feat(ui): highlight external SSE annotations inline on plan text

packages/editor/App.tsx

@@ -53,6 +53,7 @@ import { useAnnotationDraft } from '@plannotator/ui/hooks/useAnnotationDraft';
 import { useArchive } from '@plannotator/ui/hooks/useArchive';
 import { useEditorAnnotations } from '@plannotator/ui/hooks/useEditorAnnotations';
 import { useExternalAnnotations } from '@plannotator/ui/hooks/useExternalAnnotations';
+import { useExternalAnnotationHighlights } from '@plannotator/ui/hooks/useExternalAnnotationHighlights';
 import { useFileBrowser } from '@plannotator/ui/hooks/useFileBrowser';
 import { isVaultBrowserEnabled } from '@plannotator/ui/utils/obsidian';
 import { isFileBrowserEnabled, getFileBrowserSettings } from '@plannotator/ui/utils/fileBrowser';
@@ -386,6 +387,16 @@ const App: React.FC = () => {
   const { editorAnnotations, deleteEditorAnnotation } = useEditorAnnotations();
   const { externalAnnotations, updateExternalAnnotation, deleteExternalAnnotation } = useExternalAnnotations<Annotation>({ enabled: isApiMode });
 
+  // Drive DOM highlights for SSE-delivered external annotations. Disabled
+  // while a linked doc overlay is open (Viewer DOM is hidden) and while the
+  // plan diff view is active (diff view has its own annotation surface).
+  const { reset: resetExternalHighlights } = useExternalAnnotationHighlights({
+    viewerRef,
+    externalAnnotations,
+    enabled: isApiMode && !linkedDocHook.isActive && !isPlanDiffActive,
+    planKey: markdown,
+  });
+
   // Merge local + SSE annotations, deduping draft-restored externals against
   // live SSE versions. Prefer the SSE version when both exist (same source,
   // type, and originalText). This avoids the timing issues of an effect-based
@@ -473,10 +484,13 @@ const App: React.FC = () => {
         viewerRef.current?.clearAllHighlights();
         viewerRef.current?.applySharedAnnotations(pendingSharedAnnotations.filter(a => !a.diffContext));
         clearPendingSharedAnnotations();
+        // `clearAllHighlights` wiped live external SSE highlights too;
+        // tell the external-highlight bookkeeper to re-apply them.
+        resetExternalHighlights();
       }, 100);
       return () => clearTimeout(timer);
     }
-  }, [pendingSharedAnnotations, clearPendingSharedAnnotations]);
+  }, [pendingSharedAnnotations, clearPendingSharedAnnotations, resetExternalHighlights]);
 
   const handleTaterModeChange = (enabled: boolean) => {
     setTaterMode(enabled);

packages/ui/hooks/useExternalAnnotationHighlights.ts

@@ -0,0 +1,105 @@
+import { useCallback, useEffect, useRef, useState } from 'react';
+import type { Annotation } from '../types';
+import { AnnotationType } from '../types';
+import type { ViewerHandle } from '../components/Viewer';
+
+/**
+ * Bridges SSE-delivered external annotations into the Viewer's imperative
+ * highlight API so tools can POST annotations with `originalText` and have
+ * them highlight real spans of the rendered plan.
+ *
+ * The Viewer's `applySharedAnnotations` already searches the DOM for
+ * `originalText` and dedupes against already-applied marks, so this hook
+ * just needs to drive it when the external list changes.
+ *
+ * - Annotations without `originalText` (or `GLOBAL_COMMENT`) stay sidebar-only.
+ * - Annotations with `diffContext` are skipped (diff view owns those).
+ * - On plan markdown change the applied set is cleared so re-rendered blocks
+ *   get re-highlighted.
+ * - Callers can invoke the returned `reset()` to force a full re-apply — used
+ *   by the share-import path in App.tsx after it calls `clearAllHighlights()`,
+ *   which would otherwise leave our bookkeeping stale against a wiped DOM.
+ * - Disabled state no-ops WITHOUT clearing the applied set. This preserves the
+ *   bookkeeping while the Viewer DOM is hidden (diff view / linked doc) so that
+ *   any SSE removals that arrive while hidden are correctly reconciled when the
+ *   hook re-enables.
+ */
+export function useExternalAnnotationHighlights(params: {
+  viewerRef: React.RefObject<ViewerHandle | null>;
+  externalAnnotations: Annotation[];
+  enabled: boolean;
+  /** Bump to force a full re-apply (e.g. plan markdown changed and blocks re-rendered). */
+  planKey: string;
+}): { reset: () => void } {
+  const { viewerRef, externalAnnotations, enabled, planKey } = params;
+
+  // Tracks annotation IDs currently materialized as DOM highlights, along
+  // with a fingerprint so updates trigger remove+reapply.
+  const appliedRef = useRef<Map<string, string>>(new Map());
+
+  // Bumped to force the main effect to treat every current external as a
+  // fresh application target — used by `reset()` below.
+  const [resetCount, setResetCount] = useState(0);
+
+  // Clear tracking when plan content changes — the Viewer re-parses blocks
+  // and wipes marks, so our bookkeeping is stale.
+  useEffect(() => {
+    appliedRef.current.clear();
+  }, [planKey]);
+
+  useEffect(() => {
+    if (!enabled) return;
+
+    const viewer = viewerRef.current;
+    if (!viewer) return;
+
+    const eligible = externalAnnotations.filter(
+      a => a.type !== AnnotationType.GLOBAL_COMMENT && !a.diffContext && a.originalText,
+    );
+    const applied = appliedRef.current;
+
+    // Removals: previously applied but no longer present, or fingerprint changed.
+    const toRemove: string[] = [];
+    for (const [id, fp] of applied) {
+      const match = eligible.find(a => a.id === id);
+      if (!match || fingerprint(match) !== fp) {
+        toRemove.push(id);
+      }
+    }
+    toRemove.forEach(id => {
+      viewer.removeHighlight(id);
+      applied.delete(id);
+    });
+
+    // Additions: eligible but not yet applied (includes re-adds from updates).
+    const toAdd = eligible.filter(a => !applied.has(a.id));
+    if (toAdd.length === 0) return;
+
+    // Paint delay matches the existing draft/share restore pattern —
+    // ensures blocks are mounted before we walk the DOM.
+    const timer = setTimeout(() => {
+      const v = viewerRef.current;
+      if (!v) return;
+      v.applySharedAnnotations(toAdd);
+      toAdd.forEach(a => applied.set(a.id, fingerprint(a)));
+    }, 100);
+
+    return () => clearTimeout(timer);
+    // viewerRef is a stable ref object and intentionally omitted from deps.
+  }, [externalAnnotations, enabled, planKey, resetCount]);
+
+  // Forget everything we've tracked and force a full re-apply on the next
+  // effect run. Callers invoke this after an external action has wiped the
+  // Viewer DOM out from under us (e.g. `clearAllHighlights()` during share
+  // import) so live externals get repainted.
+  const reset = useCallback(() => {
+    appliedRef.current.clear();
+    setResetCount(c => c + 1);
+  }, []);
+
+  return { reset };
+}
+
+function fingerprint(a: Annotation): string {
+  return `${a.type}\u0000${a.originalText}`;
+}