From 02bba578d9dc5391ff3ad208199668dd29f296de Mon Sep 17 00:00:00 2001
From: brsbl <57682038+brsbl@users.noreply.github.com>
Date: Thu, 27 Aug 2026 06:02:25 +0000
Subject: [PATCH] Resolve archived thread names in sidebar mentions

---
 .../src/components/sidebar/ThreadRow.test.tsx |  40 ++++++
 .../components/thread/ThreadTitleMentions.tsx | 131 ++++++++++++++----
 2 files changed, 142 insertions(+), 29 deletions(-)

diff --git a/apps/app/src/components/sidebar/ThreadRow.test.tsx b/apps/app/src/components/sidebar/ThreadRow.test.tsx
index 396f56ed4e..29d5c4636c 100644
--- a/apps/app/src/components/sidebar/ThreadRow.test.tsx
+++ b/apps/app/src/components/sidebar/ThreadRow.test.tsx
@@ -6,6 +6,7 @@ import {
   fireEvent,
   render,
   screen,
+  waitFor,
 } from "@testing-library/react";
 import { MemoryRouter } from "react-router-dom";
 import type { ReactNode } from "react";
@@ -45,6 +46,7 @@ import {
 import { splitLayoutAtom } from "@/lib/split-layout/atoms";
 import { SPLIT_LAYOUT_STORAGE_KEY } from "@/lib/split-layout/persistence";
 import { NO_COLLAPSED_CHILD_ACTIVITY } from "@bb/client-core";
+import { sdk } from "@/lib/sdk";
 
 vi.mock("@/components/thread/ThreadActionsMenu", () => ({
   ThreadActionsContextMenu: ({ children }: { children: ReactNode }) => (
@@ -653,6 +655,44 @@ describe("ThreadRow", () => {
     expect(screen.getByTitle(resolvedTitle)).not.toBeNull();
   });
 
+  it("resolves a serialized thread title mention outside the sidebar cache", async () => {
+    const resolveMentions = vi
+      .spyOn(sdk.threads, "resolveMentions")
+      .mockResolvedValue([
+        {
+          threadId: "thr_dcwivn5n8w",
+          projectId: "proj_mentioned",
+          label: "Mention target",
+        },
+      ]);
+
+    render(
+      <ThreadTitleMentionResourcesProvider
+        sectionNamesById={new Map()}
+        projectNamesById={new Map()}
+        threadById={new Map()}
+      >
+        <ThreadRowTestHarness
+          thread={createThread({
+            title: "Continue from @thread:thr_dcwivn5n8w",
+            titleFallback: "Continue from @thread:thr_dcwivn5n8w",
+          })}
+        />
+      </ThreadTitleMentionResourcesProvider>,
+    );
+
+    expect(screen.queryByText("thr_dcwivn5n8w")).toBeNull();
+    expect(
+      screen.getByRole("link", { name: "Open Continue from Thread" }),
+    ).not.toBeNull();
+    await waitFor(() => expect(resolveMentions).toHaveBeenCalledTimes(1));
+    expect(screen.getByText("Mention target")).not.toBeNull();
+    expect(screen.queryByText("thr_dcwivn5n8w")).toBeNull();
+    expect(
+      screen.getByRole("link", { name: "Open Continue from Mention target" }),
+    ).not.toBeNull();
+  });
+
   it("marks a child from another project with the project name", () => {
     const { container } = render(
       <ThreadTitleMentionResourcesProvider
diff --git a/apps/app/src/components/thread/ThreadTitleMentions.tsx b/apps/app/src/components/thread/ThreadTitleMentions.tsx
index 9911764ccb..6931ed58ce 100644
--- a/apps/app/src/components/thread/ThreadTitleMentions.tsx
+++ b/apps/app/src/components/thread/ThreadTitleMentions.tsx
@@ -486,20 +486,30 @@ function threadMentionResource(
   };
 }
 
+const UNRESOLVED_THREAD_MENTION_LABEL = "Thread";
+
+function unresolvedThreadMentionResource(
+  threadId: string,
+): PromptMentionResource {
+  return {
+    kind: "thread",
+    threadId,
+    label: UNRESOLVED_THREAD_MENTION_LABEL,
+  };
+}
+
 function resolveTitleMentionResource(
   token: string,
   resources: ThreadTitleMentionResources,
-): PromptMentionResource {
+): PromptMentionResource | null {
   const serializedValue = token.slice(1);
   if (serializedValue.startsWith("thread:")) {
     const threadId = serializedValue.slice("thread:".length);
-    return (
-      threadMentionResource(threadId, resources) ?? {
-        kind: "thread",
-        threadId,
-        label: threadId,
-      }
-    );
+    const resource = threadMentionResource(threadId, resources);
+    if (resource !== null || isRawThreadId(threadId)) {
+      return resource;
+    }
+    return { kind: "thread", threadId, label: threadId };
   }
 
   if (serializedValue.startsWith("project:")) {
@@ -533,12 +543,17 @@ function resolveTitleMentionResource(
 }
 
 interface ThreadTitleTextSegment {
-  rawThreadId: string | null;
+  unresolvedThreadId: string | null;
   resource: PromptMentionResource | null;
   serializedText: string | null;
   text: string;
 }
 
+function serializedThreadMentionId(token: string): string | null {
+  const prefix = "@thread:";
+  return token.startsWith(prefix) ? token.slice(prefix.length) : null;
+}
+
 function threadTitleTextSegments(
   title: string,
   resources: ThreadTitleMentionResources,
@@ -567,21 +582,28 @@ function threadTitleTextSegments(
     }
     if (match.index > cursor) {
       segments.push({
-        rawThreadId: null,
+        unresolvedThreadId: null,
         resource: null,
         serializedText: null,
         text: title.slice(cursor, match.index),
       });
     }
+    const serializedThreadId =
+      rawThreadId === null ? serializedThreadMentionId(token) : null;
     const resource =
       rawThreadId === null
         ? resolveTitleMentionResource(token, resources)
         : threadMentionResource(rawThreadId, resources);
+    const unresolvedThreadId =
+      resource === null ? (rawThreadId ?? serializedThreadId) : null;
     segments.push({
-      rawThreadId: resource === null ? rawThreadId : null,
+      unresolvedThreadId,
       resource,
-      serializedText: resource === null ? null : token,
-      text: resource?.label ?? token,
+      serializedText:
+        resource === null && unresolvedThreadId === null ? null : token,
+      text:
+        resource?.label ??
+        (serializedThreadId === null ? token : UNRESOLVED_THREAD_MENTION_LABEL),
     });
     cursor = matchEnd;
   }
@@ -589,7 +611,7 @@ function threadTitleTextSegments(
   if (segments.length === 0) {
     return [
       {
-        rawThreadId: null,
+        unresolvedThreadId: null,
         resource: null,
         serializedText: null,
         text: title,
@@ -598,7 +620,7 @@ function threadTitleTextSegments(
   }
   if (cursor < title.length) {
     segments.push({
-      rawThreadId: null,
+      unresolvedThreadId: null,
       resource: null,
       serializedText: null,
       text: title.slice(cursor),
@@ -620,10 +642,32 @@ export function resolveThreadTitleDisplayText(
 /** Resolves serialized mentions in a thread title to one plain display label. */
 export function useThreadTitleDisplayText(title: string): string {
   const resources = useContext(ThreadTitleMentionResourcesContext);
-  return useMemo(
-    () => resolveThreadTitleDisplayText(title, resources),
+  const segments = useMemo(
+    () => threadTitleTextSegments(title, resources),
     [resources, title],
   );
+  const unresolvedThreadIds = useMemo(() => {
+    const threadIds = new Set<string>();
+    for (const segment of segments) {
+      if (segment.unresolvedThreadId !== null) {
+        threadIds.add(segment.unresolvedThreadId);
+      }
+    }
+    return [...threadIds];
+  }, [segments]);
+  const resolvedThreadsById = useRawThreadMentionResources(unresolvedThreadIds);
+  return useMemo(
+    () =>
+      segments
+        .map((segment) =>
+          segment.unresolvedThreadId === null
+            ? segment.text
+            : (resolvedThreadsById.get(segment.unresolvedThreadId)?.label ??
+              segment.text),
+        )
+        .join(""),
+    [resolvedThreadsById, segments],
+  );
 }
 
 /**
@@ -711,17 +755,26 @@ export function useRawThreadMentionResources(
   const resources = useContext(ThreadTitleMentionResourcesContext);
   const queryClient = useContext(QueryClientContext);
   const batch = useContext(RawThreadMentionBatchContext);
+  const resolver = useContext(RawThreadMentionResolverContext);
+  const resolutionContext =
+    batch === EMPTY_RAW_THREAD_MENTION_BATCH ? resolver : batch;
   useEffect(() => {
+    let registeredCount = 0;
     for (const threadId of threadIds) {
       const sidebarResource = threadMentionResource(threadId, resources);
       const cachedThread = queryClient?.getQueryData<ThreadResponse>(
         threadQueryKey(threadId),
       );
-      if (sidebarResource === null && cachedThread === undefined) {
-        batch.register(threadId);
+      if (
+        sidebarResource === null &&
+        cachedThread === undefined &&
+        registeredCount < THREAD_MENTION_RESOLVE_MAX_IDS
+      ) {
+        resolutionContext.register(threadId);
+        registeredCount += 1;
       }
     }
-  }, [batch, queryClient, resources, threadIds]);
+  }, [queryClient, resolutionContext, resources, threadIds]);
 
   return useMemo(() => {
     const resourceById = new Map<string, PromptMentionResource>();
@@ -743,25 +796,43 @@ export function useRawThreadMentionResources(
         });
         continue;
       }
-      const batchResource = batch.resourceById.get(threadId);
+      const batchResource = resolutionContext.resourceById.get(threadId);
       if (batchResource !== undefined) {
         resourceById.set(threadId, batchResource);
       }
     }
     return resourceById;
-  }, [batch.resourceById, queryClient, resources, threadIds]);
+  }, [queryClient, resolutionContext.resourceById, resources, threadIds]);
+}
+
+interface ResolvingThreadTitleMentionProps {
+  renderFallbackPill: boolean;
+  serializedText: string;
+  threadId: string;
 }
 
-function RawThreadTitleMention({ threadId }: { threadId: string }) {
+function ResolvingThreadTitleMention({
+  renderFallbackPill,
+  serializedText,
+  threadId,
+}: ResolvingThreadTitleMentionProps) {
   const resource = useRawThreadMentionResource(threadId);
   if (resource === null) {
-    return threadId;
+    return renderFallbackPill ? (
+      <PromptMentionPill
+        interactive={false}
+        resource={unresolvedThreadMentionResource(threadId)}
+        serializedText={serializedText}
+      />
+    ) : (
+      threadId
+    );
   }
   return (
     <PromptMentionPill
       interactive={false}
       resource={resource}
-      serializedText={threadId}
+      serializedText={serializedText}
     />
   );
 }
@@ -769,10 +840,12 @@ function RawThreadTitleMention({ threadId }: { threadId: string }) {
 function ThreadTitleMentionsContent({ title }: { title: string }) {
   const resources = useContext(ThreadTitleMentionResourcesContext);
   return threadTitleTextSegments(title, resources).map((segment, index) =>
-    segment.rawThreadId !== null ? (
-      <RawThreadTitleMention
-        key={`${index}:${segment.rawThreadId}`}
-        threadId={segment.rawThreadId}
+    segment.unresolvedThreadId !== null && segment.serializedText !== null ? (
+      <ResolvingThreadTitleMention
+        key={`${index}:${segment.unresolvedThreadId}`}
+        renderFallbackPill={segment.serializedText.startsWith("@thread:")}
+        serializedText={segment.serializedText}
+        threadId={segment.unresolvedThreadId}
       />
     ) : segment.resource === null || segment.serializedText === null ? (
       segment.text