From 2c6e2a4872a3474961082770f8d5ec8b622d5db5 Mon Sep 17 00:00:00 2001
From: zz_y <zeyingz@umd.edu>
Date: Fri, 15 May 2026 14:38:05 -0600
Subject: [PATCH] refactor(emit): drop aggregationId from readouts wire (PR 5
 alignment)
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Mirror of #244's aggregation-side cleanup, now for readouts. The
backend's `StreamingConfig::from_yaml_data` doesn't consume the
`readouts` list at all today, so this is wire-shape hygiene rather
than a fix — but it keeps the controller's emit consistent with the
content-addressing convention PR 5 established: no controller-allocated
string IDs on the wire.

When the backend eventually starts consuming readouts, the cross-
reference from a readout to its source aggregation will be content-
shaped (metric / sketch_kind / params) — derivable from the
`aggregations` list by the same `PolicyFingerprint` recipe. The
`BackendReadout.aggregation_id` struct field stays in source as
emit-time bookkeeping (populated by `resolve_descendant_agg_id_via_edges`
during the DAG walk; not consumed by anything downstream today).

Touches:
- `build_backend_readout_json`: 4 match arms each drop their
  `aggregationId` key. Doc-comment expanded to explain the
  content-addressing convention.
- `phase_b_backend_json_aggregation_readout_alias_snapshot`: flips
  the readouts assertion from "aggregationId present" → "absent".

Build clean. 687 lib + 27 binary tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 control_plane/src/emit/stage_config.rs | 32 ++++++++++++++++----------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/control_plane/src/emit/stage_config.rs b/control_plane/src/emit/stage_config.rs
index a5925e48..3cd83d82 100644
--- a/control_plane/src/emit/stage_config.rs
+++ b/control_plane/src/emit/stage_config.rs
@@ -1408,24 +1408,29 @@ fn build_backend_aggregation_json(agg: &BackendAggregation) -> JsonValue {
 }
 
 /// Build one readout row in the backend streaming-config JSON.
+///
+/// `aggregation_id` is **intentionally omitted** — PR 5's content-
+/// addressing convention applies to readouts the same way it applies
+/// to aggregations (the controller-allocated string IDs are not on
+/// the wire). The backend's current `StreamingConfig::from_yaml_data`
+/// doesn't consume the `readouts` list at all; when it eventually
+/// does, the cross-reference to its source aggregation will be
+/// content-shaped (metric / sketch_kind / params), derived from the
+/// `aggregations` list by the same `PolicyFingerprint` recipe.
 fn build_backend_readout_json(r: &BackendReadout) -> JsonValue {
     match &r.op {
         EstimateOp::Quantile { q } => json!({
-            "aggregationId": r.aggregation_id,
             "op": "quantile",
             "q": q,
         }),
         EstimateOp::Cardinality => json!({
-            "aggregationId": r.aggregation_id,
             "op": "cardinality",
         }),
         EstimateOp::PointCount { key } => json!({
-            "aggregationId": r.aggregation_id,
             "op": "point_count",
             "key": key,
         }),
         EstimateOp::TopK { k } => json!({
-            "aggregationId": r.aggregation_id,
             "op": "topk",
             "k": k,
         }),
@@ -2298,19 +2303,22 @@ mod tests {
             }],
         };
         let v = emit_backend_streaming_config_json(&cfg).expect("emit ok");
-        // PR 5: `aggregationId` is no longer on the aggregation side — the
-        // backend derives identity from content (`PolicyFingerprint(u64)`
-        // over metric, sketch_kind, params, grouping, spatial_filter).
-        // Readouts still surface `aggregationId` because the backend's
-        // readout consumption path is unchanged (cleanup deferred — the
-        // current backend's `StreamingConfig::from_yaml_data` ignores the
-        // readouts list entirely, so this string is informational only).
+        // PR 5: `aggregationId` is no longer on the wire — neither on
+        // aggregations nor readouts. Identity on the aggregation side is
+        // content-derived (`PolicyFingerprint(u64)` over metric,
+        // sketch_kind, params, grouping, spatial_filter); the readout-
+        // to-aggregation cross-reference will be content-shaped too when
+        // the backend starts consuming `readouts` (today it's silently
+        // dropped by `StreamingConfig::from_yaml_data`).
         assert!(
             v["aggregations"][0].get("aggregationId").is_none(),
             "controller must not emit aggregationId on aggregations\n{v}"
         );
+        assert!(
+            v["readouts"][0].get("aggregationId").is_none(),
+            "controller must not emit aggregationId on readouts\n{v}"
+        );
         assert_eq!(v["aggregations"][0]["metric"], "phase_b_metric");
-        assert_eq!(v["readouts"][0]["aggregationId"], "phase_b_agg0");
         assert_eq!(v["aggregations"][0]["aggregationType"], "DatasketchesKLL");
         assert_eq!(v["aggregations"][0]["parameters"]["k"], 200);
         assert_eq!(v["readouts"][0]["op"], "quantile");