Summary popover: real blur under the glass in see-through windows

webviews/src/agent-session/acpmux/chatUnderGlass.ts

@@ -0,0 +1,22 @@
+// What a glass floating over the chat covers, for its in-place blur (ui/glass/seeThroughBlur.ts):
+// the chat stage's own blocks (its header, the transcript, a strip or a panel in it), never a whole
+// column. The Summary popover sits in the stage and Session Info beside the chat's column
+// (.acpmux-main), so a column-wide filter would also take the composer and make the column one
+// stacking context; the stage's blocks are only what is under the glass. The surfaces themselves are
+// skipped by seeThroughBlur.
+import type { CoveredCandidates, SeeThroughOptions } from "../../ui/glass/seeThroughBlur";
+
+export const chatUnderGlass: CoveredCandidates = (surface) =>
+  surface.closest(".acpmux-shell")?.querySelectorAll(".acpmux-stage > *") ?? [];
+
+// The composer never takes a filter (it would re-anchor the composer's fixed menus), so a glass over
+// it keeps its underlay there: a short pane's Session Info reaches down over the composer.
+const composer: CoveredCandidates = (surface) =>
+  surface.closest(".acpmux-shell")?.querySelectorAll(".acpmux-dock") ?? [];
+
+/** Session Info's overlay. */
+export const chatGlass: SeeThroughOptions = { keepUnderlayOver: composer };
+
+/** The Summary popover: its blocks carry data-glass-under="summary", which summary.css switches off
+ * while it hides the card (Find, review, inspect), with no observer to see that happen. */
+export const summaryGlass: SeeThroughOptions = { owner: "summary", keepUnderlayOver: composer };

webviews/src/agent-session/acpmux/session-info/SessionInfo.tsx

@@ -44,6 +44,8 @@ import {
   type ReactNode,
 } from "react";
 import { flushSync } from "react-dom";
+import { useSeeThroughBlur } from "../../../ui/glass/seeThroughBlur";
+import { chatGlass, chatUnderGlass } from "../chatUnderGlass";
 import { usePresence, type Presence } from "../../../ui/presence";
 import { useChatDisplay } from "../chatDisplay";
 import { CHAT_LAYOUT_EVENT, chatColumnOf, useChatSizing, type ChatColumn } from "../chatWidth";
@@ -861,6 +863,11 @@ export function SessionInfoPanel({
   const t = useT();
   const frame = useRef<HTMLElement | null>(null);
   const drag = useRef<{ right: number } | undefined>(undefined);
+  // Floating over the chat (the narrow pane's Summary popover), the chat under it blurs itself there in
+  // a see-through Chromium page (ui/glass/seeThroughBlur.ts), as WebKit's backdrop draws it, so its
+  // text never reads through the glass (Leo 2026-10-30: "I don't like the non-glassness"). Pushing,
+  // it sits beside the chat and covers nothing.
+  useSeeThroughBlur(frame, placement === "overlay", chatUnderGlass, chatGlass);
   // The foot animates only once it has been drawn at its first measure: the open draws it at once.
   const footKnown = foot !== undefined && foot > 0;
   const [footSettled, setFootSettled] = useState(false);

webviews/src/agent-session/acpmux/summary/SummaryCard.tsx

@@ -1,6 +1,8 @@
 import React, { useEffect, useMemo, useRef, useState } from "react";
 import { flushSync } from "react-dom";
 import { useEscapeCloses } from "../../../ui/escapeDismiss";
+import { useSeeThroughBlur } from "../../../ui/glass/seeThroughBlur";
+import { chatUnderGlass, summaryGlass } from "../chatUnderGlass";
 import { usePresence } from "../../../ui/presence";
 import { useT } from "../i18n";
 import { Icon } from "../icons/Icon";
@@ -141,6 +143,11 @@ export function SummaryCard({
     [shown, registry.processes, registry.listed, summary, running],
   );
   const panel = useRef<HTMLElement>(null);
+  // The popover floats over the chat: in a see-through Chromium page the chat under it blurs itself
+  // there (ui/glass/seeThroughBlur.ts), as WebKit's backdrop draws it, so its text never reads
+  // through the glass (Leo 2026-10-30: "I don't like the non-glassness"). The inline column is
+  // beside the chat and covers nothing.
+  useSeeThroughBlur(panel, drawn && !card.column, chatUnderGlass, summaryGlass);
   const popover = shown && !card.column;
   const edges = useScrollEdges();
   const close = card.close;

webviews/src/ui/glass/glass.css

@@ -142,7 +142,8 @@
    page's flow (a user's bubble, a settings card) has nothing under it and keeps its tint, as in
    WebKit. WebKit (which keeps -webkit-backdrop-filter), an opaque window and the lens (whose canvas
    is under the glass) keep the tint alone. The strength is the experiment chromium-glass-underlay
-   (chromiumUnderlay.experiment.ts, which desktop.ts puts on <html>). */
+   (chromiumUnderlay.experiment.ts, which desktop.ts puts on <html>). A surface whose page blurs
+   itself under it (seeThroughBlur.ts, below) needs no underlay and draws none. */
 :root {
   --glass-underlay: 70%;
 }
@@ -163,6 +164,18 @@
         linear-gradient(var(--glass-tint), var(--glass-tint)),
         color-mix(in srgb, var(--glass-surface) var(--glass-underlay), transparent);
     }
+    /* THE PAGE BLURS ITSELF UNDER THE GLASS (Leo 2026-10-30, on the Summary popover: "I don't like
+       the non-glassness"). A surface that uses seeThroughBlur.ts (data-glass-over) makes what it
+       covers blur its own pixels inside the surface's rounded rect: each covered element
+       (data-glass-under) draws through its own SVG filter. The text under the glass is then
+       blurred in place, as WebKit's backdrop draws it, so the surface needs no underlay to hide it:
+       its tint and that blur carry the legibility (design/overlay-surfaces.md). */
+    :root[data-cmux-see-through]:not([data-glass-lens], [data-reduce-transparency]) [data-glass-under] {
+      filter: var(--glass-under-filter);
+    }
+    :root[data-cmux-see-through]:not([data-glass-lens], [data-reduce-transparency]) .ui-glass[data-glass-over] {
+      --glass-underlay: 0%;
+    }
   }
 }