Agent: apply controller's OpAMP-pushed RemoteConfig at runtime (real fix for #381 workaround)

[zzylol]

Goal

Make the OTel agent apply the controller's OpAMP-pushed RemoteConfig at runtime, so the agent's effective pipeline is the controller's per-query-tailored stage-split — not a static placeholder.

Why this is still open (re #381)

#381 documented the gap ("agent never APPLIES the OpAMP RemoteConfig push at runtime") and is closed — but it was closed via PR #350's workaround, not the real fix: the static bootstrap YAML (deploy/mvp-{singlenode,multinode}/configs/asap/asap-otel-agent-b6-asap-single-sketch.yaml) was hand-shaped to match the controller's full 5-sketch routing-connector output so the demo runs "even without OpAMP-push." The header still says so verbatim. So the agent runs a static, all-5-family config regardless of the query workload; the controller emits a correct typed plan that is never engaged.

Confirmed again in the 2026-05 #46 sweep: the agent ran the static all-5 routing-connector config; /api/v1/collector-config/agent shows the controller's tailored YAML, but the effective pipeline is the static one.

Why it matters

• Criterion ② of MVP demo: test-first validation of ASAPCollector + ASAPQuery-backend #46 ("sketches + delta + stage placement determined by the controller based on the query workload") can't be truly demonstrated while the agent ignores the push — it's faked by the static file matching.
• Resource efficiency: the static config instantiates all 5 sketch pipelines even when the workload needs one. Idle families cost ~0 CPU/state (the routing connector feeds each metric to exactly one family), but they are scaffolding + an over-broad config. A controller-tailored config would instantiate only the needed families.
• It blocks controller-emitted changes (e.g. edge-aggregation plans, family selection, delta-transmission toggles) from taking runtime effect without a manual static-config edit.

Acceptance criteria

• Agent receives an OpAMP RemoteConfig from the controller and reloads its collector pipeline to match it (OpAMP effective_config == the pushed config).
• With a latency-only workload, the agent's effective pipeline contains only the planned family (e.g. ddsketch) — no KLL/HLL/countsketch/countmin pipelines instantiated — verifiable via processor metrics / effective-config preview.
• Changing the controller's workload input changes the agent pipeline shape without editing the static bootstrap YAML.
• The static placeholder is reduced to a minimal bootstrap (receivers + OpAMP extension), with families/processors supplied by the push.

References

• MVP demo: agent doesn't apply OpAMP-pushed runtime config (PR #350 residual) #381 (closed via PR fix: archive tier covers all 5 sketched metrics (HLL/CS/CMS/KLL/DDSketch all in Thanos) #350 static-placeholder workaround) — original gap.
• PR fix: archive tier covers all 5 sketched metrics (HLL/CS/CMS/KLL/DDSketch all in Thanos) #350 — emitted the typed 5-sketch routing-connector YAML + made the static placeholder match it.
• Controller emitter: controller/src/config/stage_config.rs::emit_edge_yaml_5sketch_routing.