One PBI, three customizations working together

Watch custom agents pick up instructions and skills while delivering a .NET change. Researched 11 Oct 2026.

← Individual explainers

Azure DevOps · PBI 4521Sprint 42

Orders: support a percentage discount

Legacy.Api · .NET Framework 4.7.2EF6xUnit

Add DiscountPercent (0–50) to Order.
GET /api/orders/{id} returns the discounted total.
Reject discounts over 50% with 400.

Customizations in the repoclick any item

Instructions

copilot-instructions.md

data-access-ef6-adonet.instructions.md

aspnet-webapi-netfx.instructions.md

xunit-tests.instructions.md

wpf-mvvm.instructions.md

Custom agents

dotnet-planner.agent.md

dotnet-implementer.agent.md

xunit-test-writer.agent.md

dotnet-reviewer.agent.md

Skills

pbi-implementation-plan

ef6-add-migration

webapi-endpoint-scaffold

dotnet-test-triage

MCP

Azure DevOps MCP server

Built-in system prompt

dotnet-planner

Plans · read-only

waiting

▶ Start Implementation

dotnet-implementer

Edits · builds · tests

waiting

▶ Review Changes

xunit-test-writer

Subagent · own contextNot used (no subagents in VS)

waiting

dotnet-reviewer

Reviews · read-only

waiting

Workspace files

src/Legacy.Data/Entities/Order.cs—

src/Legacy.Data/Migrations/…_AddOrderDiscount.cs—

src/Legacy.Api/Controllers/OrdersController.cs—

src/Legacy.Api/Services/OrderService.cs—

tests/Legacy.Api.Tests/OrdersControllerTests.cs—

src/Desktop.Wpf/… (untouched)—

Context window of —main chat

context used0

Activitytool calls · loads · results

🧪 What if…changes replay the walkthrough

ef6-add-migration has a vague description ('EF helper')The skill never matches; see what the agent does without it. Remove applyTo from data-access instructionsThe EF6 rules no longer attach when Order.cs is edited. Reviewer agent has no tools: fieldOmitted tools = every tool, including edit. No Azure DevOps MCP server configuredThe planner can't fetch the work item itself. Don't use a subagent for testsImplementer writes and runs tests in its own (growing) context.

Who used what (fills in as you play)

Agent	Instructions	Skills	Tools / MCP
dotnet-planner
dotnet-implementer
xunit-test-writer
dotnet-reviewer

Takeaway: instructions = the rules every agent inherits; agents = who does the work and with which tools; skills = the procedures they pull in only when the task matches.