Phase 28-36 body of work

Accumulated since a6f12e2 (Phase 21 Rust port + Phase 27 versioning):

- Phase 36: embed_semaphore on VectorState (permits=1) serializes
  seed embed calls — prevents sidecar socket collisions under
  concurrent /seed stress load
- Phase 31+: run_stress.ts 6-task diverse stress scaffolding;
  run_e2e_rated.ts + orchestrator.ts tightening
- Catalog dedupe cleanup: 16 duplicate manifests removed; canonical
  candidates.parquet (10.5MB -> 76KB) + placements.parquet (1.2MB ->
  11KB) regenerated post-dedupe; fresh manifests for active datasets
- vectord: harness EvalSet refinements (+181), agent portfolio
  rotation + ingest triggers (+158), autotune + rag adjustments
- catalogd/storaged/ingestd/mcp-server: misc tightening
- docs: Phase 28-36 PRD entries + DECISIONS ADR additions;
  control-plane pivot banner added to top of docs/PRD.md (pointing
  at docs/CONTROL_PLANE_PRD.md which lands in next commit)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/catalogd/src/service.rs

@@ -17,11 +17,12 @@ pub fn router(registry: Registry) -> Router {
         .route("/datasets", post(create_dataset))
         .route("/datasets", get(list_datasets))
         .route("/datasets/{id}", get(get_dataset))
-        .route("/datasets/by-name/{name}", get(get_dataset_by_name))
+        .route("/datasets/by-name/{name}", get(get_dataset_by_name).delete(delete_dataset_by_name))
         .route("/datasets/by-name/{name}/metadata", post(update_metadata))
         .route("/datasets/by-name/{name}/resync", post(resync_dataset))
         .route("/resync-missing", post(resync_all_missing))
         .route("/migrate-buckets", post(migrate_buckets))
+        .route("/dedupe", post(dedupe_by_name))
         // Phase D: AI-safe views
         .route("/views", post(create_view).get(list_views))
         .route("/views/{name}", get(get_view).delete(delete_view))
@@ -121,7 +122,14 @@ async fn create_dataset(
             let resp = DatasetResponse::from(&manifest);
             Ok((StatusCode::CREATED, Json(resp)))
         }
-        Err(e) => Err((StatusCode::INTERNAL_SERVER_ERROR, e)),
+        Err(e) => {
+            let status = if e.contains("different schema") {
+                StatusCode::CONFLICT
+            } else {
+                StatusCode::INTERNAL_SERVER_ERROR
+            };
+            Err((status, e))
+        }
     }
 }
 
@@ -153,6 +161,25 @@ async fn get_dataset_by_name(
     }
 }
 
+/// Remove a dataset manifest by name. Metadata only — parquet files,
+/// vector indexes, and tombstones are NOT cascade-deleted. See
+/// `Registry::delete_dataset` for the full scope.
+async fn delete_dataset_by_name(
+    State(registry): State<Registry>,
+    Path(name): Path<String>,
+) -> impl IntoResponse {
+    match registry.delete_dataset(&name).await {
+        Ok(removed) => {
+            let body = serde_json::json!({ "name": name, "manifests_removed": removed });
+            Ok(Json(body))
+        }
+        Err(e) if e.starts_with("dataset not found") => {
+            Err((StatusCode::NOT_FOUND, e))
+        }
+        Err(e) => Err((StatusCode::INTERNAL_SERVER_ERROR, e)),
+    }
+}
+
 async fn update_metadata(
     State(registry): State<Registry>,
     Path(name): Path<String>,
@@ -214,6 +241,12 @@ async fn migrate_buckets(State(registry): State<Registry>) -> impl IntoResponse
     }
 }
 
+/// Collapse duplicate manifests by `name` — see `Registry::dedupe_by_name`.
+/// Safe to run repeatedly; single-manifest datasets are untouched.
+async fn dedupe_by_name(State(registry): State<Registry>) -> impl IntoResponse {
+    Json(registry.dedupe_by_name().await)
+}
+
 // --- Phase D: AI-safe views ---
 
 #[derive(Deserialize)]