refactor(vom): preserve complete canvas candidates with exact deduplication

apps/extension/src/tools/vom/visual-dedup.ts

@@ -0,0 +1,64 @@
+import { createCaptureCheckpoint } from "./capture-abort";
+import type { VisualCandidate, VisualDiscoveryResult } from "./visual-discovery";
+
+export const MAX_VISUAL_DEDUP_KEYS = 50_000;
+
+export interface VisualDedupResult extends VisualDiscoveryResult {
+  /** Known valid candidates in this capture, not the total Canvas count on the page. */
+  readonly candidateCount: number;
+  /** Candidates actually removed by exact coverage deduplication. */
+  readonly deduplicatedCount: number;
+  readonly dedupDegraded: boolean;
+}
+
+/** Keep the first real anchor for each exact DOM/parent/crop key, in encounter order.
+ * Once the key set is full, unknown keys pass through: capacity never drops candidates. */
+export async function deduplicateVisualCandidates(
+  discovery: VisualDiscoveryResult,
+  signal?: AbortSignal,
+): Promise<VisualDedupResult> {
+  const checkpoint = createCaptureCheckpoint(signal);
+  const keys = new Set<string>();
+  const candidates: VisualCandidate[] = [];
+  let deduplicatedCount = 0;
+  let dedupDegraded = false;
+  for (let i = 0; i < discovery.candidates.length; i++) {
+    if (i % 256 === 0) {
+      const pending = checkpoint();
+      if (pending) await pending;
+    }
+    const candidate = discovery.candidates[i];
+    const {
+      document,
+      region: { crop },
+    } = candidate;
+    const key = JSON.stringify([
+      document.attachmentId,
+      document.target.tabId,
+      document.target.sessionId ?? null,
+      document.frameId,
+      document.documentElementBackendNodeId,
+      candidate.parentBackendNodeId,
+      crop.x,
+      crop.y,
+      crop.width,
+      crop.height,
+    ]);
+    if (keys.has(key)) {
+      deduplicatedCount++;
+      continue;
+    }
+    if (keys.size < MAX_VISUAL_DEDUP_KEYS) keys.add(key);
+    else dedupDegraded = true;
+    candidates.push(candidate);
+  }
+  const pending = checkpoint();
+  if (pending) await pending;
+  return {
+    ...discovery,
+    candidates,
+    candidateCount: discovery.candidates.length,
+    deduplicatedCount,
+    dedupDegraded,
+  };
+}