D6 reference snapshots

D6 is disabled by default. Set D6_ENABLED=true on the showcase-harness Railway service to enable. The other env vars below (D6_MODE, LGP_BASE_URL, etc.) only matter once D6_ENABLED is true. Without the flag the driver short-circuits with an aggregate green "D6 disabled" signal on every tick and emits no per-feature rows.

Per-feature ParitySnapshot JSON files captured against the LangGraph-Python (LGP) showcase — the reference implementation the D6 probe compares every other showcase against.

What lives here

One JSON file per D5FeatureType:

fixtures/d6-reference/
  agentic-chat.json
  tool-rendering.json
  shared-state-read.json
  shared-state-write.json
  hitl-approve-deny.json
  hitl-text-input.json
  gen-ui-headless.json
  gen-ui-custom.json
  mcp-apps.json
  subagents.json

Each file conforms to the ParitySnapshot schema in src/probes/helpers/parity-compare.ts:

domElements — flat list of relevant chat-content DOM elements (sorted by testId, tag, classes).
toolCalls — ordered list of tool-call names emitted on the SSE stream (concatenated across turns).
streamProfile — { ttft_ms, p50_chunk_ms, total_chunks } aggregated across the conversation's turns.
contractShape — field path → JS-type string for the union of every SSE payload observed.

The files are NOT shipped in git in this commit — the .gitkeep reserves the directory and the helper writes snapshots at runtime when the LGP showcase is online.

When to refresh

Weekly cron — the showcase-harness scheduler runs the capture job once a week to pick up upstream LGP runtime/agent drift.
Manual trigger — operators can re-capture on demand:
- after an LGP showcase redeploy (especially LGP runtime / agent changes),
- after a D5 fixture update (fixtures/d5/*.json) — fixtures drive what the model says, which changes tool calls and contract shape,
- after a parity-tolerances change in parity-compare.ts — re-baseline so previous captures' timing aren't unfairly compared against new bounds,
- after an ag-ui protocol bump that changes wire-level event names.

If you're unsure whether the snapshots are stale, run the D6 probe — captured-vs-reference drift on the timing axes is a clean signal that the reference is older than the deployment.

How to invoke

The everyday operator path is the CLI script — it wires all deps (Playwright launcher, SSE interceptor, conversation runner, DOM serializer, file writer) for you:

# From showcase/harness/:
LGP_BASE_URL=https://langgraph-python.up.railway.app \
  npx tsx scripts/d6-capture-references.ts

The script (showcase/harness/scripts/d6-capture-references.ts) accepts:

--integration <slug> — default langgraph-python.
--base-url <url> — else falls back to the LGP_BASE_URL env.
--feature <type> — optional, target a single featureType.

It exits 0 when every result is captured or skipped, and 1 when any result is failed. Production wiring (driver + scheduler) is integrated with B13.

For programmatic / test callers, the helper lives at src/probes/helpers/reference-capture.ts and exposes two entry points:

import {
  captureReferenceForFeature,
  captureAllReferences,
  serializeRelevantDom,
  defaultWriteSnapshot,
} from "../../src/probes/helpers/reference-capture.js";
import { attachSseInterceptor } from "../../src/probes/helpers/sse-interceptor.js";
import { runConversation } from "../../src/probes/helpers/conversation-runner.js";

// Production callers compose their own `launchBrowser` (real Playwright) and
// pass the helper's defaults for the remaining slots. Tests inject scripted
// fakes for ALL deps — there is no "default" launcher exported from the
// helper module today; the CLI script above contains the canonical wiring.
const results = await captureAllReferences(
  {
    baseUrl: "https://langgraph-python.up.railway.app",
    integrationSlug: "langgraph-python",
    outputDir: path.resolve(__dirname, "../../fixtures/d6-reference"),
  },
  {
    launchBrowser: yourLauncher,
    attachSseInterceptor,
    runConversation,
    serializeDom: serializeRelevantDom,
    writeSnapshot: defaultWriteSnapshot,
  },
);

yourLauncher is a placeholder — production callers compose a real Playwright launcher. See scripts/d6-capture-references.ts for the canonical wiring (browser launch, page setup, teardown).

What to verify after capture

Every featureType in D5_REGISTRY produced a file (no failed results in the return array).
streamProfile.total_chunks > 0 on every captured snapshot — a zero-chunk profile means the SSE interceptor missed the stream and the snapshot is unusable.
toolCalls matches the D5 fixture's expected sequence — if not, either the fixture or the capture is wrong; check fixtures/d5/<feature>.json first.
Open the JSON file diff — keys should be sorted, domElements sorted by (testId, tag, classes), toolCalls in arrival order. Diff-stable output is non-negotiable: a noisy diff on re-capture means either non-determinism in the LGP run or a regression in the helper's normalization.

Failure modes

The helper is fail-closed: any failure (browser launch, navigation, conversation failure_turn, DOM serialization, write) returns { status: "failed", reason } WITHOUT writing a partial file. An absent reference is correctly handled by the D6 driver (skips the comparison with a "no reference" note); a corrupt one would silently invalidate the parity verdict for that featureType.

If the capture run reports failed for a featureType, do NOT delete the older snapshot in place — leave it until a successful run replaces it atomically.