docs: reorganize data-plane and backend design by ownership

README.md

@@ -130,7 +130,7 @@ spin up ASAPCollector + ASAPQuery-backend + Grafana together — live in
 [ASAPCollector](https://github.com/ProjectASAP/ASAPCollector). The
 full multi-stage MVP demo (10 producers / 2 agents / 1 gateway / 1
 backend / Thanos store-gateway / MinIO) is documented in its
-[`docs/mvp-demo-runbook.md`](https://github.com/ProjectASAP/ASAPCollector/blob/main/docs/mvp-demo-runbook.md).
+[`mvp-demo-runbook.md`](https://github.com/ProjectASAP/ASAPCollector/blob/main/docs/user_guide/mvp-demo-runbook.md).
 
 To build and run just this backend, see **Building from source** below.
 
@@ -192,7 +192,7 @@ backend surfaces in every response's `infos` field.
 The wire format is documented in
 [`asap_otel_proto`](crates/asap_otel_proto/) and
 the cross-language byte-parity gate is described in
-[ASAPCollector's edge-framework design](https://github.com/ProjectASAP/ASAPCollector/blob/main/docs/design-asap-edge-framework.md).
+[ASAPCollector's system design](https://github.com/ProjectASAP/ASAPCollector/blob/main/docs/design_docs/system-overview.md).
 
 ## Query response shape
 
@@ -231,9 +231,9 @@ that produced the current architecture:
 - **Sketch placement planner** — moved into [`ASAPCollector/controller/`](https://github.com/ProjectASAP/ASAPCollector/tree/main/controller)
 - **PromQL pattern matchers for the planner** — migrated into the
   controller's L3 `intent_algebra` + L4 `sketch_algebra`
-- **JSONL cold-fallback path** — deleted; the archive tier replaces
-  it. See ASAPCollector's
-  [`docs/design-jsonl-deprecation-and-gorilla-promql-completeness.md`](https://github.com/ProjectASAP/ASAPCollector/blob/main/docs/design-jsonl-deprecation-and-gorilla-promql-completeness.md)
+- **JSONL cold-fallback path** — deleted; the configured exact backend is the
+  explicit fallback described by
+  [`query-execution.md`](data_plane/docs/design_docs/query-execution.md).
 - **`StorageBackend::ColdJsonlFallback`** enum variant — removed
 - **Backend-local cost-model line item for cold-tier scan bytes** —
   removed (controller's tier-spanning cost model is the source of

data_plane/docs/README.md

@@ -1,114 +1,40 @@
-# QueryEngineRust Developer Documentation
+# ASAPQuery data-plane documentation
 
-Welcome to the QueryEngineRust developer documentation! This directory contains guides for extending the system with new components.
+The data plane ingests state produced under an active BackendPlan, stores that
+state, answers supported PromQL queries, and uses an explicit exact fallback
+for unsupported queries. It executes plans; it does not choose summary families
+or re-plan queries.
 
-## Architecture Overview
+## Design documents
 
-QueryEngineRust is organized into clear, extensible layers:
+- [Plan-aware query execution](design_docs/query-execution.md) — ingestion,
+  routing, readiness, summary readout, and exact fallback contracts.
+- [Repository-wide summary storage](../../docs/design_docs/summary-storage.md) —
+  materialization state, lifecycle, and query consistency.
+- [BackendPlan](../../control_plane/docs/backend-plan.md) — the control-plane
+  contract installed by the data plane.
 
-```
-┌─────────────────────────────────────────────────────────┐
-│                   Client Applications                    │
-└─────────────────────────────────────────────────────────┘
-                           │
-                           ▼
-┌─────────────────────────────────────────────────────────┐
-│              Protocol Servers (HTTP, etc.)               │
-│  - Parse protocol-specific requests                      │
-│  - Route to appropriate adapter                          │
-│  - Handle protocol-specific endpoints                    │
-└─────────────────────────────────────────────────────────┘
-                           │
-                           ▼
-┌─────────────────────────────────────────────────────────┐
-│         Protocol Adapters (Prometheus, etc.)             │
-│  - Parse query language (PromQL, SQL, etc.)             │
-│  - Format responses for protocol                         │
-│  - Determine if query is supported                       │
-└─────────────────────────────────────────────────────────┘
-                           │
-                    ┌──────┴──────┐
-                    ▼             ▼
-        ┌─────────────────┐   ┌──────────────────┐
-        │  Query Engine   │   │ Fallback Client  │
-        │  - Execute      │   │  - Forward       │
-        │    queries      │   │    unsupported   │
-        │  - Return       │   │    queries       │
-        │    results      │   │                  │
-        └────────┬────────┘   └──────────────────┘
-                 │
-                 ▼
-        ┌─────────────────┐
-        │     Store       │
-        │  - Data storage │
-        │  - Sketches     │
-        └─────────────────┘
-                 ▲
-                 │
-        ┌────────┴────────┐
-        │ Ingest Drivers  │
-        │  - Kafka, etc.  │
-        └─────────────────┘
-```
+## Developer documentation
 
-## Directory Structure
+- [Extension boundaries](developer_docs/extension-points.md) — responsibilities
+  of protocol servers, adapters, and fallback clients.
+- [Adding a summary family](../../docs/developer_docs/adding-summary-family.md) —
+  cross-repository prerequisites and backend validation.
 
-```
-src/drivers/
-├── ingest/           # Data ingestion (Kafka, etc.)
-├── query/
-│   ├── adapters/     # Protocol adapters (Prometheus HTTP, etc.)
-│   ├── fallback/     # Fallback backends (Prometheus, ClickHouse, etc.)
-│   └── servers/      # Protocol servers (HTTP, Flight SQL, etc.)
-```
+## User guide
 
-## Extension Guides
+- [Querying ASAP](user_guide/querying-asap.md) — PromQL behavior, planned
+  summary execution, exact fallback, freshness, and errors.
 
-- **[Adding a Protocol Adapter](./adding-protocol-adapter.md)** - Add support for new query protocols (e.g., ClickHouse HTTP API)
-- **[Adding a Fallback Backend](./adding-fallback-backend.md)** - Add new fallback query backends (e.g., DuckDB, Elasticsearch)
-- **[Adding a Protocol Server](./adding-protocol-server.md)** - Add new protocol servers (e.g., Flight SQL, gRPC)
+## Ownership
 
-## Key Concepts
+- [ASAPPlanner](https://github.com/ProjectASAP/ASAPPlanner) owns logical query
+  planning, query-to-summary mapping, and accuracy reasoning.
+- The ASAPQuery control plane owns physical compilation and BackendPlan.
+- The data plane owns ingestion, storage, readout, query execution, and exact
+  fallback under the installed plan.
+- [ASAPCollector](https://github.com/ProjectASAP/ASAPCollector) owns summary
+  construction and transmission at the edge.
 
-### Protocol Adapter
-Handles protocol-specific request/response formatting and query parsing. Examples: Prometheus HTTP API, ClickHouse HTTP API.
-
-### Fallback Backend
-External query system to forward unsupported queries to. Examples: Prometheus, ClickHouse, DuckDB.
-
-### Protocol Server
-Handles network communication for a specific protocol. Examples: HTTP server, Flight SQL server.
-
-## Quick Reference
-
-### Adding a Protocol Adapter
-1. Create `src/drivers/query/adapters/my_adapter.rs`
-2. Implement `HttpProtocolAdapter` trait
-3. Add to factory in `factory.rs`
-4. Update `QueryProtocol` enum
-
-### Adding a Fallback Backend
-1. Create `src/drivers/query/fallback/my_backend.rs`
-2. Implement `FallbackClient` trait
-3. Export from `fallback/mod.rs`
-
-### Adding a Protocol Server
-1. Create `src/drivers/query/servers/my_server.rs`
-2. Implement server logic with appropriate adapter
-3. Export from `servers/mod.rs`
-
-## Testing
-
-Each component should include:
-- Unit tests in the same file
-- Integration tests in `src/tests/`
-- Example usage in documentation
-
-## Contributing
-
-When adding new components:
-1. Follow existing naming conventions
-2. Add comprehensive documentation
-3. Include tests
-4. Update this documentation
-5. Keep backward compatibility
+Historical ingestion paths, file-by-file migrations, and configuration
+walkthroughs are not data-plane design contracts.