feat(planner): (metric, role)-keyed WorkloadStore + PlanStore (B2 full)

[zzylol]

Summary

Closes the B2 deferral from PR #282 — the WorkloadStore and PlanStore are now keyed by (metric: String, role: AggRole) instead of just metric: String. A single metric can carry multiple aggregation roles, each with its own plan, agent assignment, and HTTP plan endpoint.

The bug this fixes: mvp-workload.yaml registers http_requests_total THREE times (entries 2/3/4: sum by (zone), sum by (zone) (rate(...)), count(...)). Pre-B2 the store key was the metric name alone, so set(metric, …) collapsed all three onto one slot — only the LAST entry survived, and sum by (zone) (http_requests_total) PromQL failed at the data plane with ExactAgg(Sum) capability not satisfied.

What changed

• New AggRole enum (Quantile / Sum / Count / Topk / Other) + derive_agg_role() classifier in control_plane/src/workload.rs. Resolution order: (1) sketch_family_override (DDSketch/KLL → Quantile, HLL → Count, CountSketch → Topk, CMS → Other) then (2) outermost PromQL token in query_string.
• WorkloadStore keyed by (String, AggRole) with get_all_for_metric + keys() accessors for emit-path walks.
• PlanStore keyed by (String, AggRole) — rollback / diff / expired all per-pair; metrics() dedups across roles (preserves metrics-exposer wire shape).
• Replanner:
  • agent_to_metric: HashMap<String, String> → agent_to_metrics: HashMap<String, Vec<(String, AggRole)>> so one agent can serve multiple pairs.
  • replan_metric(metric) keeps signature — now a wrapper that loops every role.
  • New replan_metric_role(metric, role) for targeted single-role replans.
  • replan_expired loops over expired pairs; handle_violation re-plans every pair the agent serves.
• main.rs pre-pop loop derives the role per entry via derive_agg_role() — multi-shape metrics now persist as multiple (metric, role) keys.
• handle_plan derives the role from the request's query_string + optional sketch_type override.
• HTTP endpoints (/api/v1/plan/:metric, /diff, /rollback, /config) preserved at metric granularity; responses extended with a per-role roles: [...] array (additive, no breaking URL change). /rollback returns BAD_REQUEST when no role has a previous plan (matches pre-B2 single-role behaviour).
• Emit helpers walk the new keyed store and take the FIRST sketch-binding role per metric for the routing-connector OTTL conditions — Sum-shaped roles correctly decline bind_workload_typed and flow through metrics/raw_passthrough.
• metrics_exposer refresh_plan_ids iterates per-pair; role folded into the plan_id hash so distinct-role plans produce distinct ids.

Ambiguous-case decisions

• count_over_time(...) → Count (cardinality semantics).
• rate / increase / irate → Sum (both bind to ExactAgg(Sum) on the data plane).
• CountMinSketch override → Other (frequency estimator without an inherent topk shape — keeps Topk pure for sketch-with-heap families).

Test plan

• cargo test -p control_plane --lib: 740 pass (was 719; +21 new tests covering AggRole classification, multi-role store coexistence, per-role rollback/diff/expired, multi-role replan, the http_requests_total 3-entry pre-pop loop regression, and the agent-serves-multiple-roles violation handling)
• cargo test -p control_plane --bins: 27 pass (unchanged)
• cargo test -p data_plane --lib: 712 pass (no data_plane edits — backend's ingest_precompute_for_agg_config already handles AggKind::ExactAgg(Sum))
• End-to-end smoke test (/mydata/mvp-smoke-test/run_smoke.sh): NOT run by this PR. Reason: the live deployment's static deploy/configs/backend-streaming.yaml only carries DDSketch entries for http_requests_total — there is no Sum-shaped aggregationType row for the data plane to satisfy sum by (zone). Until either the static YAML is updated OR the dynamic /api/v1/streaming-config POST path is wired up to populate Sum entries from the controller, the smoke test's sumzone query will still surface capability-miss at runtime. The controller change in this PR is necessary but not sufficient for the end-to-end fix; the YAML / dynamic-push follow-up is a separate deployment-config PR.

Links

• PR fix(emit): B3-pop + B4-window bundle (B2-Sum deferred) #282 (the bundle that deferred B2-Sum with note "needs (metric, role)-keyed restructure"): fix(emit): B3-pop + B4-window bundle (B2-Sum deferred) #282
• Original B2 bug: sum by (zone) (http_requests_total) returns {"error":"No result for query"} because the agent never sketches Sum for http_requests_total.

Closes B2.

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