perf(vom): make active hover probing opt-in on observe

Every tool.observe moved the real cursor across the page to look for
hover-only menus and tooltips. Measured against real Chrome, that cost a
median of 2.5s and up to 4.7s per observation — 73% to 99% of total
observe wall clock — and returned 3 hits across 12 pages. A positive
control confirms the probes work; the yield on real pages simply does not
justify putting them on the default path.

observe now probes only when asked, via `probe_hover` (`--probe-hover`).
Agents that know which element hides a menu should keep using
`bsk hover <ref>`, which is both cheaper and precise. A held hover latch
still suppresses probing, since probing would move the cursor off the
element the caller is deliberately holding.

Correctness fixes that apply whether or not probing is requested:

- Hover probing ran between the DOM snapshot and the accessibility tree
  fetch, so a hover that opened a menu left one half of an observation
  describing the page before the change and the other half after it. Both
  chains now run after all capture is complete.
- The overlay bypass toggled once per chain and swallowed restore
  failures, which could leave the agent overlay hidden for the rest of
  the tab's life. It is now reference counted across both chains, and a
  failed restore is reported instead of discarded.
- Observations report whether they hovered the page and whether that
  revealed content the static tree lacks, so callers can judge how far
  the live page may have drifted from the returned snapshot.

Probe budgets were checked at the top of the loop, so a candidate could
start with 1ms remaining and still run a full settle window, overshooting
by up to 634ms. Candidates are now admitted only if they fit. Raising
MAX_HOVER_PROBE_MS to 2600 is part of that fix rather than a relaxation:
2000 was never the real ceiling, and enforcing it literally would have
silently dropped a candidate the positive control depends on.

Tooltip misses are cached too, with a shorter TTL than hits, so repeat
observations of the same page no longer re-probe every unlabelled control
from scratch.

apps/extension/src/tools/observation.ts

@@ -49,11 +49,14 @@ import {
 import { resolveSnapshotRef } from "./snapshot-ref";
 import {
   type CapturedNode,
+  type CapturedSurfaceProbe,
   type CapturedViewModel,
   captureViewModel,
   collectOverlayExcludedBackendIds,
+  probeHoverSurfaces,
 } from "./vom/capture";
 import { type CapturedFrameDocument, captureFrameData } from "./vom/frame-capture";
+import { withOverlayBypass } from "./vom/hover-perception";
 import { probeTooltipNames } from "./vom/name-enrichment";
 import {
   type CaptureVomObservationResult,
@@ -525,8 +528,11 @@ function buildActiveScopeBlocks(nodes: VomNode[], signals: VomNodeDomSignals): A
   return blocks;
 }
 
-function buildConditionalSurfaces(nodes: VomNode[], captured: CapturedViewModel): CondSurface[] {
-  const probes = captured.surfaceProbes ?? [];
+function buildConditionalSurfaces(
+  nodes: VomNode[],
+  captured: CapturedViewModel,
+  probes: CapturedSurfaceProbe[],
+): CondSurface[] {
   if (probes.length === 0) return [];
 
   const surfaces: CondSurface[] = [];
@@ -649,6 +655,7 @@ function findSurfaceNodeByPoint(
 export interface BuildVomSceneOptions {
   pageUrl?: string;
   supplementalNames?: ReadonlyMap<string, string>;
+  surfaceProbes?: CapturedSurfaceProbe[];
 }
 
 export type VomFrameDocument = CapturedFrameDocument<CdpAxNode>;
@@ -817,18 +824,19 @@ export function buildFrameVomScene(
     excludedBackendNodeIds: captured.excludedBackendNodeIds,
     supplementalNames: options.supplementalNames,
   });
-  return attachCapturedSceneAnnotations(scene, documents, captured);
+  return attachCapturedSceneAnnotations(scene, documents, captured, options.surfaceProbes ?? []);
 }
 
 function attachCapturedSceneAnnotations(
   scene: VomScene,
   documents: VomFrameDocument[],
   captured: CapturedViewModel,
+  surfaceProbes: CapturedSurfaceProbe[],
 ): VomScene {
   const rootDocument = documents.find((document) => document.frameId === scene.rootFrameId);
   const signals = capturedOnlySignals(rootDocument?.domNodes ?? captured.nodes);
   const activeScopeBlocks = buildActiveScopeBlocks(scene.nodes, signals);
-  const surfaces = buildConditionalSurfaces(scene.nodes, captured);
+  const surfaces = buildConditionalSurfaces(scene.nodes, captured, surfaceProbes);
   return {
     ...scene,
     ...(surfaces.length > 0 ? { surfaces } : {}),
@@ -1010,17 +1018,69 @@ async function captureForVom(
   options: CaptureVomObservationOptions,
 ): Promise<CapturedViewModel> {
   try {
-    return await captureViewModel(cdp, tabId, {
-      conditionalSurfaceProbe: options.conditionalSurfaceProbe ?? false,
-      hoverProbeBypassOverlay: options.hoverProbeBypassOverlay,
-      signal: options.signal,
-    });
+    return await captureViewModel(cdp, tabId, { signal: options.signal });
   } catch (error) {
     if (isAbortError(error)) throw error;
     return fallbackCapturedViewModel(cdp, tabId, options.signal);
   }
 }
 
+export interface HoverProbeOutcome {
+  /** Whether any active hover was dispatched during this observation. */
+  performed: boolean;
+  /**
+   * Whether hovering surfaced content absent from the static snapshot. Cached
+   * tooltip names count, so this may over-report on repeat observations — it
+   * errs towards telling the caller the snapshot is less fresh than it looks.
+   */
+  revealedContent: boolean;
+  surfaceProbes: CapturedSurfaceProbe[];
+  tooltipNames: Map<string, string>;
+}
+
+const NO_HOVER_PROBES: HoverProbeOutcome = {
+  performed: false,
+  revealedContent: false,
+  surfaceProbes: [],
+  tooltipNames: new Map(),
+};
+
+/**
+ * Runs both active-hover chains back to back.
+ *
+ * Ordering matters: this happens after DOM *and* accessibility capture so a
+ * hover that opens a menu cannot leave one half of the observation describing
+ * the page before the change and the other half after it. Sharing one overlay
+ * bypass span also means the agent overlay toggles once per observation
+ * instead of once per chain.
+ */
+async function runHoverProbes(
+  cdp: CdpRunner,
+  tabId: number,
+  captured: CapturedViewModel,
+  documents: VomFrameDocument[],
+  staticSemantics: ReturnType<typeof resolveSemanticGraph>,
+  options: CaptureVomObservationOptions,
+): Promise<HoverProbeOutcome> {
+  if (!options.conditionalSurfaceProbe) return NO_HOVER_PROBES;
+
+  return withOverlayBypass(options.hoverProbeBypassOverlay, tabId, async () => {
+    const surfaceProbes = await probeHoverSurfaces(cdp, tabId, captured.nodes, {
+      signal: options.signal,
+    });
+    throwIfAborted(options.signal, "observation");
+    const tooltipNames = await probeTooltipNames(cdp, tabId, documents, staticSemantics, {
+      signal: options.signal,
+    });
+    return {
+      performed: true,
+      revealedContent: surfaceProbes.length > 0 || tooltipNames.size > 0,
+      surfaceProbes,
+      tooltipNames,
+    };
+  });
+}
+
 export interface CaptureVomObservationOptions extends VomOptions {
   conditionalSurfaceProbe?: boolean;
   hoverProbeBypassOverlay?: (tabId: number, enabled: boolean) => Promise<void>;
@@ -1051,19 +1111,26 @@ export async function captureVomObservation(
     excludedBackendNodeIds: captured.excludedBackendNodeIds,
   });
   const staticSemantics = resolveSemanticGraph(semanticGraph, { identifierFallback: false });
-  const tooltipNames = options.conditionalSurfaceProbe
-    ? await probeTooltipNames(cdp, tabId, normalizedDocuments, staticSemantics, {
-        signal: options.signal,
-        hoverProbeBypassOverlay: options.hoverProbeBypassOverlay,
-      })
-    : new Map<string, string>();
+  const hoverProbes = await runHoverProbes(
+    cdp,
+    tabId,
+    captured,
+    normalizedDocuments,
+    staticSemantics,
+    options,
+  );
   throwIfAborted(options.signal, "observation");
   const scene = projectSemanticGraph(
     normalizeSemanticStructure(
-      resolveSemanticGraph(semanticGraph, { supplementalNames: tooltipNames }),
+      resolveSemanticGraph(semanticGraph, { supplementalNames: hoverProbes.tooltipNames }),
     ),
   );
-  const decoratedScene = attachCapturedSceneAnnotations(scene, normalizedDocuments, captured);
+  const decoratedScene = attachCapturedSceneAnnotations(
+    scene,
+    normalizedDocuments,
+    captured,
+    hoverProbes.surfaceProbes,
+  );
   const rendered = renderVom(decoratedScene, {
     maxDepth: options.maxDepth,
     maxTokens: options.maxTokens,
@@ -1075,7 +1142,11 @@ export async function captureVomObservation(
     rootFrameId: captured.rootFrameId ?? normalizedDocuments[0]?.frameId ?? "root",
     frameDocuments: normalizedDocuments,
     rendered,
-    surfaceProbes: captured.surfaceProbes,
+    surfaceProbes: hoverProbes.surfaceProbes,
+    hoverProbe: {
+      performed: hoverProbes.performed,
+      revealedContent: hoverProbes.revealedContent,
+    },
   });
 }
 
@@ -1141,6 +1212,14 @@ async function handleVomObservation(
       ref_count: observation.refs.length,
       tab_id: target.tabId,
       truncated: observation.truncated,
+      ...(toolName === "observe" && observation.hoverProbe?.performed
+        ? {
+            hover_probe: {
+              performed: true,
+              revealed_content: observation.hoverProbe.revealedContent,
+            },
+          }
+        : {}),
       ...(toolName === "observe" && (params as ObserveParams).debug_surfaces
         ? {
             debug: {
@@ -1179,5 +1258,13 @@ export async function handleObserve(
   deps: SnapshotDeps = getDefaultDeps(),
   signal?: AbortSignal,
 ): Promise<ObserveResult | RpcError> {
-  return handleVomObservation(manager, params, "observe", "transient_input", true, deps, signal);
+  return handleVomObservation(
+    manager,
+    params,
+    "observe",
+    "transient_input",
+    params.probe_hover === true,
+    deps,
+    signal,
+  );
 }