deer-flow/backend/docs/REPLAY_E2E.md

Record/Replay E2E — front-back contract verification

Deterministic, key-free end-to-end checks that a backend change can't silently break the frontend (and vice-versa). Two complementary layers, fed by a single recording.

Why

The mock-based frontend e2e hand-writes the backend's JSON/SSE, so a backend schema or SSE change passes green ("fake green"). These layers replay a recorded real run against the real backend (and, for Layer 2, the real frontend), so contract drift turns the build red instead.

The two layers

• Layer 1 — backend golden (tests/test_replay_golden.py): replays a fixture through the real FastAPI gateway with ReplayChatModel and asserts the streamed SSE event sequence equals a committed golden. Fast, no browser. Guards protocol shape.
• Layer 2 — full-stack render (frontend/tests/e2e-real-backend/): real Next.js + real gateway (replay model) + Chromium; asserts the replayed auto-title and a follow-up suggestion render in the browser. Guards semantic render. (Complementary to Layer 1 — neither subsumes the other.)

Layer 2 also hosts cross-stack contract scenarios — the dangerous class where a backend change silently breaks a frontend assumption and both sides' unit tests stay green. See below.

Cross-stack scenario: multi-run render order (multi-run-order.spec.ts)

Regression guard for issue #3352 (after context compression, refreshing a thread rendered history out of order). Root cause was a front-back desync: backend RunManager.list_by_thread returns runs newest-first (PR #2932), while the frontend (core/threads/hooks.ts) iterated runs and prepended each loaded page — inverting chronological order once the checkpoint no longer held the older messages. The backend ordering test was green throughout, and the frontend regression unit test hardcodes "backend returns newest-first" in a mock, so only a real frontend against a real backend catches the desync.

This scenario does not record a conversation. It uses a test-only seeder (tests/seed_runs_router.py, mounted on the replay gateway only when DEERFLOW_ENABLE_TEST_SEED=1) to stand up a thread with ≥2 runs and per-run message events — and deliberately no checkpoint, which is the #3352 precondition: it forces the frontend's per-run reload path to be the sole source of truth so the ordering bug becomes observable. The seeder writes through the gateway's own run/event stores using the request's auth context, so the real list_by_thread → /runs/{id}/messages → prepend path runs live. Reverting the #3354 frontend fix turns this spec red.

How replay works

tests/replay_provider.py::ReplayChatModel returns recorded assistant turns keyed by a normalized hash of the model input (strips <system-reminder>, dates, UUIDs, tmp paths). A miss raises loudly rather than passing silently. The system prompt is made environment-independent by pinning skills + extensions empty and disabling memory/summarization (tests/_replay_fixture.py::build_config_yaml), so a fixture replays the same across machines, days, and CI. Replaying needs no API key.

Record a new scenario (needs a real key — dev machine only)

Recording drives the real frontend so captured inputs match exactly what the browser sends; fixtures contain no API key.

# 1. drive the real frontend against a real-model gateway, capturing model calls
OPENAI_API_KEY=... OPENAI_API_BASE=<openai-compatible-endpoint>/v1 \
  DEERFLOW_RECORD_OUT=/tmp/rec/turns.jsonl RECORD_MODEL=<model> \
  bash -c 'cd frontend && pnpm exec playwright test -c playwright.record.config.ts'

# 2. stitch the capture into a fixture
cd backend && uv run python scripts/build_fixture_from_jsonl.py \
  --jsonl /tmp/rec/turns.jsonl --meta /tmp/rec/turns.jsonl.meta.json \
  --out tests/fixtures/replay/<scenario>.<mode>.json --model <model>

# 3. regenerate the committed golden
DEERFLOW_WRITE_GOLDEN=1 PYTHONPATH=. uv run pytest tests/test_replay_golden.py

Run (no key)

cd backend  && PYTHONPATH=. uv run pytest tests/test_replay_golden.py          # Layer 1
cd frontend && pnpm exec playwright test -c playwright.real-backend.config.ts  # Layer 2

CI

.github/workflows/replay-e2e.yml runs both layers on changes to either side of the contract (frontend/**, backend/app/gateway/**, backend/packages/harness/**, fixtures). DOM assertions are the gate; the rendered screenshot + Playwright HTML report are uploaded as a CI artifact.

Known limitations

• Visual regression baselines are OS-specific, so they are a local dev gate only (gitignored); CI uploads the render as an artifact for human review instead of hard-asserting a cross-OS baseline.
• Fixtures are coupled to the recording-time prompt; if new environment-dependent content enters the system prompt, extend the normalization in replay_provider.py (or pin it in build_config_yaml).
• Re-record a scenario if the agent graph changes how many model calls it makes — the replay raises loudly on a hash miss pointing at the divergence.