cinder chaos: volume/snapshot churn with extend mutations

[berendt]

Closes #32

Summary

Adds a cinder chaos churn/soak mode: it drives volume and snapshot lifecycle churn within a scenario envelope while treating volume extend as a mutation. Rather than fork the Neutron churn engine, this branch first generalizes the shared chaos engine so it names no service, then teaches it a third action class (mutate), and finally maps a Cinder plan onto it and wires up the command.

Change set (in commit order)

1. 3a02cc8 Pin the Neutron churn decision schedule with a golden test
   Captures the exact create/delete/no-op schedule the chaos engine draws for churnPlan() at seed 7 under a virtual clock, generated once with -update. The unchanged bytes become the proof that the subsequent refactor and the new mutate action do not perturb the Neutron decision schedule for a given seed.

2. 3be9c47 Generalize the chaos engine seam and relocate the Neutron builder
   Drops the Neutron interface from the engine's node closures — a Node's Create/Delete now capture their cloud client at graph-build time and operate on the shared resource.Resource, so the engine names no service. Per-operation retry and 404 delete-tolerance move into the builder closures; Config sheds ExternalNetworkID/OpTimeout and gains an optional Classify hook; a create now publishes whatever it returned (with a failed flag) so a created-but-not-ready resource stays deletable and recorded while a doomed child is skipped. The Neutron graph builder, interface, retry wrappers, and error classifier move to a new internal/chaos/neutrongraph subpackage. The golden schedule moves with the tests and stays byte-identical, proving the refactor is invisible for Neutron.

3. 8be83a8 Add a mutate action with a resize_ratio draw to the chaos engine
   Adds a third action class alongside create and delete: a mutation of a live instance (a Cinder volume extend). Each step draws, with probability ResizeRatio, a mutation of a present, not-yet-mutated node carrying a Mutate closure; a node is mutated at most once per lifetime and re-armed when re-created. The draw is double-gated on the graph having mutable nodes and a positive ratio, so a Neutron graph never touches the RNG here and its golden decision schedule stays byte-for-byte identical. Result/ChaosStats gain a Mutates counter (omitempty).

4. 2117368 Add a chaos block with resize_ratio to the Cinder scenario schema
   Gives the Cinder scenario its own chaos block mirroring the Neutron one (duration, interval, parallel, churn_ratio, target_fill) plus the block-storage-specific resize_ratio — the per-tick probability of extending a live, not-yet-resized volume to its planned target. The block is validated (nil-safe, ratios in [0,1], interval min <= max) and duplicated by design so a typo in either service's scenario fails loudly under strict unmarshal. Every shipped profile (5m/30m/1h) gains a chaos block, so cinder chaos --scenario … runs without --duration.

5. be61aaa Add the Cinder churn graph builder
   Maps a Cinder plan onto the chaos engine: one parentless volume node per volume (mutable to its planned resizeToGiB when it has a target) and one snapshot node parented on its source volume, so the engine never snapshots an absent volume nor deletes a volume with live snapshots. Readiness is folded into each operation (create/extend complete only at available, delete only once the resource is gone), and each volume's snapshot/extend/delete operations are serialized behind a per-volume mutex. Drives every call through the cinder executor's retry policy, now exported as WithRetry. Adds one engine guard the cinder graph is first to need: skip a mutation when the create failed (a Cinder create can succeed yet fail readiness — a volume stuck at error — and must stay deletable/recorded but never extended).

6. c6f1de2 Add the cinder chaos command
   Wires the cinder churn graph into a cinder chaos subcommand mirroring neutron chaos: same flag surface and three-layer config merge (defaults < scenario chaos block < flags), plus --volume-type and the block-storage-specific --resize-ratio. It authenticates, resolves the volume type, pre-checks quota against the full plan envelope, builds the cindergraph, runs the churn, records the run with ChaosStats and the volume type, and — unless interrupted or --no-cleanup — tears volumes and snapshots down by metadata (snapshots before volumes, each bounded by --timeout) and runs a leak check. An interrupted or --no-cleanup run prints the cinder cleanup --run-id reclaim hint. buildCinderPlanFromFlags now also returns the scenario so the command can read its chaos block.

7. 839fe45 Document cinder chaos in the README
   Documents the new mode in §15: adds it to the commands block and phase/roadmap status, adds a "Chaos duration" column to the profile table, and adds a "Churn / soak mode (cinder chaos)" subsection covering engine reuse, the volume/snapshot lifecycle, the readiness rule, extend-as-mutation with the new resize_ratio knob (default 0.3, --resize-ratio overrides, 0 disables), the ChaosStats/OTEL outputs, and metadata-based reclamation of an interrupted run.

Divergences from the issue

None visible from the commits: the change implements volume/snapshot churn with extend mutations inside the scenario chaos envelope as issue #32 requested. Note that the branch does more than the literal ask — it first generalizes the shared chaos engine and extracts the Neutron builder into internal/chaos/neutrongraph — but this is enabling refactor, pinned byte-for-byte against a golden decision schedule so Neutron behavior is provably unchanged.

Testing

The diff carries the tests with the code: a golden Neutron decision schedule, generalized engine tests, the new internal/chaos/cindergraph engine/graph tests (lifecycle, envelope, extend-once-per-lifetime, gigabytes bound, per-volume serialization, not-ready and terminal-error paths, schedule determinism), scenario schema validation tests, and command tests mirroring the neutron chaos suite.

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Implemented by planwerk-agent 6b3f3ea with Claude:claude-opus-4-8