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

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

packages/app/e2e/performance/README.md

@@ -18,6 +18,8 @@ bun run test:bench
 The suite contains:
 
 - cold and hot session-tab timing
+- home-session click timing split between content and titlebar-tab paint
+- single-session tab close timing through stable home restoration
 - cached session repaint and mutation tracing
 - streaming timeline throughput, RAF-gap, long-task, geometry, and remount diagnostics
 

packages/app/e2e/performance/timeline/first-navigation-benchmark.spec.ts

@@ -0,0 +1,87 @@
+import { expectSessionTitle } from "../../utils/waits"
+import { benchmark, expect } from "../benchmark"
+import { measureFirstNavigation } from "./first-navigation-probe"
+import { fixture } from "./session-timeline-stress.fixture"
+import {
+  installStressSessionTabs,
+  installTimelineSettings,
+  mockStressTimeline,
+  stressDraftHref,
+  stressSessionHref,
+} from "./timeline-test-helpers"
+import { waitForStableTimeline } from "./session-tab-switch-probe"
+
+const contentSelector = '[data-message-id], [data-component="prompt-input"]'
+const draftID = "draft_first_navigation"
+
+benchmark.describe("performance: first navigation paint", () => {
+  benchmark("opens an unvisited session tab without a blank frame", async ({ page, report }) => {
+    await setup(page)
+    const href = stressSessionHref(fixture.targetID)
+    const result = await measureFirstNavigation(page, {
+      href,
+      destinationPath: href,
+      sourceSelector: messageSelector(fixture.expected.sourceMessageIDs.at(-1)!),
+      destinationSelector: messageSelector(fixture.expected.targetMessageIDs.at(-1)!),
+      contentSelector,
+      navigate: async () => {
+        await page.locator(`[data-slot="titlebar-tabs"] a[href="${href}"]`).first().click()
+        await expectSessionTitle(page, fixture.expected.targetTitle)
+      },
+    })
+    report(result)
+    expect(result.summary.blankSamples).toBe(0)
+    expect(result.summary.unknownSamples).toBe(0)
+  })
+
+  benchmark("opens the new session page before its lazy module is used", async ({ page, report }) => {
+    await setup(page, draftID)
+    const href = stressDraftHref(draftID)
+    const result = await measureFirstNavigation(page, {
+      href,
+      destinationPath: href,
+      sourceSelector: messageSelector(fixture.expected.sourceMessageIDs.at(-1)!),
+      destinationSelector: '[data-component="prompt-input"]',
+      contentSelector,
+      navigate: async () => {
+        await page.locator(`[data-slot="titlebar-tabs"] a[href="${href}"]`).first().click()
+        await expect(page.locator('[data-component="prompt-input"]')).toBeVisible()
+      },
+    })
+    report(result)
+    expect(result.summary.blankSamples).toBe(0)
+    expect(result.summary.unknownSamples).toBe(0)
+  })
+
+  benchmark("opens a child session without a blank frame", async ({ page, report }) => {
+    await setup(page)
+    const href = stressSessionHref(fixture.childID)
+    const result = await measureFirstNavigation(page, {
+      href,
+      destinationPath: href,
+      sourceSelector: messageSelector(fixture.expected.sourceMessageIDs.at(-1)!),
+      destinationSelector: messageSelector(fixture.expected.childMessageIDs.at(-1)!),
+      contentSelector,
+      navigate: async () => {
+        await page.locator(`a[href="${href}"]`, { has: page.locator('[data-component="task-tool-card"]') }).click()
+        await expectSessionTitle(page, fixture.expected.childTitle)
+      },
+    })
+    report(result)
+    expect(result.summary.blankSamples).toBe(0)
+    expect(result.summary.unknownSamples).toBe(0)
+  })
+})
+
+async function setup(page: Parameters<typeof mockStressTimeline>[0], draft?: string) {
+  await mockStressTimeline(page)
+  await installTimelineSettings(page)
+  await installStressSessionTabs(page, draft ? { draftID: draft } : undefined)
+  await page.goto(stressSessionHref(fixture.sourceID))
+  await expectSessionTitle(page, fixture.expected.sourceTitle)
+  await waitForStableTimeline(page, fixture.expected.sourceMessageIDs.at(-1)!)
+}
+
+function messageSelector(id: string) {
+  return `[data-message-id="${id}"]`
+}

packages/app/e2e/performance/timeline/first-navigation-metrics.ts

@@ -0,0 +1,34 @@
+export type FirstNavigationSample = {
+  observedAtMs: number
+  source: boolean
+  destination: boolean
+  content: boolean
+  pathname?: string
+  center?: string
+}
+
+function category(sample: FirstNavigationSample) {
+  if (sample.destination && !sample.source) return "destination"
+  if (sample.source && !sample.destination) return "source"
+  if (!sample.content) return "blank"
+  return "unknown"
+}
+
+export function summarizeFirstNavigation(samples: FirstNavigationSample[]) {
+  const categories = samples.map(category)
+  const stable = categories.findIndex(
+    (value, index) =>
+      value === "destination" &&
+      categories[index + 1] === "destination" &&
+      categories[index + 2] === "destination",
+  )
+  return {
+    samples: samples.length,
+    firstDestinationObservedMs: samples[categories.indexOf("destination")]?.observedAtMs ?? null,
+    stableDestinationObservedMs: stable === -1 ? null : samples[stable + 2]!.observedAtMs,
+    sourceSamples: categories.filter((value) => value === "source").length,
+    blankSamples: categories.filter((value) => value === "blank").length,
+    unknownSamples: categories.filter((value) => value === "unknown").length,
+    destinationSamples: categories.filter((value) => value === "destination").length,
+  }
+}

packages/app/e2e/performance/timeline/first-navigation-probe.ts

@@ -0,0 +1,85 @@
+import type { Page } from "@playwright/test"
+import { summarizeFirstNavigation, type FirstNavigationSample } from "./first-navigation-metrics"
+
+type FirstNavigationProbe = {
+  samples: FirstNavigationSample[]
+  stop: () => void
+}
+
+export async function measureFirstNavigation(
+  page: Page,
+  input: {
+    href: string
+    destinationPath: string
+    sourceSelector: string
+    destinationSelector: string
+    contentSelector: string
+    navigate: () => Promise<void>
+  },
+) {
+  await page.evaluate(
+    ({ href, destinationPath, sourceSelector, destinationSelector, contentSelector }) => {
+      const samples: FirstNavigationSample[] = []
+      let started: number | undefined
+      let running = true
+      const visible = (selector: string) =>
+        [...document.querySelectorAll<HTMLElement>(selector)].some((element) => {
+          const rect = element.getBoundingClientRect()
+          const style = getComputedStyle(element)
+          return rect.width > 0 && rect.height > 0 && style.visibility !== "hidden" && style.display !== "none"
+        })
+      const sample = () => {
+        if (!running || started === undefined) return
+        requestAnimationFrame(() => {
+          setTimeout(() => {
+            if (!running || started === undefined) return
+            samples.push({
+              observedAtMs: performance.now() - started,
+              source: visible(sourceSelector),
+              destination: `${location.pathname}${location.search}` === destinationPath && visible(destinationSelector),
+              content: visible(contentSelector),
+              pathname: `${location.pathname}${location.search}`,
+              center: document.elementFromPoint(innerWidth / 2, innerHeight / 2)?.textContent?.slice(0, 80),
+            })
+            sample()
+          }, 0)
+        })
+      }
+      document.addEventListener(
+        "click",
+        (event) => {
+          const link = event.target instanceof Element ? event.target.closest("a") : undefined
+          if (link?.getAttribute("href") !== href) return
+          started = performance.now()
+          sample()
+        },
+        { capture: true, once: true },
+      )
+      ;(window as Window & { __firstNavigationProbe?: FirstNavigationProbe }).__firstNavigationProbe = {
+        samples,
+        stop: () => {
+          running = false
+        },
+      }
+    },
+    {
+      href: input.href,
+      destinationPath: input.destinationPath,
+      sourceSelector: input.sourceSelector,
+      destinationSelector: input.destinationSelector,
+      contentSelector: input.contentSelector,
+    },
+  )
+  await input.navigate()
+  await page.waitForFunction(() => {
+    const samples = (window as Window & { __firstNavigationProbe?: FirstNavigationProbe }).__firstNavigationProbe?.samples
+    if (!samples) return false
+    return samples.length >= 3 && samples.slice(-3).every((sample) => sample.destination && !sample.source)
+  })
+  const samples = await page.evaluate(() => {
+    const probe = (window as Window & { __firstNavigationProbe?: FirstNavigationProbe }).__firstNavigationProbe!
+    probe.stop()
+    return probe.samples
+  })
+  return { summary: summarizeFirstNavigation(samples), samples }
+}

packages/app/e2e/performance/timeline/home-tab-navigation-benchmark.spec.ts

@@ -0,0 +1,114 @@
+import { benchmark, expect } from "../benchmark"
+import { expectSessionTitle } from "../../utils/waits"
+import { measureNavigationMilestones } from "./navigation-milestones"
+import { fixture } from "./session-timeline-stress.fixture"
+import {
+  installStressSessionTabs,
+  installTimelineSettings,
+  mockStressTimeline,
+  stressSessionHref,
+} from "./timeline-test-helpers"
+import { waitForStableTimeline } from "./session-tab-switch-probe"
+
+const homeRow = '[data-component="home-session-row"]'
+const homeShell = '[data-component="home-session-search"]'
+
+benchmark.describe("performance: home and tab navigation", () => {
+  benchmark("opens a home session and paints its titlebar tab", async ({ page, report }) => {
+    await setup(page, [])
+    await page.goto("/")
+    const row = page.locator(homeRow).filter({ hasText: fixture.expected.targetTitle }).first()
+    await expect(row).toBeVisible()
+    const href = stressSessionHref(fixture.targetID)
+    const result = await measureNavigationMilestones(page, {
+      triggerSelector: homeRow,
+      milestones: {
+        content: { selector: messageSelector(fixture.expected.targetMessageIDs.at(-1)!) },
+        tab: { selector: `[data-slot="titlebar-tabs"] a[href="${href}"]` },
+      },
+      navigate: async () => {
+        await row.click()
+        await expectSessionTitle(page, fixture.expected.targetTitle)
+      },
+    })
+    report(result)
+    await expect(page.locator(`[data-slot="titlebar-tabs"] a[href="${href}"]`)).toContainText(
+      fixture.expected.targetTitle,
+    )
+  })
+
+  benchmark("stages the review body after cold session content", async ({ page, report }) => {
+    await setup(page, [])
+    await page.goto("/")
+    const row = page.locator(homeRow).filter({ hasText: fixture.expected.targetTitle }).first()
+    await expect(row).toBeVisible()
+    const result = await page.evaluate(
+      ({ rowSelector, title, contentSelector }) =>
+        new Promise<{ contentBeforeReview: boolean; samples: number }>((resolve) => {
+          let samples = 0
+          const sample = () => {
+            samples++
+            const content = !!document.querySelector(contentSelector)
+            const review = !!document.querySelector('[data-component="session-review"]')
+            if (content && !review) {
+              resolve({ contentBeforeReview: true, samples })
+              return
+            }
+            if (content && review) {
+              resolve({ contentBeforeReview: false, samples })
+              return
+            }
+            requestAnimationFrame(sample)
+          }
+          const target = [...document.querySelectorAll<HTMLElement>(rowSelector)].find((item) =>
+            item.textContent?.includes(title),
+          )
+          if (!target) throw new Error(`Home session row not found: ${title}`)
+          target.click()
+          requestAnimationFrame(sample)
+        }),
+      {
+        rowSelector: homeRow,
+        title: fixture.expected.targetTitle,
+        contentSelector: messageSelector(fixture.expected.targetMessageIDs.at(-1)!),
+      },
+    )
+    report(result)
+    expect(result.contentBeforeReview).toBe(true)
+    await expect(page.locator('[data-component="session-review"]')).toBeVisible()
+  })
+
+  benchmark("closes the only session tab and paints home", async ({ page, report }) => {
+    await setup(page, [fixture.sourceID])
+    const href = stressSessionHref(fixture.sourceID)
+    await page.goto(href)
+    await expectSessionTitle(page, fixture.expected.sourceTitle)
+    await waitForStableTimeline(page, fixture.expected.sourceMessageIDs.at(-1)!)
+    const tab = page.locator(`[data-slot="titlebar-tabs"] a[href="${href}"]`).first()
+    const close = tab.locator("..").locator('[data-component="icon-button-v2"]')
+    await expect(close).toBeVisible()
+    const result = await measureNavigationMilestones(page, {
+      triggerSelector: '[data-slot="titlebar-tabs"] [data-component="icon-button-v2"]',
+      milestones: {
+        home: { selector: homeShell },
+        row: { selector: homeRow },
+        tabRemoved: { selector: `[data-slot="titlebar-tabs"] a[href="${href}"]`, visible: false },
+      },
+      navigate: async () => {
+        await close.click()
+        await expect(page).toHaveURL("/")
+      },
+    })
+    report(result)
+  })
+})
+
+async function setup(page: Parameters<typeof mockStressTimeline>[0], sessionIDs: string[]) {
+  await mockStressTimeline(page)
+  await installTimelineSettings(page)
+  await installStressSessionTabs(page, { sessionIDs })
+}
+
+function messageSelector(id: string) {
+  return `[data-message-id="${id}"]`
+}

packages/app/e2e/performance/timeline/navigation-milestones.ts

@@ -0,0 +1,123 @@
+import type { Page } from "@playwright/test"
+
+export type NavigationMilestoneSample = {
+  observedAtMs: number
+  milestones: Record<string, boolean>
+}
+
+export function summarizeNavigationMilestones(samples: NavigationMilestoneSample[]) {
+  const names = Object.keys(samples[0]?.milestones ?? {})
+  const summarize = (matches: (sample: NavigationMilestoneSample) => boolean) => {
+    const first = samples.find(matches)
+    const stable = samples.findIndex(
+      (sample, index) =>
+        index + 2 < samples.length && matches(sample) && matches(samples[index + 1]!) && matches(samples[index + 2]!),
+    )
+    return {
+      firstObservedMs: first?.observedAtMs ?? null,
+      stableObservedMs: stable === -1 ? null : samples[stable + 2]!.observedAtMs,
+    }
+  }
+  return {
+    samples: samples.length,
+    milestones: Object.fromEntries(names.map((name) => [name, summarize((sample) => sample.milestones[name] === true)])),
+    all: summarize((sample) => names.every((name) => sample.milestones[name] === true)),
+  }
+}
+
+type NavigationMilestoneProbe = {
+  samples: NavigationMilestoneSample[]
+  stop: () => void
+}
+
+export async function measureNavigationMilestones(
+  page: Page,
+  input: {
+    triggerSelector: string
+    milestones: Record<string, { selector: string; visible?: boolean }>
+    navigate: () => Promise<void>
+  },
+) {
+  await page.evaluate(({ triggerSelector, milestones }) => {
+    const samples: NavigationMilestoneSample[] = []
+    const streaks = new Map<string, number>()
+    const marked = new Set<string>()
+    let started: number | undefined
+    let running = true
+    const visible = (selector: string) =>
+      [...document.querySelectorAll<HTMLElement>(selector)].some((element) => {
+        const rect = element.getBoundingClientRect()
+        const style = getComputedStyle(element)
+        return rect.width > 0 && rect.height > 0 && style.visibility !== "hidden" && style.display !== "none"
+      })
+    const sample = () => {
+      if (!running || started === undefined) return
+      requestAnimationFrame(() => {
+        setTimeout(() => {
+          if (!running || started === undefined) return
+          const current = Object.fromEntries(
+            Object.entries(milestones).map(([name, milestone]) => [
+              name,
+              milestone.visible === false ? !document.querySelector(milestone.selector) : visible(milestone.selector),
+            ]),
+          )
+          samples.push({
+            observedAtMs: performance.now() - started,
+            milestones: current,
+          })
+          Object.entries(current).forEach(([name, value]) => {
+            if (!value) {
+              streaks.set(name, 0)
+              return
+            }
+            if (!marked.has(`${name}.first`)) {
+              performance.mark(`opencode.navigation.${name}.first`)
+              marked.add(`${name}.first`)
+            }
+            const streak = (streaks.get(name) ?? 0) + 1
+            streaks.set(name, streak)
+            if (streak === 3) performance.mark(`opencode.navigation.${name}.stable`)
+          })
+          const all = Object.values(current).every(Boolean)
+          const allStreak = all ? (streaks.get("all") ?? 0) + 1 : 0
+          streaks.set("all", allStreak)
+          if (all && !marked.has("all.first")) {
+            performance.mark("opencode.navigation.all.first")
+            marked.add("all.first")
+          }
+          if (allStreak === 3) performance.mark("opencode.navigation.all.stable")
+          sample()
+        }, 0)
+      })
+    }
+    document.addEventListener(
+      "click",
+      (event) => {
+        if (!(event.target instanceof Element) || !event.target.closest(triggerSelector)) return
+        started = performance.now()
+        performance.mark("opencode.navigation.click")
+        sample()
+      },
+      { capture: true, once: true },
+    )
+    ;(window as Window & { __navigationMilestones?: NavigationMilestoneProbe }).__navigationMilestones = {
+      samples,
+      stop: () => {
+        running = false
+      },
+    }
+  }, { triggerSelector: input.triggerSelector, milestones: input.milestones })
+  await input.navigate()
+  await page.waitForFunction(() => {
+    const samples = (window as Window & { __navigationMilestones?: NavigationMilestoneProbe }).__navigationMilestones
+      ?.samples
+    if (!samples || samples.length < 3) return false
+    return samples.slice(-3).every((sample) => Object.values(sample.milestones).every(Boolean))
+  })
+  const samples = await page.evaluate(() => {
+    const probe = (window as Window & { __navigationMilestones?: NavigationMilestoneProbe }).__navigationMilestones!
+    probe.stop()
+    return probe.samples
+  })
+  return { summary: summarizeNavigationMilestones(samples), samples }
+}

packages/app/e2e/performance/timeline/session-tab-flash.spec.ts

@@ -47,3 +47,21 @@ benchmark("samples cached session repaint after the click", async ({ page, repor
   report(compressCachedRepaintTrace(result))
   expect(result.samples.length).toBeGreaterThan(0)
 })
+
+benchmark("prefetches every open session tab", async ({ page, report }) => {
+  const prefetched = new Set<string>()
+  await mockStressTimeline(page, {
+    onMessages: (input) => {
+      if (!input.before && input.phase === "start") prefetched.add(input.sessionID)
+    },
+  })
+  await installStressSessionTabs(page, {
+    sessionIDs: [fixture.sourceID, fixture.targetID, fixture.childID],
+  })
+  await installTimelineSettings(page)
+  await page.goto(stressSessionHref(fixture.sourceID))
+  await expectSessionTitle(page, fixture.expected.sourceTitle)
+
+  await expect.poll(() => prefetched.has(fixture.childID)).toBe(true)
+  report({ prefetched: [...prefetched] })
+})

packages/app/e2e/performance/timeline/session-timeline-stress.fixture.ts

@@ -23,6 +23,7 @@ const words = [
 
 const sourceID = "ses_smoke_source"
 const targetID = "ses_smoke_target"
+const childID = "ses_smoke_child"
 const directory = "C:/OpenCode/SmokeProject"
 const projectID = "proj_smoke_timeline"
 const model = { providerID: "opencode", modelID: "claude-opus-4-6", variant: "max" }
@@ -126,9 +127,11 @@ function toolPart(
   tool: string,
   input: Record<string, unknown>,
   outputLength = 160,
+  metadataOverride?: Record<string, unknown>,
 ): MessagePart {
   const metadata =
-    tool === "apply_patch"
+    metadataOverride ??
+    (tool === "apply_patch"
       ? { files: [patchFile(index, "update"), patchFile(index + 1, index % 2 === 0 ? "add" : "delete")] }
       : tool === "edit" || tool === "write"
         ? {
@@ -138,7 +141,7 @@ function toolPart(
           }
         : tool === "question"
           ? { answers: [["Proceed"], ["Keep sample output"]] }
-          : {}
+          : {})
   return {
     id: id(`prt_tool_${tool}_${partIndex}`, index),
     type: "tool",
@@ -244,7 +247,25 @@ function turn(index: number): Message[] {
 const targetMessages = Array.from({ length: 72 }, (_, index) => turn(index)).flat()
 const sourceMessages = Array.from({ length: 12 }, (_, index) => [
   userMessage(sourceID, index + 1000, 120),
-  assistantMessage(sourceID, index + 1000, id("msg_user", index + 1000), [textPart(index + 1000, 0, 240)]),
+  assistantMessage(sourceID, index + 1000, id("msg_user", index + 1000), [
+    textPart(index + 1000, 0, 240),
+    ...(index === 11
+      ? [
+          toolPart(
+            index + 1000,
+            1,
+            "task",
+            { description: "Inspect child navigation", subagent_type: "explore" },
+            160,
+            { sessionId: childID },
+          ),
+        ]
+      : []),
+  ]),
+]).flat()
+const childMessages = Array.from({ length: 4 }, (_, index) => [
+  userMessage(childID, index + 2000, 120),
+  assistantMessage(childID, index + 2000, id("msg_user", index + 2000), [textPart(index + 2000, 0, 240)]),
 ]).flat()
 
 function renderable(part: MessagePart) {
@@ -298,19 +319,34 @@ export const fixture = {
       version: "dev",
       time: { created: 1700000001000, updated: 1700000001000 },
     },
+    {
+      id: childID,
+      parentID: sourceID,
+      slug: "child",
+      projectID,
+      directory,
+      title: "Inspect child navigation",
+      version: "dev",
+      time: { created: 1700000002000, updated: 1700000002000 },
+    },
   ],
   sourceID,
   targetID,
-  messages: { [sourceID]: sourceMessages, [targetID]: targetMessages },
+  childID,
+  messages: { [sourceID]: sourceMessages, [targetID]: targetMessages, [childID]: childMessages },
   expected: {
     sourceTitle: "Uncommitted changes inquiry",
     targetTitle: "Example Game: sample jump movement & sample physics analysis",
+    childTitle: "Inspect child navigation",
     sourceMessageIDs: sourceMessages
       .filter((message) => message.info.role === "user")
       .map((message) => message.info.id),
     targetMessageIDs: targetMessages
       .filter((message) => message.info.role === "user")
       .map((message) => message.info.id),
+    childMessageIDs: childMessages
+      .filter((message) => message.info.role === "user")
+      .map((message) => message.info.id),
     targetPartIDs: targetMessages.flatMap((message) =>
       orderedParts(message)
         .filter(renderable)

packages/app/e2e/performance/timeline/timeline-test-helpers.ts

@@ -1,7 +1,7 @@
 import type { Page } from "@playwright/test"
 import { base64Encode } from "@opencode-ai/core/util/encode"
 import { mockOpenCodeServer } from "../../utils/mock-server"
-import { fixture } from "./session-timeline-stress.fixture"
+import { fixture, pageMessages } from "./session-timeline-stress.fixture"
 
 export async function installTimelineSettings(page: Page) {
   await page.addInitScript(() => {
@@ -9,6 +9,7 @@ export async function installTimelineSettings(page: Page) {
       "settings.v3",
       JSON.stringify({
         general: {
+          newLayoutDesigns: true,
           editToolPartsExpanded: true,
           shellToolPartsExpanded: true,
           showReasoningSummaries: true,
@@ -19,20 +20,24 @@ export async function installTimelineSettings(page: Page) {
   })
 }
 
-export function mockStressTimeline(page: Page) {
+export function mockStressTimeline(
+  page: Page,
+  input?: { onMessages?: (input: { sessionID: string; before?: string; phase: "start" | "end" }) => void },
+) {
   return mockOpenCodeServer(page, {
     sessions: fixture.sessions,
     provider: fixture.provider,
     directory: fixture.directory,
     project: fixture.project,
-    pageMessages: (sessionID) => ({ items: fixture.messages[sessionID as keyof typeof fixture.messages] ?? [] }),
+    pageMessages,
+    onMessages: input?.onMessages,
   })
 }
 
-export async function installStressSessionTabs(page: Page) {
-  const server = `http://${process.env.PLAYWRIGHT_SERVER_HOST ?? "127.0.0.1"}:${process.env.PLAYWRIGHT_SERVER_PORT ?? "4096"}`
+export async function installStressSessionTabs(page: Page, input?: { draftID?: string; sessionIDs?: string[] }) {
+  const server = stressServer()
   await page.addInitScript(
-    ({ directory, sourceID, targetID, dirBase64, server }) => {
+    ({ directory, sessionIDs, dirBase64, server, draftID }) => {
       localStorage.setItem(
         "opencode.global.dat:server",
         JSON.stringify({
@@ -43,25 +48,36 @@ export async function installStressSessionTabs(page: Page) {
       localStorage.setItem(
         "opencode.global.dat:tabs",
         JSON.stringify(
-          [sourceID, targetID].map((sessionId) => ({
-            type: "session",
-            server,
-            dirBase64,
-            sessionId,
-          })),
+          [
+            ...sessionIDs.map((sessionId) => ({
+              type: "session",
+              server,
+              dirBase64,
+              sessionId,
+            })),
+            ...(draftID ? [{ type: "draft", draftID, server, directory }] : []),
+          ],
         ),
       )
     },
     {
       directory: fixture.directory,
-      sourceID: fixture.sourceID,
-      targetID: fixture.targetID,
+      sessionIDs: input?.sessionIDs ?? [fixture.sourceID, fixture.targetID],
       dirBase64: base64Encode(fixture.directory),
       server,
+      draftID: input?.draftID,
     },
   )
 }
 
 export function stressSessionHref(sessionID: string) {
-  return `/${base64Encode(fixture.directory)}/session/${sessionID}`
+  return `/server/${base64Encode(stressServer())}/session/${sessionID}`
+}
+
+export function stressDraftHref(draftID: string) {
+  return `/new-session?draftId=${encodeURIComponent(draftID)}`
+}
+
+function stressServer() {
+  return `http://${process.env.PLAYWRIGHT_SERVER_HOST ?? "127.0.0.1"}:${process.env.PLAYWRIGHT_SERVER_PORT ?? "4096"}`
 }

packages/app/e2e/performance/unit/first-navigation-metrics.test.ts

@@ -0,0 +1,32 @@
+import { expect, test } from "bun:test"
+import { summarizeFirstNavigation } from "../timeline/first-navigation-metrics"
+
+test("reports blank frames before first destination and stable paint", () => {
+  expect(
+    summarizeFirstNavigation([
+      { observedAtMs: 16, source: true, destination: false, content: true },
+      { observedAtMs: 32, source: false, destination: false, content: false },
+      { observedAtMs: 48, source: false, destination: true, content: true },
+      { observedAtMs: 64, source: false, destination: true, content: true },
+      { observedAtMs: 80, source: false, destination: true, content: true },
+    ]),
+  ).toEqual({
+    samples: 5,
+    firstDestinationObservedMs: 48,
+    stableDestinationObservedMs: 80,
+    sourceSamples: 1,
+    blankSamples: 1,
+    unknownSamples: 0,
+    destinationSamples: 3,
+  })
+})
+
+test("does not report stability for interrupted destination frames", () => {
+  expect(
+    summarizeFirstNavigation([
+      { observedAtMs: 16, source: false, destination: true, content: true },
+      { observedAtMs: 32, source: false, destination: false, content: true },
+      { observedAtMs: 48, source: false, destination: true, content: true },
+    ]).stableDestinationObservedMs,
+  ).toBeNull()
+})

packages/app/e2e/performance/unit/navigation-milestones.test.ts

@@ -0,0 +1,34 @@
+import { expect, test } from "bun:test"
+import { summarizeNavigationMilestones } from "../timeline/navigation-milestones"
+
+test("reports first and stable paint for each navigation milestone", () => {
+  expect(
+    summarizeNavigationMilestones([
+      { observedAtMs: 16, milestones: { content: false, tab: false } },
+      { observedAtMs: 32, milestones: { content: true, tab: false } },
+      { observedAtMs: 48, milestones: { content: true, tab: true } },
+      { observedAtMs: 64, milestones: { content: true, tab: true } },
+      { observedAtMs: 80, milestones: { content: true, tab: true } },
+    ]),
+  ).toEqual({
+    samples: 5,
+    milestones: {
+      content: { firstObservedMs: 32, stableObservedMs: 64 },
+      tab: { firstObservedMs: 48, stableObservedMs: 80 },
+    },
+    all: { firstObservedMs: 48, stableObservedMs: 80 },
+  })
+})
+
+test("reports missing stability when a milestone appears in the final samples", () => {
+  expect(
+    summarizeNavigationMilestones([
+      { observedAtMs: 16, milestones: { content: false } },
+      { observedAtMs: 32, milestones: { content: true } },
+    ]),
+  ).toEqual({
+    samples: 2,
+    milestones: { content: { firstObservedMs: 32, stableObservedMs: null } },
+    all: { firstObservedMs: 32, stableObservedMs: null },
+  })
+})

packages/app/e2e/performance/unit/timeline-test-helpers.test.ts

@@ -0,0 +1,10 @@
+import { expect, test } from "bun:test"
+import { base64Encode } from "@opencode-ai/core/util/encode"
+import { fixture } from "../timeline/session-timeline-stress.fixture"
+import { stressSessionHref } from "../timeline/timeline-test-helpers"
+
+test("builds stress session links for the benchmark server", () => {
+  expect(stressSessionHref(fixture.sourceID)).toBe(
+    `/server/${base64Encode("http://127.0.0.1:4096")}/session/${fixture.sourceID}`,
+  )
+})