perf(client): reuse unchanged pr links while streaming

apps/web/src/state/pullRequests.ts

@@ -502,13 +502,28 @@ function savedPullRequestKey(
     : `${environmentId}:${threadPullRequestKeyOf({ ...reference, host: reference.host })}`;
 }
 
+// Any thread's streaming tick rebuilds the map below from every linked pull request. Links keep
+// their identity until they change, so each link's URL is parsed once, not once per tick.
+const savedLinkSummaries = new WeakMap<
+  ThreadPullRequestLink,
+  { readonly projectId: ProjectId; readonly summary: PullRequestSummary | null }
+>();
+
+function savedLinkSummary(link: ThreadPullRequestLink, projectId: ProjectId) {
+  const cached = savedLinkSummaries.get(link);
+  if (cached?.projectId === projectId) return cached.summary;
+  const summary = threadPullRequestLinkToSummary(link, projectId);
+  savedLinkSummaries.set(link, { projectId, summary });
+  return summary;
+}
+
 const savedPullRequestSummariesAtom = Atom.make((get) => {
   const summaries = new Map<string, PullRequestSummary>();
   for (const thread of get(environmentThreadShells.threadShellsAtom)) {
     for (const link of visibleThreadPullRequests(thread.pullRequests)) {
-      const summary = threadPullRequestLinkToSummary(link, thread.projectId);
+      const summary = savedLinkSummary(link, thread.projectId);
       if (summary === null) continue;
-      const key = savedPullRequestKey(thread.environmentId, link);
+      const key = `${thread.environmentId}:${threadPullRequestKeyOf(link)}`;
       summaries.set(key, newestPullRequestSummary(summaries.get(key) ?? null, summary) ?? summary);
     }
   }

packages/client-runtime/src/state/shellReducer.test.ts

@@ -420,6 +420,34 @@ describe("applyShellStreamEvents", () => {
     expect(applyShellStreamEvents(seed, [])).toBe(seed);
   });
 
+  it("keeps an unchanged links array when a streaming row changes", () => {
+    const link: ThreadPullRequestLink = {
+      host: "github.com",
+      repository: "pingdotgg/t3code",
+      number: 3,
+      url: "https://github.com/pingdotgg/t3code/pull/3",
+      source: "agent",
+      linkedAt: "2026-06-20T00:00:00.000Z",
+      snapshot: null,
+      stack: null,
+    };
+    const linked = { ...a, pullRequests: [link] };
+    const seed = { ...v2ShellSnapshot, threads: [linked, b], snapshotSequence: 4 };
+    const tick = { ...linked, itemCount: 9, pullRequests: [{ ...link }] };
+    const relinked = { ...linked, pullRequests: [{ ...link, number: 4 }] };
+
+    expect(applyShellStreamEvent(seed, update(5, tick)).threads[0]?.pullRequests).toBe(
+      linked.pullRequests,
+    );
+    const batched = applyShellStreamEvents(seed, [update(5, tick), update(6, { ...b })]);
+    expect(batched.threads.find((thread) => thread.id === a.id)?.pullRequests).toBe(
+      linked.pullRequests,
+    );
+    expect(applyShellStreamEvent(seed, update(5, relinked)).threads[0]?.pullRequests).toBe(
+      relinked.pullRequests,
+    );
+  });
+
   it("does not advance the cursor for an unknown future event", () => {
     const events = [
       { kind: "future.event", sequence: 99 } as never,

packages/client-runtime/src/state/shellReducer.ts

@@ -22,6 +22,19 @@ export function sameThreadPullRequests(
   return left === right || sameLinks(left, right);
 }
 
+// A streaming thread resends its whole shell on each tick. Keeping the prior links array when it
+// has not changed lets later comparisons stop at identity and keeps per-link caches warm.
+function retainUnchangedLinks(
+  previous: OrchestrationV2ThreadShell | undefined,
+  next: OrchestrationV2ThreadShell,
+): OrchestrationV2ThreadShell {
+  if (previous?.pullRequests === undefined || next.pullRequests === undefined) return next;
+  if (previous.pullRequests === next.pullRequests) return next;
+  return sameLinks(previous.pullRequests, next.pullRequests)
+    ? { ...next, pullRequests: previous.pullRequests }
+    : next;
+}
+
 /**
  * Links are compared apart from the rest of the row because a deferred snapshot arrives without
  * them; such a row keeps its links until they fill in.
@@ -39,7 +52,7 @@ export function reuseUnchangedThreadShells(
     const candidate =
       thread.pullRequests === undefined && prior.pullRequests !== undefined
         ? { ...thread, pullRequests: prior.pullRequests }
-        : thread;
+        : retainUnchangedLinks(prior, thread);
     const retained = sameThreadShell(prior, candidate) ? prior : candidate;
     if (retained !== thread) changed = true;
     return retained;
@@ -160,7 +173,8 @@ export function applyShellStreamEvent(
         event.location === "active"
           ? snapshot.threads.find((thread) => thread.id === event.thread.id)
           : undefined;
-      if (existing !== undefined && sameThreadShell(existing, event.thread)) {
+      const thread = retainUnchangedLinks(existing, event.thread);
+      if (existing !== undefined && sameThreadShell(existing, thread)) {
         return { ...snapshot, snapshotSequence: event.sequence };
       }
       const withoutThread = (threads: OrchestrationV2ShellSnapshot["threads"]) =>
@@ -169,7 +183,7 @@ export function applyShellStreamEvent(
         ...snapshot,
         threads:
           event.location === "active"
-            ? upsertById(snapshot.threads, event.thread)
+            ? upsertById(snapshot.threads, thread)
             : withoutThread(snapshot.threads),
         // The archive has its own bounded query/subscription. Older servers may
         // still send archive-located deltas here; remove them from the normal
@@ -243,8 +257,9 @@ export function applyShellStreamEvents(
         const id = event.thread.id;
         if (event.location === "active") {
           const previous = threads.get(id);
-          if (previous !== undefined && sameThreadShell(previous, event.thread)) break;
-          threads.set(event.thread);
+          const thread = retainUnchangedLinks(previous, event.thread);
+          if (previous !== undefined && sameThreadShell(previous, thread)) break;
+          threads.set(thread);
         } else {
           threads.remove(id);
         }

packages/source-control-core/src/shared/threadPullRequests.ts

@@ -142,8 +142,25 @@ export function makeThreadPullRequests(
     return `${normalized.host}/${normalized.repository}#${normalized.number}`;
   }
 
+  // Shells keep their links array while a run streams, and several components read the
+  // current pull request on each shell change, so resolve each array's chains once.
+  const currentByLinks = new WeakMap<
+    ReadonlyArray<ThreadPullRequestLink>,
+    ThreadCurrentPullRequest | null
+  >();
+
   function resolveThreadCurrentPullRequest(
     links: ReadonlyArray<ThreadPullRequestLink>,
+  ): ThreadCurrentPullRequest | null {
+    const cached = currentByLinks.get(links);
+    if (cached !== undefined) return cached;
+    const current = resolveUncachedThreadCurrentPullRequest(links);
+    currentByLinks.set(links, current);
+    return current;
+  }
+
+  function resolveUncachedThreadCurrentPullRequest(
+    links: ReadonlyArray<ThreadPullRequestLink>,
   ): ThreadCurrentPullRequest | null {
     const visible = visibleThreadPullRequests(links);
     if (visible.length === 0) return null;