Human Interaction Chaos

Streaming UIs degrade in two directions. The server side breaks when chunks stall, truncate, or corrupt; the human side breaks when users act mid-generation: cancelling a response, smashing the retry button, backgrounding the tab, editing the prompt while chunks are still arriving, or navigating away. The userInteraction namespace covers the human side.

Triggers are scenario events, not rules. They fire on a fixed millisecond schedule measured from chaos start, never consult the PRNG, and carry no matchers, probabilities, or counting options. The same config always produces the same interaction sequence.

Surface

await injectChaos(page, {
  seed: 42,
  userInteraction: {
    cancelStreamAfterMs: 4000,
    retryStorm: { count: 5, intervalMs: 200 },
    tabHidden: { afterMs: 1000, durationMs: 3000 },
    blurWindow: { afterMs: 2000, durationMs: 500 },
    promptEditDuringResponse: { afterMs: 1500, simulateTypingMs: 800 },
    navigateAway: { afterMs: 6000, target: '/' },
  },
});

All fields are optional. Every trigger emits ui:* events tagged with user:* phases, so timeline reporting renders human actions inline with transport chaos.

Triggers

cancelStreamAfterMs

Cancels every in-flight streaming connection at the scheduled time:

• fetch streams abort. The engine threads its own AbortController into every request (merged with any signal the app already passed), so the consumer observes a real AbortError on reader.read(), exactly as if the user hit stop.
• SSE sources close and dispatch a synthetic error event so onerror handlers engage.
• WebSockets close; the app observes a normal close event.

Connections opened after the trigger fires are unaffected. One ui:user-cancel event is emitted per cancelled connection with detail.url, detail.targetTransport, and detail.connectionId when the connection carried one; when nothing is in flight, a single applied: false event with reason: 'no-active-streams' records the miss.

Fixture-driven stream replay in block-upstream mode never touches the network, so it is not cancellable through this trigger.

retryStorm

Rapid-fire synthetic clicks against a selector, simulating a user hammering retry while a request fails or a stream stalls. Defaults to [data-chaos-retry]; the element is re-queried before every click so re-rendered buttons stay reachable. One ui:retry-storm event per click; one selector-not-found diagnostic per storm when nothing matches.

retryStorm: { count: 5, intervalMs: 200, afterMs: 1000, selector: '#retry' }

tabHidden

Simulates backgrounding the tab: document.visibilityState reports 'hidden', document.hidden reports true, and a synthetic visibilitychange event fires at both edges. The tab is never actually backgrounded, so the run stays deterministic and headless-safe. The override restores itself after durationMs and on engine stop.

blurWindow

Dispatches synthetic blur then focus events on the window, durationMs apart. Focus-state properties are not overridden; apps that listen for the events see them, apps that poll document.hasFocus() do not.

promptEditDuringResponse

Focuses the prompt input (default [data-chaos-prompt]) and types text (default ' (edited)') character by character, spreading keystrokes evenly across simulateTypingMs. Each character updates .value and dispatches a bubbling input event.

navigateAway

Calls location.assign(target) after afterMs. The navigation tears down the page context, so assert on the destination page or on beforeunload side effects; the ui:navigate event is emitted immediately before the navigation so log sinks attached earlier in the run still capture it.

Composing with streaming chaos

Triggers compose with every transport rule and the ai shorthand. The classic incident reproductions are one-liners:

// User gives up before the first chunk arrives.
await injectChaos(page, {
  ai: { firstChunkDelayMs: 3000 },
  userInteraction: { cancelStreamAfterMs: 1500 },
});

// Retry-loop incident: slow first chunk plus a retry storm.
await injectChaos(page, {
  ai: { firstChunkDelayMs: 2500 },
  userInteraction: { retryStorm: { count: 3, intervalMs: 300, afterMs: 500 } },
});

The ai-mobile-interrupt preset packages the mobile flavor: the tab reports hidden for 3 seconds while the stream drops mid-generation. See presets.

Presets and profiles

Presets and profiles may carry userInteraction. Merging is per trigger: when several sources set the same trigger, the later source wins that trigger (user config beats presets; profile overrides beat everything). Rule arrays append; triggers replace.

Environment notes

• Selector- and document-based triggers need a DOM. Non-DOM contexts (service workers) skip them with a console warning; cancelStreamAfterMs still works wherever fetch is patched.
• All pending trigger timers clear on stop(), and the visibility override restores itself, so nothing leaks across tests.