[Anthony Kim (anthonykim1)]

Resolves: #315055

/cc Don Jayamanne (@DonJayamanne) Peng Lyu (@rebornix)

[Copilot]

Pull request overview

This PR improves Copilot CLI’s in-product identity when used via the VS Code chat experience by injecting a VS Code-specific system message into Copilot CLI-backed sessions, ensuring the model doesn’t present itself as a “terminal assistant”.

Changes:

• Add a VS Code-specific systemMessage to agent-host Copilot session configuration (including provisional-session materialization).
• Add a VS Code Copilot CLI chat-panel identity system message to Copilot CLI session options (including when resuming/getting sessions).
• Add unit tests verifying that the system message is passed through in both the agent-host and extension session flows.

Show a summary per file

File	Description
src/vs/platform/agentHost/node/copilot/copilotAgent.ts	Introduces and wires a VS Code-specific system message into the SDK session config builder.
src/vs/platform/agentHost/test/node/copilotAgent.test.ts	Adds coverage that provisional-session materialization forwards the system message to the SDK.
extensions/copilot/src/extension/chatSessions/copilotcli/node/copilotcliSessionService.ts	Always sets a Copilot CLI chat-panel identity system message (optionally prefixed by prompt variable context).
extensions/copilot/src/extension/chatSessions/copilotcli/node/test/copilotCliSessionService.spec.ts	Adds coverage that createSession/getSession pass the identity system message and preserve variable context ordering.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 0

[github-actions]

Base: e4067ee3 Current: 121da83b

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