docs(flare-workflow): design-spec for saga rollback/compensation handlers

[getappz]

Committed crates/flare-workflow/ROLLBACK_COMPENSATION_DESIGN.md (design doc only, no code changes, per the item's instructions).

Summary of what the doc resolves:

• Data model: reuses StepExecutor<D> (no new trait) — StepDefinition.rollback: Option<Arc<dyn StepExecutor<D>>> + rollback_retry_policy: Option<RetryPolicy>. The forward step's {output} is supplied by reconstructing a fresh WorkflowContext<D> from that step's own journaled StepRun success snapshot (the journal already stores full serialized context, not just a status flag). Rollback is only valid on Sequential/FanOut/Loop steps (the only modes that journal a context snapshot); validate() rejects it elsewhere.
• Durability: new JournalEntry::Rollback variant, same CompletableEntry pattern as everything else, no schema migration — recommended over Cloudflare's own (weaker, undocumented) guarantee because the marginal cost is small and the failure mode of not having it (double-compensation or dropped compensation on crash) is worse.
• Ordering: reverse StepState.started_at (already durable), tied-broken by reverse declaration order — no new monotonic counter needed for v1.
• Trigger: exactly when execute_workflow settles to WorkflowStatus::Failed (both existing settlement points, factored into one finish_workflow_failed helper); ContinueNextStep/RetryIndefinitely/cancellation are explicitly excluded with reasoning, not silently half-supported.
• Rollback's own failures: best-effort per step (extends the existing on_failure-hook precedent), continues unwinding the rest of the saga, reports via new events rather than inflating WorkflowStatus.

Also specifies concrete engine.rs integration (a new src/rollback.rs module mirroring waits.rs's layout) and calls out what's explicitly deferred (JSON-workflow exposure, a RollingBack status, sub-ms ordering) with reasoning for each. Ready for review before any implementation task is scoped.

[coderabbitai]

Warning

Review limit reached

You’ve reached a temporary PR review limit under our Fair Usage Limits Policy.

Your recent review volume is higher than typical usage, so adaptive limits are currently applied.

Next review available in: 54 minutes

Enable usage-based reviews in Billing to review now. Otherwise, wait until the next included review is available.
You're only billed for reviews past your plan's rate limits ($0.25/file).

How can I continue?

After more reviews become available, a review can be triggered using the @coderabbitai review command as a PR comment. Alternatively, push new commits to this PR.

To avoid repeated limits, reduce automatic review volume by pausing incremental auto-reviews earlier, using label-based review opt-in, excluding WIP or generated PR titles, or requesting reviews manually when the PR is ready. If your team needs uninterrupted high-volume reviews, an organization admin can enable usage-based reviews.

How do review limits work?

CodeRabbit enforces per-developer PR review limits for each organization. Most developers receive the normal plan review availability.

For paid Pro and Pro+ PR reviews, CodeRabbit uses adaptive limits for sustained high-volume activity. When a developer's recent PR review activity reaches the 95th percentile or higher among CodeRabbit users, additional reviews become available more gradually as earlier reviews age out of the rolling window.

Please refer docs for additional details.

Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 444cf975-f245-4c08-a9d0-7a33f8ab25c5

📥 Commits

Reviewing files that changed from the base of the PR and between caf5845 and 3610e4d.

📒 Files selected for processing (1)

• crates/flare-workflow/ROLLBACK_COMPENSATION_DESIGN.md

---

_{Comment @coderabbitai help to get the list of available commands.}