[2/N Status & List APIs] feat(storage): add request read-model schema (#321)

## Summary
Add gateway request summary entities and SQL tables keyed for sqid,
queue receipt history, and change URI lookup.

## Test Plan
✅ `make fmt && make build && make test && make check-mocks && make
e2e-test`

## Issues


## Stack
1. #314
1. @ #321
1. #322
1. #327

Author: albertywu

submitqueue/entity/BUILD.bazel

@@ -17,6 +17,7 @@ go_library(
         "queue_config.go",
         "request.go",
         "request_log.go",
+        "request_summary.go",
         "speculation_tree.go",
     ],
     importpath = "github.com/uber/submitqueue/submitqueue/entity",

submitqueue/entity/request_summary.go

@@ -0,0 +1,70 @@
+// Copyright (c) 2025 Uber Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package entity
+
+// RequestSummary is the gateway-owned materialized current view of a request.
+// RequestID is exposed as sqid by the gateway API.
+type RequestSummary struct {
+	// RequestID is the globally unique request identifier.
+	RequestID string
+	// Queue is the queue supplied at receipt.
+	Queue string
+	// ChangeURIs are the change URIs supplied at receipt in caller order.
+	ChangeURIs []string
+	// ReceivedAtMs is the immutable receipt timestamp in Unix milliseconds.
+	ReceivedAtMs int64
+	// Status is the current customer-facing request status.
+	Status RequestStatus
+	// RequestVersion is the orchestrator request version carried by the winning log entry, or zero when unavailable.
+	RequestVersion int32
+	// StatusTimestampMs is the timestamp of the winning log entry in Unix milliseconds.
+	StatusTimestampMs int64
+	// Version is the optimistic-lock version of this materialized view.
+	Version int32
+	// LastError is the error associated with the current status, or empty when absent.
+	LastError string
+	// Metadata is display and debugging metadata associated with the current status.
+	Metadata map[string]string
+}
+
+// RequestQueueSummary is the queue-ordered projection returned by List.
+type RequestQueueSummary struct {
+	// RequestID is the globally unique request identifier.
+	RequestID string
+	// Queue is the queue supplied at receipt.
+	Queue string
+	// ChangeURIs are the change URIs supplied at receipt in caller order.
+	ChangeURIs []string
+	// ReceivedAtMs is the immutable receipt timestamp in Unix milliseconds.
+	ReceivedAtMs int64
+	// Status is the current customer-facing request status.
+	Status RequestStatus
+	// Version is copied from the authoritative RequestSummary and guards stale projection writers.
+	Version int32
+	// LastError is the error associated with the current status, or empty when absent.
+	LastError string
+	// Metadata is display and debugging metadata associated with the current status.
+	Metadata map[string]string
+}
+
+// RequestURI maps one change URI to one received request.
+type RequestURI struct {
+	// ChangeURI is the exact canonical URI supplied at receipt.
+	ChangeURI string
+	// ReceivedAtMs is the immutable receipt timestamp in Unix milliseconds.
+	ReceivedAtMs int64
+	// RequestID is the globally unique request identifier.
+	RequestID string
+}

submitqueue/extension/storage/mysql/schema/README.md

@@ -22,3 +22,22 @@ As the `batch` table grows, the secondary index will grow with it, increasing st
 
 The `change` table records per-URI claims by in-flight requests. `request_id` is part of the primary key so that concurrent claims on the same URI by different requests coexist as distinct rows — a same-request retry collides on the PK and is a no-op (`INSERT IGNORE`), while a different-request claim is a new row that `GetByURI` surfaces for overlap detection. `queue` leads the key so queue-scoped lookups are primary-key-prefix scans and the table is shardable by queue.
 
+## Gateway request read model
+
+The gateway request read model uses three additive tables and requires no alteration of existing tables. Deployments create these tables empty and populate them only for requests received after rollout; historical request logs and orchestrator working tables are intentionally not backfilled.
+
+### `request_summary`
+
+`request_summary` is keyed by `request_id` and serves direct Status lookup. It stores immutable receipt context plus the current materialized request-log winner and its optimistic-lock projection version.
+
+### `request_summary_by_queue`
+
+`request_summary_by_queue` is keyed by `(queue, received_at_ms, request_id)`. This key covers the List predicate, descending sort, and keyset continuation for one bounded receipt-time window without a secondary index. The row duplicates the complete List response so one page is served by one range scan rather than one follow-up read per request ID.
+
+### `change_uri_request_mapping`
+
+`change_uri_request_mapping` is keyed by `(change_uri, received_at_ms, request_id)` and serves bounded newest-first Status lookup by change URI. The gateway reads at most 101 mappings to enforce the API maximum of 100 results without silently truncating.
+
+### JSON collections
+
+`change_uris` and `metadata` are non-null application values. MySQL JSON columns can contain the JSON value `null` despite `NOT NULL`, so stores normalize nil slices and maps to empty values on both write and read.

submitqueue/extension/storage/mysql/schema/change_uri_request_mapping.sql

@@ -0,0 +1,6 @@
+CREATE TABLE IF NOT EXISTS change_uri_request_mapping (
+    change_uri VARCHAR(255) NOT NULL,
+    received_at_ms BIGINT NOT NULL,
+    request_id VARCHAR(255) NOT NULL,
+    PRIMARY KEY (change_uri, received_at_ms, request_id)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

submitqueue/extension/storage/mysql/schema/request_summary.sql

@@ -0,0 +1,13 @@
+CREATE TABLE IF NOT EXISTS request_summary (
+    request_id VARCHAR(255) NOT NULL,
+    queue VARCHAR(255) NOT NULL,
+    change_uris JSON NOT NULL,
+    received_at_ms BIGINT NOT NULL,
+    status VARCHAR(64) NOT NULL,
+    request_version INT NOT NULL,
+    status_timestamp_ms BIGINT NOT NULL,
+    version INT NOT NULL,
+    last_error TEXT NOT NULL,
+    metadata JSON NOT NULL,
+    PRIMARY KEY (request_id)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

submitqueue/extension/storage/mysql/schema/request_summary_by_queue.sql

@@ -0,0 +1,11 @@
+CREATE TABLE IF NOT EXISTS request_summary_by_queue (
+    queue VARCHAR(255) NOT NULL,
+    received_at_ms BIGINT NOT NULL,
+    request_id VARCHAR(255) NOT NULL,
+    change_uris JSON NOT NULL,
+    status VARCHAR(64) NOT NULL,
+    version INT NOT NULL,
+    last_error TEXT NOT NULL,
+    metadata JSON NOT NULL,
+    PRIMARY KEY (queue, received_at_ms, request_id)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;