feat(stovepipe): Add build issue detection contract (#898)

## Summary
**What**:
- Define provider-neutral discovery of confirmed validation issues
identified by a logical task and optional unit.

**Why**:
- Support deduplicated accumulation of open issues as validation
progresses.

## Test Plan
- [x] Verify the new contract and generated test doubles compile.

## Revert Plan
- Revert this PR. It introduces no runtime wiring, schema changes, or
persisted data.

## Issue Links
- [CODEM-607](https://linear.app/uber/issue/CODEM-607/build-analysis)

Author: prathshenoy

Makefile

@@ -627,6 +627,7 @@ GO_GENERATE_PACKAGES := \
 	./runway/extension/merger/... \
 	./stovepipe/controller/... \
 	./stovepipe/core/requestlog/... \
+	./stovepipe/extension/buildissue/... \
 	./stovepipe/extension/buildrunner/... \
 	./stovepipe/extension/projectstatus/... \
 	./stovepipe/extension/queueconfig/... \

stovepipe/entity/BUILD.bazel

@@ -4,6 +4,7 @@ go_library(
     name = "go_default_library",
     srcs = [
         "build.go",
+        "build_issue.go",
         "ingest.go",
         "list.go",
         "project_status.go",

stovepipe/entity/build_issue.go

@@ -0,0 +1,24 @@
+// 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 entity
+
+// BuildIssue identifies a validation failure by task and optional unit.
+type BuildIssue struct {
+	// TaskID identifies the logical validation task, stable across builds and retries.
+	TaskID string `json:"task_id"`
+	// UnitID identifies the failed unit within the task; empty for a task-wide issue.
+	// Repeated observations of the same condition use the same TaskID and UnitID.
+	UnitID string `json:"unit_id"`
+}

stovepipe/extension/buildissue/BUILD.bazel

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

stovepipe/extension/buildissue/README.md

@@ -0,0 +1,13 @@
+# Build issue detection
+
+`Detector` discovers confirmed validation issues from a build. It returns failure observations, not a complete view of build state.
+
+Issue values are defined in the [domain model](../../entity/build_issue.go). A validation task is a logical validation operation. A validation unit is an identifiable piece of work within a task.
+
+Within a validation queue, TaskID and UnitID together identify the validation condition. Repeated observations of the same condition use the same pair across builds. UnitID is empty for a task-wide issue.
+
+Each detection returns issues discoverable at that time and may repeat earlier observations. Detection does not mark issues as handled. An issue's absence from a detection result does not mean it is resolved.
+
+Detectors must support concurrent calls. Dependency failures return plain errors; issue results returned with an error must not be used.
+
+`Factory` resolves the detector for a validation queue.

stovepipe/extension/buildissue/buildissue.go

@@ -0,0 +1,45 @@
+// 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 buildissue defines confirmed-issue discovery for active or
+// completed builds, independently of build status polling.
+package buildissue
+
+//go:generate mockgen -source=buildissue.go -destination=mock/buildissue_mock.go -package=mock
+
+import (
+	"context"
+
+	"github.com/uber/submitqueue/stovepipe/entity"
+)
+
+// Detector discovers confirmed issues without waiting for build completion.
+// Implementations own confirmation and retry rules and must be concurrency-safe.
+// Detection does not mark issues as handled.
+// An issue's absence from a detection result does not mean it is resolved.
+// Return plain dependency errors; issue results returned with an error must not be used.
+type Detector interface {
+	Detect(ctx context.Context, buildID entity.BuildID) ([]entity.BuildIssue, error)
+}
+
+// Config identifies the queue whose issue detector is requested.
+type Config struct {
+	// QueueName identifies the queue.
+	QueueName string
+}
+
+// Factory resolves a queue's detector; implementations and routing belong to host wiring.
+type Factory interface {
+	For(cfg Config) (Detector, error)
+}

stovepipe/extension/buildissue/mock/BUILD.bazel

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