Add acceptsInputOnEnter capability to disable Enter key submission in cloud agent sessions

[Copilot]

The Enter key currently submits prompts in GitHub Copilot coding agent / cloud agent chat sessions, which can lead to accidental submissions during multi-line prompt composition. Only the send button should trigger submission.

Changes

API Extension (vscode.proposed.chatSessionsProvider.d.ts)

• Added acceptsInputOnEnter?: boolean to ChatSessionCapabilities
• Defaults to true (backward compatible)
• When false, Enter key is disabled for input submission

Cloud Agent Configuration (chatSessions.ts)

vscode.chat.registerChatSessionContentProvider(
    CopilotChatSessionsProvider.TYPE,
    copilotSessionsProvider,
    copilotSessionsProvider.chatParticipant,
    { supportsInterruptions: true, acceptsInputOnEnter: false }  // Enter disabled
);

Tests (copilotCloudSessionsProvider.spec.ts)

• Verifies cloud agent sessions set acceptsInputOnEnter: false
• Confirms default behavior for other session types

Scope

Only affects cloud agent sessions. CLI, Claude, and default chat sessions retain Enter key submission.

Original prompt

The enter key should not send a prompt when in the "GitHub Copilot coding agent" / cloud agent chat session provider. Only the send button should do that.

Created from VS Code via the GitHub Pull Request extension.

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[pierceboggan]

The return key on the Copilot coding agent still sends on enter.