Fix same preview-not-updating bug in PrusaLink and OctoPrint handlers

Same root cause as the Klipper fix: the job-preview channel was only
pushed a state the moment the file/thumbnail reference changed, so an
item linked afterward never received a value until the next print job.
Cache the last fetched thumbnail and re-push it every refresh cycle.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Signed-off-by: Scott Hanson <scooter_seh@yahoo.com>

Author: computergeek1507

bundles/org.openhab.binding.threedprinter/src/main/java/org/openhab/binding/threedprinter/internal/handler/OctoPrintHandler.java

@@ -57,6 +57,7 @@ public class OctoPrintHandler extends AbstractPrinterHandler {
 
     private @Nullable OctoPrintConfiguration config;
     private String lastPreviewFilename = "";
+    private @Nullable RawType lastPreviewState;
 
     public OctoPrintHandler(Thing thing, HttpClient httpClient) {
         super(thing, httpClient);
@@ -164,12 +165,22 @@ protected void refresh() {
                         byte @Nullable [] bytes = httpGetBytes(
                                 baseUrl + "/plugin/prusaslicerthumbnails/thumbnail/" + encodedName, cfg.apiKey);
                         if (bytes != null && bytes.length > 0) {
-                            updateState(CHANNEL_JOB_PREVIEW, new RawType(bytes, "image/png"));
+                            RawType state = new RawType(bytes, "image/png");
+                            updateState(CHANNEL_JOB_PREVIEW, state);
                             lastPreviewFilename = filename;
+                            lastPreviewState = state;
+                        }
+                    } else {
+                        // Re-push the cached image every cycle rather than only on change, so a channel
+                        // linked to an item after the initial fetch (or a UI reconnecting) still gets it.
+                        RawType cached = lastPreviewState;
+                        if (cached != null) {
+                            updateState(CHANNEL_JOB_PREVIEW, cached);
                         }
                     }
                 } else {
                     lastPreviewFilename = "";
+                    lastPreviewState = null;
                 }
             }
         }

bundles/org.openhab.binding.threedprinter/src/main/java/org/openhab/binding/threedprinter/internal/handler/PrusaLinkHandler.java

@@ -53,6 +53,7 @@ public class PrusaLinkHandler extends AbstractPrinterHandler {
 
     private @Nullable PrusaLinkConfiguration config;
     private String lastPreviewFilename = "";
+    private @Nullable RawType lastPreviewState;
 
     public PrusaLinkHandler(Thing thing, HttpClient httpClient) {
         super(thing, httpClient);
@@ -139,20 +140,32 @@ private void updateJobFile(String baseUrl, String apiKey) {
         if (file == null) {
             updateState(CHANNEL_JOB_NAME, new StringType(""));
             lastPreviewFilename = "";
+            lastPreviewState = null;
             return;
         }
 
         String name = file.displayName.isBlank() ? file.name : file.displayName;
         updateState(CHANNEL_JOB_NAME, new StringType(name));
 
         String thumbnailRef = file.refs != null ? file.refs.thumbnail : "";
-        if (thumbnailRef.isBlank() || thumbnailRef.equals(lastPreviewFilename)) {
+        if (thumbnailRef.isBlank()) {
+            return;
+        }
+        if (thumbnailRef.equals(lastPreviewFilename)) {
+            // Re-push the cached image every cycle rather than only on change, so a channel linked to an
+            // item after the initial fetch (or a UI reconnecting) still gets the preview.
+            RawType cached = lastPreviewState;
+            if (cached != null) {
+                updateState(CHANNEL_JOB_PREVIEW, cached);
+            }
             return;
         }
         byte[] bytes = httpGetBytes(baseUrl + thumbnailRef, apiKey);
         if (bytes != null && bytes.length > 0) {
-            updateState(CHANNEL_JOB_PREVIEW, new RawType(bytes, "image/png"));
+            RawType state = new RawType(bytes, "image/png");
+            updateState(CHANNEL_JOB_PREVIEW, state);
             lastPreviewFilename = thumbnailRef;
+            lastPreviewState = state;
         }
     }