fix(app): make session navigation stable and fast (#33569)

Co-authored-by: Brendan Allan <git@brendonovich.dev>

packages/app/src/utils/session-placement.test.ts

@@ -0,0 +1,38 @@
+import { describe, expect, test } from "bun:test"
+import { ServerConnection } from "@/context/server"
+import { createSessionPlacementStore } from "./session-placement"
+
+describe("session placement", () => {
+  const local = ServerConnection.Key.make("http://localhost:4096")
+  const remote = ServerConnection.Key.make("https://example.com")
+
+  test("aliases a leaf and root without crossing servers", () => {
+    const store = createSessionPlacementStore()
+    store.set({ server: local, leafID: "child", rootID: "root", directory: "/repo" })
+    store.set({ server: remote, leafID: "child", rootID: "other", directory: "/remote" })
+
+    expect(store.get(local, "child")).toEqual({ rootID: "root", directory: "/repo" })
+    expect(store.get(local, "root")).toEqual({ rootID: "root", directory: "/repo" })
+    expect(store.get(remote, "child")).toEqual({ rootID: "other", directory: "/remote" })
+  })
+
+  test("inherits known placement for in-app child navigation", () => {
+    const store = createSessionPlacementStore()
+    store.set({ server: local, leafID: "parent", rootID: "root", directory: "/repo" })
+
+    expect(store.inherit(local, "parent", "child")).toEqual({ rootID: "root", directory: "/repo" })
+    expect(store.get(local, "child")).toEqual({ rootID: "root", directory: "/repo" })
+    expect(store.inherit(local, "missing", "unknown")).toBeUndefined()
+  })
+
+  test("bounds retained placement aliases", () => {
+    const store = createSessionPlacementStore()
+    for (let index = 0; index < 300; index++) {
+      store.set({ server: local, leafID: `leaf-${index}`, rootID: `root-${index}`, directory: `/repo/${index}` })
+    }
+
+    expect(store.size()).toBeLessThanOrEqual(256)
+    expect(store.get(local, "leaf-0")).toBeUndefined()
+    expect(store.get(local, "leaf-299")).toEqual({ rootID: "root-299", directory: "/repo/299" })
+  })
+})

packages/app/src/utils/session-placement.ts

@@ -0,0 +1,41 @@
+import { ServerConnection } from "@/context/server"
+
+export type SessionPlacement = {
+  rootID: string
+  directory: string
+}
+
+export function createSessionPlacementStore() {
+  const placements = new Map<string, SessionPlacement>()
+  const limit = 256
+  const key = (server: ServerConnection.Key, sessionID: string) => `${server}\0${sessionID}`
+  const write = (id: string, placement: SessionPlacement) => {
+    placements.delete(id)
+    placements.set(id, placement)
+    while (placements.size > limit) placements.delete(placements.keys().next().value!)
+  }
+
+  return {
+    get(server: ServerConnection.Key, sessionID: string) {
+      const id = key(server, sessionID)
+      const placement = placements.get(id)
+      if (placement) write(id, placement)
+      return placement
+    },
+    set(input: SessionPlacement & { server: ServerConnection.Key; leafID: string }) {
+      const placement = { rootID: input.rootID, directory: input.directory }
+      write(key(input.server, input.leafID), placement)
+      write(key(input.server, input.rootID), placement)
+      return placement
+    },
+    inherit(server: ServerConnection.Key, sourceID: string, leafID: string) {
+      const placement = placements.get(key(server, sourceID))
+      if (!placement) return
+      write(key(server, leafID), placement)
+      return placement
+    },
+    size() {
+      return placements.size
+    },
+  }
+}