refactor(emit): retire legacy backend-collector emitter — target tier never existed

control_plane/src/emit/mod.rs

@@ -7,7 +7,7 @@
 //! | Old path | New path |
 //! |---|---|
 //! | `config/agent.rs` | [`agent`] |
-//! | `config/backend.rs` | [`backend`] |
+//! | `config/backend.rs` | *retired — emitted YAML for a "backend-role" OTel merge collector tier that was never deployed; superseded by the typed L5's [`stage_config::emit_backend_streaming_config_json`] which posts to asapquery-backend's precompute engine over HTTP* |
 //! | `config/asapquery_backend.rs` | [`asapquery_backend`] |
 //! | `config/precompute.rs` | [`precompute`] |
 //! | `config/stage_config.rs` | [`stage_config`] (TODO: split into `opamp` + `streaming_config` + `inference_config` per design.md §5; deferred from refactor 2026-05 because the 3,020-line monolith mixes OTel-collector YAML emit, ASAPQuery-backend JSON emit, and shared internals — clean split needs ownership reorganisation, not file renames) |
@@ -17,7 +17,6 @@
 
 pub mod agent;
 pub mod asapquery_backend;
-pub mod backend;
 pub mod otap;
 pub mod precompute;
 pub mod stage_config;
@@ -26,7 +25,6 @@ pub mod trait_def;
 
 pub use agent::generate_agent_collector_config;
 pub use asapquery_backend::generate_streaming_config_yaml;
-pub use backend::generate_backend_collector_config;
 pub use otap::emit_otap_dag_yaml;
 pub use precompute::{build_precompute_engine_jobs, should_precompute, PrecomputeClient};
 pub use stage_config::{

control_plane/src/emit/stage_config.rs

@@ -22,10 +22,12 @@
 //! These four functions are deliberately **stage-shaped**, not
 //! plan-shaped: the typed L5 emitter has already split the PhysicalExpr
 //! across edge / gateway / backend, so each function only sees the slice
-//! that's relevant to its executor. The legacy emitters in
-//! [`crate::config::agent`] / [`crate::config::backend`] still operate
-//! on the legacy `AgentCollectorConfig` / `BackendCollectorConfig` —
-//! Phase C will gate-flip the demo overlay onto these typed emitters.
+//! that's relevant to its executor. The legacy `agent.rs` emitter still
+//! operates on the flat `AgentCollectorConfig`; the legacy backend
+//! emitter targeted a "backend-role" OTel merge collector tier that was
+//! never deployed and has been retired — typed L5 routes `StageId::Backend`
+//! directly to asapquery-backend's precompute engine over HTTP via
+//! `emit_backend_streaming_config_json`.
 //!
 //! All three are pure transformations: no I/O, no env lookup. The
 //! `opamp_endpoint` parameter is the controller's WebSocket URL the

control_plane/src/main.rs

@@ -34,7 +34,7 @@ use tracing::{info, warn};
 use optimizer::engine::QueryOptimizer;
 use physical::allocator::SketchAllocator;
 use pipeline::{Analyzer, QuerySpec};
-use emit::{generate_agent_collector_config, generate_backend_collector_config, build_precompute_engine_jobs};
+use emit::{generate_agent_collector_config, build_precompute_engine_jobs};
 use workload::WorkloadRegistry;
 use emit::{AgentRuntime, emit_for_runtime};
 use types::AgentCollectorConfig;
@@ -430,7 +430,6 @@ async fn main() {
         .route("/api/v1/agents",                  get(handle_agents))
         .route("/api/v1/config/:metric",          get(handle_get_config))
         .route("/api/v1/collector-config/agent",  get(handle_bootstrap_agent_config))
-        .route("/api/v1/collector-config/backend", get(handle_bootstrap_backend_config))
         .route("/api/v1/cost-model",              get(handle_cost_model))
         .route("/api/v1/tco",                     post(handle_tco))
         .with_state(state)
@@ -504,20 +503,6 @@ async fn handle_plan(
         ).await;
     }
 
-    // ── Push backend config to backend-role collectors ────────────────────────
-    // The typed L5 (`split_typed_three_stage`, below) owns the rich
-    // per-stage backend config now; this legacy push emits the flat
-    // backend YAML from the SP-3 `plan.backend_config`.
-    if let Ok(backend_yaml) = generate_backend_collector_config(
-        &plan.backend_config, &st.opamp_endpoint,
-    ) {
-        let hash = short_hash(&backend_yaml);
-        st.opamp.push_to_role(
-            AgentRole::Backend,
-            RemoteConfig { config_hash: hash, yaml: backend_yaml },
-        ).await;
-    }
-
     // ── Phase B (MVP v6): typed L5 stage_split → per-stage emitter ────────────
     // Behind the `USE_TYPED_STAGE_SPLIT` env-var gate so existing
     // control plane behaviour is unchanged unless explicitly opted in.
@@ -822,11 +807,6 @@ async fn handle_rollback(
                     config_hash: short_hash(&yaml), yaml,
                 }).await;
             }
-            if let Ok(yaml) = generate_backend_collector_config(&plan.backend_config, &st.opamp_endpoint) {
-                st.opamp.push_to_role(AgentRole::Backend, RemoteConfig {
-                    config_hash: short_hash(&yaml), yaml,
-                }).await;
-            }
             (StatusCode::OK, Json(json!({ "metric": metric, "rolled_back": true }))).into_response()
         }
         Err(e) => (StatusCode::BAD_REQUEST, e.to_string()).into_response(),
@@ -1115,24 +1095,6 @@ async fn emit_bootstrap_typed(
         .with_context(|| format!("emit_for_runtime failed for `{metric}`"))
 }
 
-/// Bootstrap YAML config for backend (merge) collectors.
-async fn handle_bootstrap_backend_config(
-    State(st): State<AppState>,
-) -> impl IntoResponse {
-    let cfg = types::BackendCollectorConfig {
-        merge_sketch_type: types::SketchType::DDSketch,
-        group_by:          vec![],
-    };
-    match generate_backend_collector_config(&cfg, &st.opamp_endpoint) {
-        Ok(yaml) => (
-            StatusCode::OK,
-            [("content-type", "application/yaml")],
-            yaml,
-        ).into_response(),
-        Err(e) => (StatusCode::INTERNAL_SERVER_ERROR, e.to_string()).into_response(),
-    }
-}
-
 /// Returns the diff between the current and previous plan for `metric`.
 /// 404 if the metric has no plan, 200 with `null` data if no previous plan exists.
 async fn handle_plan_diff(

control_plane/src/replan.rs

@@ -23,11 +23,11 @@ use tracing::{info, warn};
 use crate::backend_client::{push_or_log, BackendClient};
 use crate::emit::{
     build_precompute_engine_jobs, collect_metric_to_family, emit_for_runtime,
-    extend_edge_with_demo_plumbing, generate_agent_collector_config, generate_backend_collector_config,
+    extend_edge_with_demo_plumbing, generate_agent_collector_config,
     generate_streaming_config_yaml, AgentRuntime, WorkloadRegistry,
 };
 use crate::monitor::Scraper;
-use crate::opamp::{AgentRole, OpampServer, RemoteConfig};
+use crate::opamp::{OpampServer, RemoteConfig};
 use crate::optimizer::baseline::BaselinePlanner;
 use crate::optimizer::{cost as cost_model, rules};
 use crate::physical::stage_split;
@@ -357,18 +357,6 @@ impl Replanner {
                 self.opamp.push(&agent_id, cfg.clone()).await;
             }
         }
-        if let Ok(yaml) = generate_backend_collector_config(&plan.backend_config, &self.opamp_endpoint) {
-            self.opamp
-                .push_to_role(
-                    AgentRole::Backend,
-                    RemoteConfig {
-                        config_hash: short_hash(&yaml),
-                        yaml,
-                    },
-                )
-                .await;
-        }
-
         // Push the ASAPQuery-backend StreamingConfig YAML via HTTP if a
         // backend client is configured. This is the producer side of the
         // ASAPQuery PR E hot-reload contract: the backend receives the