Allow agent host copilot cli to use selection text and range

[anthonykim1]

Resolves: #314184

After PR:

wires selected text/range through the VS Code -> Agent Host -> Copilot SDK path.
We'd prob eventually want: #314248

/cc @DonJayamanne

[Copilot]

Pull request overview

This PR updates the Agent Host chat path to carry richer attachment data for selections so Copilot CLI requests can preserve selected text and ranges, aligning the Agent Host flow more closely with the existing chat-panel CLI behavior.

Changes:

• Preserve selection text/range when converting chat variables into Agent Host message attachments.
• Translate the new protocol attachment shape through side effects and Copilot session sending.
• Sync generated agent-host protocol types for richer attachments, completions, and response-part variants.

Show a summary per file

File	Description
src/vs/workbench/contrib/chat/test/browser/agentSessions/agentHostChatContribution.test.ts	Updates chat contribution tests for resource-style attachments and selection metadata.
src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostSessionHandler.ts	Converts request variables into richer Agent Host attachments and reads selection text from models.
src/vs/platform/agentHost/test/node/copilotAgentSession.test.ts	Extends Copilot session tests to assert selection text/range forwarding.
src/vs/platform/agentHost/test/node/agentSideEffects.test.ts	Adds coverage for mapping protocol attachment metadata into agent attachments.
src/vs/platform/agentHost/node/protocolServerHandler.ts	Registers the new protocol completions request handler.
src/vs/platform/agentHost/node/copilot/copilotAgentSession.ts	Forwards selection attachment text/range into the Copilot SDK payload.
src/vs/platform/agentHost/node/agentSideEffects.ts	Maps protocol message attachments into IAgentAttachment values for agent backends.
src/vs/platform/agentHost/common/state/sessionState.ts	Re-exports the renamed message attachment enum from protocol state.
src/vs/platform/agentHost/common/state/protocol/state.ts	Syncs generated protocol state for richer attachments, model metadata, and new response-part kinds.
src/vs/platform/agentHost/common/state/protocol/messages.ts	Adds the generated completions command to the protocol message map.
src/vs/platform/agentHost/common/state/protocol/commands.ts	Syncs generated protocol command types for completions and richer initialize data.
src/vs/platform/agentHost/common/state/protocol/.ahp-version	Bumps the synced agent-host protocol version pointer.
src/vs/platform/agentHost/common/agentService.ts	Introduces agent-side attachment enums and selection metadata types.

Copilot's findings

Comments suppressed due to low confidence (1)

src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostSessionHandler.ts:2455

• This has the same worktree mismatch as the earlier location branch: the attachment URI is rebased to the resolved worktree, but the selected text is still read from v.value.uri. When the worktree copy has diverged from the original workspace file, the agent will receive a worktree path paired with stale selection contents from the wrong file revision.

					const attachmentUri = this._rebaseAttachmentUri(uri, request.sessionResource);
					const selectionMetadata = isLocation(v.value) ? await this._readSelectionAttachmentMetadata(v.value.uri, v.value.range) : undefined;

• Files reviewed: 13/13 changed files
• Comments generated: 7