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packages/foundation/flow/workflow/src/compensation/saga/saga.md

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+# saga
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+
+## Purpose
+
+`Saga` is the dedicated, opinionated orchestrator for the textbook saga
+pattern: sequential business steps where every successful step registers
+its inverse so that a later failure can roll back every side effect in
+strict reverse order. Compared to `WorkflowEngine`, `Saga` is intentionally
+narrower — it has no `onError: "continue"` mode, no transition hooks, and
+no lifecycle hook registry. Callers reach for it when they want the smaller
+surface area and the explicit per-step semantics.
+
+The class owns its own `Compensator` and resets it at the start of every
+`execute` call, so a single `Saga` instance can be run repeatedly without
+leaking state across runs.
+
+## Features
+
+- `addStep(step)` fluent registration.
+- Sequential execution with first-failure short-circuit.
+- Automatic reverse-order compensation via the internal `Compensator`.
+- `continueCompensationOnError` (default `true`) — forwards to the
+  compensator.
+- Skipped steps recorded but not compensated.
+- Injectable `Clock` propagates to the compensator too.
+
+## Usage: Basic Example
+
+```ts
+import { createSaga, createStep } from "@suaveplan/workflow";
+
+const saga = createSaga<{ orderId: string }>({
+	id: "booking",
+	name: "Booking saga",
+});
+
+saga
+	.addStep(
+		createStep({
+			id: "reserve",
+			name: "Reserve seats",
+			execute: (ctx) => reserveSeats(ctx),
+			compensate: (ctx) => releaseSeats(ctx),
+		}),
+	)
+	.addStep(
+		createStep({
+			id: "charge",
+			name: "Charge payment",
+			execute: (ctx) => chargeCard(ctx),
+			compensate: (ctx) => refundCard(ctx),
+		}),
+	);
+
+const result = await saga.execute({ orderId: "ord-1" });
+```
+
+## Usage: Advanced Example
+
+```ts
+import { createSaga, createStep } from "@suaveplan/workflow";
+
+const fakeClock = () => 1_000;
+const saga = createSaga<{ id: string }>({
+	id: "two-phase",
+	name: "Two-phase commit",
+	continueCompensationOnError: false,
+	clock: fakeClock,
+});
+
+saga.addStep(
+	createStep({
+		id: "lock",
+		name: "Lock resource",
+		execute: (ctx) => acquireLock(ctx.id),
+		compensate: (ctx) => releaseLock(ctx.id),
+	}),
+);
+saga.addStep(
+	createStep({
+		id: "commit",
+		name: "Commit",
+		execute: () => {
+			throw new Error("conflict");
+		},
+	}),
+);
+
+const result = await saga.execute({ id: "row-7" });
+expect(result.status).toBe("failed");
+expect(result.compensationRecords.length).toBe(1);
+```
+
+## API Reference
+
+- `SagaResult<TCtx>` — `{ sagaId; status; stepResults; compensationRecords; startedAt; completedAt; error?; }`.
+- `SagaOptions` — `{ id; name; continueCompensationOnError?; clock?; }`.
+- `Saga<TCtx>` —
+  - `size`, `steps` accessors
+  - `addStep(step)` returns `this`
+  - `execute(context): Promise<SagaResult<TCtx>>`
+- `createSaga<TCtx>(options): Saga<TCtx>`.
+
+## Implementation Notes
+
+The compensator is rebuilt at construction time and `clear()`-ed at the
+start of every `execute`, so the saga is genuinely reusable. The internal
+`extractStepError` helper guarantees that a failed step always surfaces a
+real `Error` instance even if the underlying `StepResult.error` was
+absent — that case is rare (a step that returns `status: "failed"` without
+populating `error` is technically allowed by the type) but the saga has to
+handle it cleanly.
+
+Skipped steps do NOT register a compensation; this preserves the saga
+contract that compensations correspond strictly to side effects that
+happened, not to side effects that were considered.