Restructure copilot-instructions.md to emphasize mandatory baseline build

[Copilot]

Description

The coding agent was skipping baseline setup steps before building/running tests, causing "missing testhost" and "shared framework" errors. Restructured instructions to make baseline build impossible to miss.

Key changes:

• Moved baseline build to first section after title with ⚠️ MANDATORY heading
• Added explicit cause-effect: skipping causes testhost/shared framework errors
• Replaced verbose bullet lists with quick-scan tables for component ID and build commands
• Added gate condition: "Only proceed after baseline build succeeds"
• Reduced document from ~325 to ~185 lines (~43% reduction)
• Removed table of contents and verbose iterative strategy section (standard behavior, not actionable)
• Consolidated troubleshooting and references into compact table format

Restored guidance per feedback:

• WASM/WASI library detection logic (condensed)
• "Checkout main branch" instruction before baseline build
• Instruction to switch back to working branch after baseline build
• Success criteria (exit code 0, zero test failures)
• Library test project structure guidance with discovery command
• "Target does not exist" troubleshooting entry
• Log collection guidance for failure reporting

Added new components per feedback:

• Added entries for src/tools, src/native/managed, src/tasks, src/tests to component identification table
• Added baseline build commands for Tools, Build Tasks, and Runtime Tests
• Added workflow sections for Tools, Build Tasks, and Runtime Tests with build/test commands

Customer Impact

N/A - Internal tooling instructions only.

Regression

No.

Testing

Documentation-only change. Verified no trailing whitespace per markdown guidelines.

Risk

Low. No code changes. Core guidance retained; only organization and emphasis changed.

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

Original prompt

Our instructions aren't working as well as we'd like. In particular, the coding agent isn't doing the baseline setup steps before it tries building/running tests. Please make whatever changes are needed to make these instructions more effectove. That could include anything from minor tweaks to an overhaul. Please retain the core instructions and guidance; focus on organization, brevity, relevance to copilot, etc

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💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

[stephentoub]

/ba-g markdown only

[Copilot]

Pull request overview

This PR restructures the copilot-instructions.md document to address issues where the coding agent was skipping baseline setup steps, causing "missing testhost" and "shared framework" errors. The restructure moves the baseline build instructions to a prominent first section with mandatory warning emphasis and consolidates the document from ~325 to ~150 lines.

Changes:

• Moved baseline build to first section with "⚠️ MANDATORY" heading and explicit warnings about consequences of skipping
• Replaced verbose bullet lists with scannable tables for component identification and build commands
• Removed table of contents and consolidated iterative strategy, troubleshooting, and reference sections into compact formats

Comments suppressed due to low confidence (2)

.github/copilot-instructions.md:73

• The instruction to switch back to the working branch after the baseline build is missing. After completing the baseline build on main (Step 2) and configuring the environment (Step 3), the agent needs to switch back to the working branch before applying changes. Without this step, the agent would apply changes to the main branch instead of the working branch. Add an instruction at the end of Step 3, e.g., "Then switch back to your working branch before making changes."

**Only proceed with changes after the baseline build succeeds.** If it fails, report the failure and stop.

.github/copilot-instructions.md:79

• The iterative build and test strategy guidance has been removed, including important details about retry attempts (up to 5 attempts for build failures, test build failures, and test failures), how to handle different types of test failures, and when to escalate. This guidance helps the agent know when to retry vs when to report failure. While this might reduce verbosity, it may lead to the agent giving up too early or retrying indefinitely without clear boundaries. Consider adding a brief note about retry strategy, such as: "If builds or tests fail, attempt to fix and retry up to 5 times with different approaches before reporting failure."

After completing the baseline build above, use the appropriate workflow for your changes.

[stephentoub]

@copilot address the feedback please

[Copilot]

@copilot address the feedback please

Addressed all feedback in 98963cc:

• Restored WASM/WASI library detection logic in condensed form
• Added "checkout main branch" instruction before baseline build
• Added instruction to switch back to working branch after baseline build
• Added success criteria (exit code 0, zero test failures) to workflows section
• Added library test project structure guidance with discovery command
• Added "Target does not exist" troubleshooting entry
• Added log collection guidance for failure reporting

[jkoritzinsky]

@copilot please address the feedback in this review.

[Copilot]

@copilot please address the feedback in this review.

Added all requested entries in 4754fd9:

• Component table entries for src/tools, src/native/managed, src/tasks, src/tests
• Baseline build commands for Tools, Build Tasks, and Runtime Tests
• Workflow sections for Tools, Build Tasks, and Runtime Tests with build/test commands

[stephentoub]

/ba-g markdown only