Introduce a pure, level-triggered reconciler in `crates/provisioning`
that drives a declared cluster shape toward convergence over the
existing node lifecycle, replacing the edge-triggered imperative node
orchestration in `apps/myelin`.
- `reconcile`/`reconcile_node`/`observe`: pure decider and observation
folder with stable logical-node identity, per-attempt operation
identity, and deterministic retry backoff; `ClusterDriver` is the sole
writer of observed state, coalescing triggers, recording operations as
pending before dispatch, and scheduling timed requeues.
- `IdempotentEffectExecutor`: deduplicates submissions by
`(run_id, logical_node_id, attempt)` and runs provider work on the
engine-hosted blocking substrate, never blocking a reconcile pass.
- Myelin integration: `MyelinEffectBackend` bridges `ProvisionPlugin` to
the executor contract; `LocalProcessPlugin`/`LocalDockerPlugin`
provider adapters; `ProvisionedClusterGuard` pumps triggers,
observations, and due operations.
- Retire the imperative acquire/bootstrap/teardown sequencing across
`apps/myelin` orchestration, staging, observability, and provider
adapters in favor of the declarative driver.
- Move the reconciler specification to `docs/specs/archive`.
Signed-off-by: Zachery Aaron Shores-Chmielewski <zacheryasc@gmail.com>
