feat(stovepipe): define the repair executor extension

Summary:
Add RepairExecutor.Submit accepting the existing OpenIssue directly. Define
queue-scoped factory resolution and submission acceptance/error semantics,
with generated mocks and Bazel targets. Extensions can resolve additional
context through dependencies injected at construction.

Extract this independently landable contract from the broader design in #893
so provider adapters can implement it before the controller is enabled.

Revert Plan:
Revert this commit.

Author: mnoah1

Makefile

@@ -629,6 +629,7 @@ GO_GENERATE_PACKAGES := \
 	./stovepipe/core/requestlog/... \
 	./stovepipe/extension/buildissue/... \
 	./stovepipe/extension/buildrunner/... \
+	./stovepipe/extension/fixer/... \
 	./stovepipe/extension/projectstatus/... \
 	./stovepipe/extension/queueconfig/... \
 	./stovepipe/extension/sourcecontrol/... \

stovepipe/extension/fixer/BUILD.bazel

@@ -0,0 +1,9 @@
+load("@rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["fixer.go"],
+    importpath = "github.com/uber/submitqueue/stovepipe/extension/fixer",
+    visibility = ["//visibility:public"],
+    deps = ["//stovepipe/entity:go_default_library"],
+)

stovepipe/extension/fixer/README.md

@@ -0,0 +1,11 @@
+# Repair execution
+
+[`RepairExecutor`](fixer.go) submits a repair attempt for an existing [`OpenIssue`](../../entity/open_issue.go). It can invoke an in-process implementation or wrap an external provider. The executor receives the issue directly and can retrieve additional build or failure details through storage dependencies injected at construction.
+
+`OpenIssue.FirstSeenBuildID` identifies the build where this continuous opening of the condition was first observed. Task and unit identifiers retain their existing issue semantics, including an empty unit for a task-wide issue. A provider that cannot repair a given issue returns an error.
+
+`Submit` returns promptly after the provider accepts the attempt, with a nonempty, opaque attempt ID and a nil error. The ID identifies the submitted work; acceptance does not establish that the issue recovered. Build observations remain the source of recovery information.
+
+Each call may start an attempt. The caller owns first-failure selection and duplicate suppression. An error, including a timeout or cancellation, can occur after the provider accepted the work, so it must not cause an automatic resubmission. Implementations return plain dependency errors and must support concurrent calls.
+
+`Factory.For` resolves an executor bound to `Config.QueueName`. Service wiring owns provider selection and injects credentials, clients, and queue mappings into concrete implementations. Generated mocks are available in [`mock`](mock/fixer_mock.go).

stovepipe/extension/fixer/fixer.go

@@ -0,0 +1,44 @@
+// Copyright (c) 2026 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 fixer defines repair submission for a validation issue.
+package fixer
+
+//go:generate mockgen -source=fixer.go -destination=mock/fixer_mock.go -package=mock
+
+import (
+	"context"
+
+	"github.com/uber/submitqueue/stovepipe/entity"
+)
+
+// RepairExecutor submits repair attempts within a configured queue.
+// Implementations must be concurrency-safe and return promptly after submission.
+type RepairExecutor interface {
+	// Submit returns a nonempty, opaque provider attempt ID on acceptance, not recovery.
+	// Repeated calls may start additional attempts. A plain error can follow acceptance,
+	// including on context cancellation; callers must not automatically repeat Submit.
+	Submit(context.Context, entity.OpenIssue) (string, error)
+}
+
+// Config identifies the queue whose repair executor is requested.
+type Config struct {
+	// QueueName identifies the validation queue.
+	QueueName string
+}
+
+// Factory resolves queue-bound executors; routing belongs to service wiring.
+type Factory interface {
+	For(Config) (RepairExecutor, error)
+}

stovepipe/extension/fixer/mock/BUILD.bazel

@@ -0,0 +1,13 @@
+load("@rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["fixer_mock.go"],
+    importpath = "github.com/uber/submitqueue/stovepipe/extension/fixer/mock",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//stovepipe/entity:go_default_library",
+        "//stovepipe/extension/fixer:go_default_library",
+        "@org_uber_go_mock//gomock:go_default_library",
+    ],
+)