Add SetEnvironmentVariable section to IPC protocol specification

[Copilot]

This PR adds the missing documentation for the Process SetEnvironmentVariable command (CommandID 0x03) to the IPC protocol specification at documentation/design-docs/ipc-protocol.md.

Changes Made

• Added SetEnvironmentVariable section with Command Code 0x0403 in the Process Commands section
• Documented input payload: name and value strings for the environment variable
• Documented return payload: int32 hresult indicating success or failure
• Positioned correctly: Placed between ProcessEnvironment (0x0402) and ProcessInfo2 (0x0404) sections
• Followed existing style: Maintained the same documentation format and structure as other Process commands

The documentation is based on the runtime implementation at https://github.com/dotnet/runtime/blob/7a7baaa0342f6b6d196ae19f255903b569f4ca18/src/native/eventpipe/ds-process-protocol.c#L970-L1008

Validation

• ✅ Documentation style matches existing Process commands
• ✅ Command Code, inputs, and outputs accurately reflect the runtime implementation
• ✅ Proper struct syntax using semicolons (C++ convention)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>IPC Protocol Specification missing Process SetEnvironmentVariable section</issue_title>
<issue_description>### Documentation Request

The IPC Protocol specification at documentation/design-docs/ipc-protocol.md notes in the commands overview that the Process CommandSet had a CommandID 0x3 corresponding to SetEnvironmentVariable, but there is no section describing the commandID under the process-commands section. The Process SetEnvironmentVariable command is handled in https://github.com/dotnet/runtime/blob/7a7baaa0342f6b6d196ae19f255903b569f4ca18/src/native/eventpipe/ds-process-protocol.c#L970-L1008</issue_description>

<agent_instructions>Maintain the same style used in describing other CommandSet/CommandIDs.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes IPC Protocol Specification missing Process SetEnvironmentVariable section #5664

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[hoyosjs]

@copilot, please try again

[Copilot]

@copilot, please try again

I've added the missing SetEnvironmentVariable section to the IPC protocol documentation. The documentation includes:

• Command Code 0x0403
• Input payload with name and value strings
• Return payload with int32 hresult
• Proper formatting matching other Process commands

Fixed in commits 3440ac2 and c2f56b2.