perf(app): use cursor session history loading (#17329)

2 files changed, 56 insertions, 8 deletions

diff --git a/packages/app/src/context/global-sync/session-prefetch.test.ts b/packages/app/src/context/global-sync/session-prefetch.test.ts
index f039b02ca..1ce833469 100644
--- a/packages/app/src/context/global-sync/session-prefetch.test.ts
+++ b/packages/app/src/context/global-sync/session-prefetch.test.ts
@@ -5,6 +5,7 @@ import {
   getSessionPrefetch,
   runSessionPrefetch,
   setSessionPrefetch,
+  shouldSkipSessionPrefetch,
 } from "./session-prefetch"
 
 describe("session prefetch", () => {
@@ -16,11 +17,12 @@ describe("session prefetch", () => {
       directory: "/tmp/a",
       sessionID: "ses_1",
       limit: 200,
+      cursor: "abc",
       complete: false,
       at: 123,
     })
 
-    expect(getSessionPrefetch("/tmp/a", "ses_1")).toEqual({ limit: 200, complete: false, at: 123 })
+    expect(getSessionPrefetch("/tmp/a", "ses_1")).toEqual({ limit: 200, cursor: "abc", complete: false, at: 123 })
     expect(getSessionPrefetch("/tmp/b", "ses_1")).toBeUndefined()
 
     clearSessionPrefetch("/tmp/a", ["ses_1"])
@@ -38,26 +40,57 @@ describe("session prefetch", () => {
         sessionID: "ses_2",
         task: async () => {
           calls += 1
-          return { limit: 100, complete: true, at: 456 }
+          return { limit: 100, cursor: "next", complete: true, at: 456 }
         },
       })
 
     const [a, b] = await Promise.all([run(), run()])
 
     expect(calls).toBe(1)
-    expect(a).toEqual({ limit: 100, complete: true, at: 456 })
-    expect(b).toEqual({ limit: 100, complete: true, at: 456 })
+    expect(a).toEqual({ limit: 100, cursor: "next", complete: true, at: 456 })
+    expect(b).toEqual({ limit: 100, cursor: "next", complete: true, at: 456 })
   })
 
   test("clears a whole directory", () => {
-    setSessionPrefetch({ directory: "/tmp/d", sessionID: "ses_1", limit: 10, complete: true, at: 1 })
-    setSessionPrefetch({ directory: "/tmp/d", sessionID: "ses_2", limit: 20, complete: false, at: 2 })
-    setSessionPrefetch({ directory: "/tmp/e", sessionID: "ses_1", limit: 30, complete: true, at: 3 })
+    setSessionPrefetch({ directory: "/tmp/d", sessionID: "ses_1", limit: 10, cursor: "a", complete: true, at: 1 })
+    setSessionPrefetch({ directory: "/tmp/d", sessionID: "ses_2", limit: 20, cursor: "b", complete: false, at: 2 })
+    setSessionPrefetch({ directory: "/tmp/e", sessionID: "ses_1", limit: 30, cursor: "c", complete: true, at: 3 })
 
     clearSessionPrefetchDirectory("/tmp/d")
 
     expect(getSessionPrefetch("/tmp/d", "ses_1")).toBeUndefined()
     expect(getSessionPrefetch("/tmp/d", "ses_2")).toBeUndefined()
-    expect(getSessionPrefetch("/tmp/e", "ses_1")).toEqual({ limit: 30, complete: true, at: 3 })
+    expect(getSessionPrefetch("/tmp/e", "ses_1")).toEqual({ limit: 30, cursor: "c", complete: true, at: 3 })
+  })
+
+  test("refreshes stale first-page prefetched history", () => {
+    expect(
+      shouldSkipSessionPrefetch({
+        message: true,
+        info: { limit: 200, cursor: "x", complete: false, at: 1 },
+        chunk: 200,
+        now: 1 + 15_001,
+      }),
+    ).toBe(false)
+  })
+
+  test("keeps deeper or complete history cached", () => {
+    expect(
+      shouldSkipSessionPrefetch({
+        message: true,
+        info: { limit: 400, cursor: "x", complete: false, at: 1 },
+        chunk: 200,
+        now: 1 + 15_001,
+      }),
+    ).toBe(true)
+
+    expect(
+      shouldSkipSessionPrefetch({
+        message: true,
+        info: { limit: 120, complete: true, at: 1 },
+        chunk: 200,
+        now: 1 + 15_001,
+      }),
+    ).toBe(true)
   })
 })
diff --git a/packages/app/src/context/global-sync/session-prefetch.ts b/packages/app/src/context/global-sync/session-prefetch.ts
index 10877b063..608561f85 100644
--- a/packages/app/src/context/global-sync/session-prefetch.ts
+++ b/packages/app/src/context/global-sync/session-prefetch.ts
@@ -4,10 +4,23 @@ export const SESSION_PREFETCH_TTL = 15_000
 
 type Meta = {
   limit: number
+  cursor?: string
   complete: boolean
   at: number
 }
 
+export function shouldSkipSessionPrefetch(input: { message: boolean; info?: Meta; chunk: number; now?: number }) {
+  if (input.message) {
+    if (!input.info) return true
+    if (input.info.complete) return true
+    if (input.info.limit > input.chunk) return true
+  } else {
+    if (!input.info) return false
+  }
+
+  return (input.now ?? Date.now()) - input.info.at < SESSION_PREFETCH_TTL
+}
+
 const cache = new Map<string, Meta>()
 const inflight = new Map<string, Promise<Meta | undefined>>()
 const rev = new Map<string, number>()
@@ -53,11 +66,13 @@ export function setSessionPrefetch(input: {
   directory: string
   sessionID: string
   limit: number
+  cursor?: string
   complete: boolean
   at?: number
 }) {
   cache.set(key(input.directory, input.sessionID), {
     limit: input.limit,
+    cursor: input.cursor,
     complete: input.complete,
     at: input.at ?? Date.now(),
   })