fix: limit resource preview watches to active tab

Root cause: every local resource preview tab kept its own /api/local-folder/events EventSource alive. Hidden PDF and Office tabs consumed browser same-origin connection slots, so later preview iframes/file reads stalled and rendered as blank pages.

Changes:
- keep passive resource file watching active-tab only
- close inactive resource-tab EventSources on tab activation and release
- update the bug record with the PDF fifth-open and XLSX fourth-open repro and verification

Verification:
- node --check rust/crates/mnote-web/browser/document-resource-tab-runtime.js
- cargo test -p mnote-web --manifest-path rust/Cargo.toml pdf_preview_page_does_not_render_visible_toolbar
- cargo test -p mnote-web --manifest-path rust/Cargo.toml document_shell_returns_page_aggregate_snapshot
- cargo build -p mnote-web --manifest-path rust/Cargo.toml
- browser smoke: opened 5 XLSX previews; #4 and #5 completed with tableCount=1
- browser smoke: opened 5 DHA PDFs; #5 rendered 8/8 canvases, iframeCount=0, browser errors=0

rust/crates/mnote-web/browser/document-resource-tab-runtime.js

@@ -708,6 +708,7 @@ export const createResourceTabRuntime = (dependencies = {}) => {
     if (!activeEntry && window.__mnoteIntendedSlashRoot instanceof HTMLElement) window.__mnoteIntendedSlashRoot = null;
     if (role === 'primary') syncActiveResourceFileTreeRow(activeResource);
     syncActiveResourceUrlState(activeResource, role);
+    syncActivePassiveResourceWatch(role, activeResource);
     syncOpenEditorsSnapshot();
   };
 
@@ -898,12 +899,7 @@ export const createResourceTabRuntime = (dependencies = {}) => {
       }
       entry.mindmapRuntime = null;
     }
-    if (entry.resourceWatchEventSource) {
-      try {
-        entry.resourceWatchEventSource.close();
-      } catch (_) {}
-      entry.resourceWatchEventSource = null;
-    }
+    closePassiveResourceWatch(entry);
     if (entry.panel instanceof HTMLElement) entry.panel.replaceChildren();
   };
 
@@ -1092,11 +1088,40 @@ export const createResourceTabRuntime = (dependencies = {}) => {
     }
   };
 
+  const closePassiveResourceWatch = (entry) => {
+    if (!entry?.resourceWatchEventSource) return;
+    try {
+      entry.resourceWatchEventSource.close();
+    } catch (_) {}
+    entry.resourceWatchEventSource = null;
+    if (entry.panel instanceof HTMLElement) entry.panel.removeAttribute('data-mnote-resource-watch-ready');
+  };
+
+  const isActiveResourceTabEntry = (entry) => {
+    if (!(entry?.panel instanceof HTMLElement)) return false;
+    if (entry.panel.hidden === false) return true;
+    return entry.tab instanceof HTMLElement && entry.tab.getAttribute('aria-selected') === 'true';
+  };
+
+  const closeInactivePassiveResourceWatches = (activeEntry) => {
+    const role = normalizePaneRole(activeEntry?.paneRole || 'primary');
+    resourceTabRegistry.forEach((entry) => {
+      if (entry === activeEntry) return;
+      if (normalizePaneRole(entry?.paneRole) !== role) return;
+      closePassiveResourceWatch(entry);
+    });
+  };
+
   const installPassiveResourceWatch = (entry) => {
     if (!entry || entry.session || typeof window.EventSource !== 'function') return;
     const rootUri = String(entry.rootUri || '').trim();
     const path = String(entry.path || '').trim();
     if (!rootUri || !path) return;
+    if (!isActiveResourceTabEntry(entry)) {
+      closePassiveResourceWatch(entry);
+      return;
+    }
+    closeInactivePassiveResourceWatches(entry);
     if (entry.resourceWatchEventSource) {
       try {
         entry.resourceWatchEventSource.close();
@@ -1130,6 +1155,17 @@ export const createResourceTabRuntime = (dependencies = {}) => {
     });
   };
 
+  const syncActivePassiveResourceWatch = (paneRole, activeResource) => {
+    const activeEntry = activeResource ? resourceTabRegistry.get(activeResource) : null;
+    if (!activeEntry) {
+      resourceTabRegistry.forEach((entry) => {
+        if (normalizePaneRole(entry?.paneRole) === normalizePaneRole(paneRole)) closePassiveResourceWatch(entry);
+      });
+      return;
+    }
+    installPassiveResourceWatch(activeEntry);
+  };
+
   const releaseInlinePdfResource = (entry) => {
     if (!entry) return;
     const pdf = entry.inlinePdfDocument;