feat(prose): durability system + docs + MCP server updates

[celom]

Summary

Adds opt-in skip-ahead checkpointing to @celom/prose, complete documentation for the feature, and the MCP server updates needed so AI assistants wired to the server know it exists.

Three commits on this branch:

• febff83 — implementation: DurabilityStore interface, MemoryDurabilityStore reference adapter, checkpoint-after-each-step in the executor, ctx.meta.{runId, idempotencyKey, isResuming}, 17 behavioral tests, and a shared store-conformance suite
• 74615de — docs site: durability guide, order-processing-with-durability example, DurabilityStore API reference, updates to execution-options.mdx / comparison.mdx / types.mdx / index.mdx, both READMEs
• a3b72be — MCP server: DURABILITY_REFERENCE registered as prose://api/durability-store, durability entry in the guides registry, FlowMeta and execute() options updated in api-reference.ts and quick-reference.ts

How it works

After every successful step, the executor persists a checkpoint to the configured store. Re-invoking execute() with the same runId resumes from the next undone step — or replays the saved result if the run already completed. A step may run twice across a crash, so handlers receive ctx.meta.idempotencyKey (${runId}:${stepName}) for external APIs that support deduplication (Stripe, SQS, etc.).

Three observable behaviors of execute() with a durability option:

Stored status	Behavior
no checkpoint	Fresh run — every step executes
running / failed	Resume — completed steps are skipped, state is loaded, execution continues at the first undone step
completed	Replay — saved result is returned without invoking any handler

What this is NOT

Documented in both the guide and the package README. Not a Temporal replacement — no long sleeps that survive process death, no automatic resumer service, no distributed worker claim/lease coordination, no workflow versioning. Just crash recovery for in-process flows, with you bringing the scheduler (cron, queue, next request) when something needs to invoke a resume.

Reviewer notes

• Sidebar orders renumber to fit the new pages (e.g. observability 9→10, types 6→7, user-onboarding 2→3). Not a sidebar redesign — just inserts to keep new pages adjacent to their semantic neighbors.
• MemoryDurabilityStore is marked as test/dev only everywhere it appears.
• The conformance suite at packages/prose/src/lib/__tests__/store-conformance.ts is excluded from the published dist/. Docs direct adapter authors to copy-vendor it or import from source for in-monorepo adapters.
• Tests: 120 passing (17 new durability + 12 new memory-store + existing).

Test plan

• npx nx test prose — 120 passed
• npx nx build prose — clean
• npx nx build docs — 28 pages built
• Manual dev-server pass (npx nx run docs:dev) to skim rendered pages for prose nits
• Spot-check MCP resources (prose://api/durability-store, prose://guides/durability) render in a connected client

Out of scope

• SQLite / Postgres DurabilityStore adapter packages
• CHANGELOG (auto-generated on release)
• Blog post / launch copy

🤖 Generated with Claude Code