Build Recoverable navigation session

Model the lifecycle before the UI

Turn the navigation session blueprint into an explicit aggregate boundary owned by the application.

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Implement every command and event pair

Make intent, actor authority, allowed source state, committed state, and emitted fact reviewable together.

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Persist restart-safe records

Separate business identity, provider evidence, command receipts, immutable facts, audit, and downstream delivery.

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Make concurrency and replay deterministic

Apply optimistic expected versions and aggregate-scoped idempotency before executing effects.

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Control effects and unknown outcomes

Commit outbox intent atomically, execute effects outside the transaction, and reconcile ambiguous results.

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Run all hostile fixture scenarios

Exercise the success path plus replay, concurrency, state, and response-loss failures without an account.

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Trace the Weekend Trip Planner capstone

Follow the maintained source through domain rules, adapter seam, repository transaction, HTTP boundary, UI evidence, and restart test.

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Qualify the real integration boundary

Replace only reviewed adapter seams and collect independent production evidence without weakening application invariants.

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Application-owned reliability scaffolds

The aggregate and SQL examples implement host truth; the fixture clients call the credential-free Journey Lab. Replace only the separately reviewed provider adapter seam.

type State = "draft" | "preview" | "navigating" | "rerouting" | "arrived" | "ended";
type CommandName = "calculate_route" | "start_guidance" | "request_reroute" | "accept_reroute" | "confirm_arrival" | "end_session";

type Command = {
  name: CommandName;
  aggregateId: string;
  expectedVersion: number;
  idempotencyKey: string;
};

const transitions = {
  "calculate_route": { from: ["draft", "preview"], to: "preview", event: "route.calculated" },
  "start_guidance": { from: ["preview"], to: "navigating", event: "navigation.started" },
  "request_reroute": { from: ["navigating", "rerouting"], to: "rerouting", event: "reroute.requested" },
  "accept_reroute": { from: ["rerouting"], to: "navigating", event: "route.updated" },
  "confirm_arrival": { from: ["navigating"], to: "arrived", event: "navigation.arrived" },
  "end_session": { from: ["preview", "navigating", "rerouting", "arrived"], to: "ended", event: "navigation.ended" },
} as const;

export function decide(current: { state: State | null; version: number }, command: Command) {
  const rule = transitions[command.name];
  if (command.expectedVersion !== current.version) throw new Error("version_conflict");
  if (!rule.from.includes(current.state as never)) throw new Error("invalid_transition");
  return {
    state: rule.to as State,
    version: current.version + 1,
    event: rule.event,
    idempotencyKey: command.idempotencyKey,
  };
}

// Persist the result, immutable event, audit row, and outbox intent atomically.
// Store the first result by idempotencyKey before executing another effect.

Exit with reviewable evidence

Trace every external claim to an indexed source