preprocess_file, AuxPreprocessorError)
                 log = self.get_log('AuxPreprocessor')
                 ext = getattr(self.get_ctrl(), 'ext_axis', None)
                 coupling = (ext.coupling_for_preprocessor()
                             if ext is not None else None)
+                try:
                     if preprocess_file(filename.decode('utf8'),
                                        log=log, coupling=coupling):
                         log.info('Rewrote upload (ATC / Z-A coupling) in %s'
                                  % self.uploadFilename)
+                except AuxPreprocessorError as e:
+                    # Surface coupling-violation errors to the operator
+                    # via the message stream so the upload doesn't go
+                    # silently un-rewritten and then trip the runtime
+                    # check (which can hang the planner dialog).
+                    log.warning('Aux preprocess refused upload: %s' % e)
+                    try:
+                        self.get_ctrl().state.add_message(
+                            'Z-A coupling: ' + str(e))
+                    except Exception: pass
             except Exception:
                 self.get_log('AuxPreprocessor').exception(
                     'Aux preprocess failed; uploading unchanged')

src/py/bbctrl/Preplanner.py

@@ -74,6 +74,7 @@ class Plan(object):
         self.progress = 0
         self.cancel = False
         self.pid = None
+        self.error = None
 
         root = ctrl.get_path()
         self.gcode = '%s/upload/%s' % (root, filename)
@@ -202,8 +203,16 @@ class Plan(object):
             if not self._exists(): yield self._exec()
             self.future.set_result(self._read())
 
-        except:
+        except Exception as e:
-            self.preplanner.log.exception("Failed to load file - doesn't appear to be GCode.")
+            # Record the error and ALWAYS resolve the future, otherwise
+            # PathHandler.get keeps timing out at 1s forever and the UI
+            # gets stuck on the "Processing New File" dialog.
+            self.preplanner.log.exception(
+                "Failed to plan file: " + str(e))
+            self.error = str(e) or 'Plan failed'
+            self.progress = 1
+            if not self.future.done():
+                self.future.set_result(None)
 
 
 class Preplanner(object):
@@ -268,3 +277,6 @@ class Preplanner(object):
 
     def get_plan_progress(self, filename):
         return self.plans[filename].progress if filename in self.plans else 0
+
+    def get_plan_error(self, filename):
+        return self.plans[filename].error if filename in self.plans else None

src/py/bbctrl/Web.py

@@ -411,11 +411,22 @@ class PathHandler(bbctrl.APIHandler):
 
         except gen.TimeoutError:
             progress = preplanner.get_plan_progress(filename)
-            self.write_json(dict(progress = progress))
+            err = preplanner.get_plan_error(filename)
+            resp = dict(progress = progress)
+            if err: resp['error'] = err
+            self.write_json(resp)
             return
 
         try:
-            if data is None: return
+            # Plan finished but produced no data (planner subprocess
+            # failed, e.g. AuxPreprocessor coupling rejection at
+            # planner-load time). Surface the error so the UI can
+            # close the "Processing New File" dialog instead of
+            # polling forever.
+            if data is None:
+                err = preplanner.get_plan_error(filename) or 'Plan failed'
+                self.write_json(dict(progress = 1, error = err))
+                return
             meta, positions, speeds = data
 
             if dataType == '/positions': data = positions