fix(channels): collapse overflowing tag suggestions into a "+N" pill

With 2+ suggestions the narrow tags cell clipped the second ghost chip
mid-word right next to the edit "+", reading as the icon covering it. Route
the ghost chips through the same fit machinery the attached chips use: a
dedicated SuggestedChipsLane fits what the cell holds and collapses the rest
into a "+N" pill whose hover popover still one-tap accepts / dismisses each.

The lane is attached-XOR-ghost (suggestions are untagged-only, and accepting
one now drops the whole channel from the suggestion cache), so each lane owns
the full cell width instead of clipping the other.

frontend/src/components/ChannelTags.suggest.dom.test.tsx

@@ -11,9 +11,13 @@ import { FloatingTree } from "@floating-ui/react";
 
 vi.mock("react-i18next", async (importOriginal) => {
   const actual = await importOriginal<typeof import("react-i18next")>();
+  // Interpolate the `name` option so per-tag accept labels are distinguishable ("…acceptSuggestion:docu").
   return {
     ...actual,
-    useTranslation: () => ({ t: (key: string) => key, i18n: { language: "en" } }),
+    useTranslation: () => ({
+      t: (key: string, opts?: { name?: string }) => (opts?.name ? `${key}:${opts.name}` : key),
+      i18n: { language: "en" },
+    }),
   };
 });
 
@@ -72,8 +76,8 @@ function renderControl(props: Partial<Parameters<typeof ChannelTagsControl>[0]>
 describe("ChannelTagsControl suggested ghost chips", () => {
   it("renders a ghost chip per suggestion and accepts on click", () => {
     const { onAccept } = renderControl();
-    // Both suggested tag names show (attached row is empty on an untagged channel).
-    fireEvent.click(screen.getByText("docu"));
+    // Role query excludes the aria-hidden fit-measurer copy; the name carries the interpolated tag.
+    fireEvent.click(screen.getByRole("button", { name: "channels.tags.acceptSuggestion:docu" }));
     expect(onAccept).toHaveBeenCalledWith(docu.id);
   });
 
@@ -82,19 +86,20 @@ describe("ChannelTagsControl suggested ghost chips", () => {
     const dismissButtons = screen.getAllByRole("button", {
       name: "channels.tags.dismissSuggestion",
     });
-    // Order matches the suggestions array — the second × is the "history" suggestion.
+    // Two visible ghost chips (the measurer's copies are aria-hidden → excluded); order matches the
+    // suggestions array, so the second × is the "history" suggestion.
+    expect(dismissButtons).toHaveLength(2);
     fireEvent.click(dismissButtons[1]!);
     expect(onDismiss).toHaveBeenCalledWith(history.id);
     expect(onAccept).not.toHaveBeenCalled();
   });
 
-  it("never shows a suggestion whose tag the channel already carries", () => {
+  it("shows the attached lane (no ghost chips) once the channel carries a user tag", () => {
     renderControl({ attachedIds: [docu.id] });
-    // docu is attached → its ghost chip is suppressed (only history's × remains). Counting the
-    // dismiss buttons avoids colliding with docu's now-present *attached* chip text.
-    const dismissButtons = screen.getAllByRole("button", {
-      name: "channels.tags.dismissSuggestion",
-    });
-    expect(dismissButtons).toHaveLength(1);
+    // A tagged channel is not "untagged" → the ghost lane is not rendered at all (the server excludes
+    // tagged channels from suggestions; the control mirrors that with its attached-XOR-ghost branch).
+    expect(
+      screen.queryAllByRole("button", { name: "channels.tags.dismissSuggestion" }),
+    ).toHaveLength(0);
   });
 });

frontend/src/components/ChannelTags.tsx

@@ -85,6 +85,110 @@ function SuggestedChip({
   );
 }
 
+const GHOST_PILL =
+  "shrink-0 text-3xs px-1.5 py-0.5 rounded-full border border-dashed border-accent/50 text-accent/90";
+
+/** A single-line lane of suggested ghost chips that collapses its overflow into a "+N" pill (hover
+ *  reveals the rest, still accept/dismiss-able), reusing the SAME fit machinery as the attached-chip
+ *  lane. Rendered in the untagged-channel case only, so it owns the full tags-cell width — this is what
+ *  stops a 2nd suggestion from being clipped mid-word right next to the edit "+". */
+function SuggestedChipsLane({
+  suggestions,
+  onAccept,
+  onDismiss,
+}: {
+  suggestions: SuggestedTag[];
+  onAccept: (tagId: number) => void;
+  onDismiss: (tagId: number) => void;
+}) {
+  const rowRef = useRef<HTMLDivElement | null>(null);
+  const chipRefs = useRef<Array<HTMLElement | null>>([]);
+  const pillRef = useRef<HTMLSpanElement | null>(null);
+  const key = suggestions.map((s) => `${s.tag.id}:${s.tag.name}`).join("|");
+  const visible = useChipOverflowFit<number>({
+    rowRef,
+    chipsRef: chipRefs,
+    pillRef,
+    deps: key,
+    initial: suggestions.length,
+    decide: (g) =>
+      fitChipsWithPill({ chipRights: g.chipRights, pillW: g.pillW, avail: g.avail, gap: g.gap }),
+  });
+  const hidden = suggestions.length - visible;
+
+  const [overflowOpen, setOverflowOpen] = useState(false);
+  const overflowPop = useAnchoredPopover({
+    open: overflowOpen,
+    onOpenChange: setOverflowOpen,
+    mode: "hover",
+    placement: "bottom",
+  });
+  useEffect(() => {
+    if (hidden === 0 && overflowOpen) setOverflowOpen(false);
+  }, [hidden, overflowOpen]);
+
+  return (
+    <div className="relative flex items-center gap-1 min-w-0 flex-1">
+      {/* Hidden measurer — real ghost chips at natural width so the fit hook reads their right edges. */}
+      <div
+        aria-hidden
+        className="pointer-events-none invisible absolute left-0 top-0 flex items-center gap-1 whitespace-nowrap"
+      >
+        {suggestions.map((s, i) => (
+          <span
+            key={s.tag.id}
+            ref={(el) => {
+              chipRefs.current[i] = el;
+            }}
+            className="inline-flex"
+          >
+            <SuggestedChip suggestion={s} onAccept={() => {}} onDismiss={() => {}} />
+          </span>
+        ))}
+        <span ref={pillRef} className={GHOST_PILL}>
+          +{suggestions.length}
+        </span>
+      </div>
+
+      <div ref={rowRef} className="flex items-center gap-1 min-w-0 flex-1 overflow-hidden">
+        {suggestions.slice(0, visible).map((s) => (
+          <SuggestedChip
+            key={s.tag.id}
+            suggestion={s}
+            onAccept={() => onAccept(s.tag.id)}
+            onDismiss={() => onDismiss(s.tag.id)}
+          />
+        ))}
+        {hidden > 0 && (
+          <button
+            ref={overflowPop.refs.setReference}
+            type="button"
+            className={`${GHOST_PILL} hover:text-accent transition`}
+            {...overflowPop.getReferenceProps()}
+          >
+            +{hidden}
+          </button>
+        )}
+      </div>
+
+      {/* Hover: the overflowed suggestions, each still one-tap accept / × dismiss. */}
+      <PopoverSurface
+        popover={overflowPop}
+        className="glass-menu max-w-[18rem] rounded-xl p-1.5 flex flex-wrap items-center gap-1 animate-[popIn_0.16s_ease]"
+      >
+        {suggestions.slice(visible).map((s) => (
+          <SuggestedChip
+            key={s.tag.id}
+            suggestion={s}
+            onAccept={() => onAccept(s.tag.id)}
+            onDismiss={() => onDismiss(s.tag.id)}
+          />
+        ))}
+      </PopoverSurface>
+    </div>
+  );
+}
+
 /** The editor body: toggle the user's existing tags on/off for this channel, plus an inline
  *  "create + attach" input. Rendered inside an anchored `menu` popover. (Exported for the channel
  *  detail page in Part 2; internal for now.) */
@@ -270,60 +374,65 @@ export function ChannelTagsControl({
     <div
       className={`relative flex items-center gap-1 min-w-0 ${bounded ? "w-48 max-w-full" : "w-full"}`}
     >
-      {/* Hidden measurer: all chips + a sample pill, laid out unbounded to read their true widths. Each
-          chip is wrapped in a ref span (index-aligned) so the shared fit hook can read its right edge;
-          the pill is the sample the hook reserves room for. */}
-      <div
-        aria-hidden
-        className="pointer-events-none invisible absolute left-0 top-0 flex items-center gap-1 whitespace-nowrap"
-      >
-        {attached.map((tg, i) => (
-          <span
-            key={tg.id}
-            ref={(el) => {
-              chipRefs.current[i] = el;
-            }}
-            className="inline-flex"
+      {/* Untagged + has suggestions → the ghost-chip lane (its own overflow "+N"); otherwise the
+          attached-chip lane. The two are mutually exclusive: suggestions are computed for untagged
+          channels only, and accepting one removes the channel from the suggestion set — so a channel
+          never shows both, and each lane gets the full cell width instead of clipping the other. */}
+      {attached.length === 0 && shownSuggestions.length > 0 ? (
+        <SuggestedChipsLane
+          suggestions={shownSuggestions}
+          onAccept={(tagId) => onAcceptSuggestion?.(tagId)}
+          onDismiss={(tagId) => onDismissSuggestion?.(tagId)}
+        />
+      ) : (
+        <>
+          {/* Hidden measurer: all chips + a sample pill, laid out unbounded to read their true widths.
+              Each chip is wrapped in a ref span (index-aligned) so the shared fit hook can read its
+              right edge; the pill is the sample the hook reserves room for. */}
+          <div
+            aria-hidden
+            className="pointer-events-none invisible absolute left-0 top-0 flex items-center gap-1 whitespace-nowrap"
           >
-            <TagChip tag={tg} />
-          </span>
-        ))}
-        <span ref={pillRef} className={pillClass}>
-          +{attached.length}
-        </span>
-      </div>
+            {attached.map((tg, i) => (
+              <span
+                key={tg.id}
+                ref={(el) => {
+                  chipRefs.current[i] = el;
+                }}
+                className="inline-flex"
+              >
+                <TagChip tag={tg} />
+              </span>
+            ))}
+            <span ref={pillRef} className={pillClass}>
+              +{attached.length}
+            </span>
+          </div>
 
-      <div ref={rowRef} className="flex items-center gap-1 min-w-0 flex-1 overflow-hidden">
-        {attached.slice(0, visible).map((tg) => (
-          <TagChip
-            key={tg.id}
-            tag={tg}
-            onClick={onChipClick ? () => onChipClick(tg.id, tg.name) : undefined}
-            title={onChipClick ? t("channels.row.filterFeedByTag", { name: tg.name }) : undefined}
-          />
-        ))}
-        {hidden > 0 && (
-          <button
-            ref={overflowPop.refs.setReference}
-            type="button"
-            className={`${pillClass} hover:text-fg transition`}
-            {...overflowPop.getReferenceProps()}
-          >
-            +{hidden}
-          </button>
-        )}
-        {/* Suggested ghost chips (E8·S4) ride in the same overflow-hidden row. They only appear on
-            untagged channels (the attached slice above is empty then), so they get the full width and
-            can't fight the fit measurer. Extras past the row clip like any overflow. */}
-        {shownSuggestions.map((s) => (
-          <SuggestedChip
-            key={s.tag.id}
-            suggestion={s}
-            onAccept={() => onAcceptSuggestion?.(s.tag.id)}
-            onDismiss={() => onDismissSuggestion?.(s.tag.id)}
-          />
-        ))}
-      </div>
+          <div ref={rowRef} className="flex items-center gap-1 min-w-0 flex-1 overflow-hidden">
+            {attached.slice(0, visible).map((tg) => (
+              <TagChip
+                key={tg.id}
+                tag={tg}
+                onClick={onChipClick ? () => onChipClick(tg.id, tg.name) : undefined}
+                title={
+                  onChipClick ? t("channels.row.filterFeedByTag", { name: tg.name }) : undefined
+                }
+              />
+            ))}
+            {hidden > 0 && (
+              <button
+                ref={overflowPop.refs.setReference}
+                type="button"
+                className={`${pillClass} hover:text-fg transition`}
+                {...overflowPop.getReferenceProps()}
+              >
+                +{hidden}
+              </button>
+            )}
+          </div>
+        </>
+      )}
 
       <button
         ref={editPop.refs.setReference}

frontend/src/components/Channels.tsx

@@ -205,14 +205,15 @@ export default function Channels() {
   const dismissSuggestion = (cid: string, tagId: number) =>
     setDismissed((prev) => new Set(prev).add(sKey(cid, tagId)));
   const acceptSuggestion = (cid: string, tagId: number) => {
-    // Optimistically drop it from the suggestions cache so the ghost chip vanishes at once; toggleTag
-    // attaches the real tag (its onSuccess re-invalidates suggestions + the channel detail).
+    // Optimistically drop the WHOLE channel from the suggestions cache: attaching any tag makes it
+    // "tagged", which the server excludes from suggestions entirely — so its other ghost chips would
+    // vanish on the next refetch anyway. Removing them now keeps the ghost lane and the attached lane
+    // mutually exclusive (no transient of both showing). toggleTag attaches the real tag; its onSuccess
+    // re-invalidates suggestions + the channel detail.
     qc.setQueryData<TagSuggestions>(qk.tagSuggestions(), (old) => {
       if (!old?.[cid]) return old;
-      const rest = old[cid].filter((s) => s.tag_id !== tagId);
       const next = { ...old };
-      if (rest.length) next[cid] = rest;
-      else delete next[cid];
+      delete next[cid];
       return next;
     });
     toggleTag(cid, tagId, false);