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

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

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}`,
+  )
+})