Core: introduce VTCapabilities

[compnerd]

Introduce the infrastructure to query the terminal what it actually supports. This allows the safe use of advanced features and will allow defaulting to 8-bit encoding if the terminal supports 8-bit encoding rather than the 7-bit encoding.

[Copilot]

Pull Request Overview

This PR introduces the infrastructure to query terminal capabilities through the new VTCapabilities type. This enables safe usage of advanced terminal features by detecting what the terminal actually supports, with fallbacks to basic compatibility when detection fails.

Key changes:

• Added comprehensive terminal capability detection system
• Enhanced input parsing to handle device attribute responses
• Integrated capability querying into the renderer initialization

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
VTCapabilities.swift	Core implementation with enums for terminal types, features, and capability querying logic
VTRenderer.swift	Integration of capability detection during renderer initialization
POSIXTerminal.swift	Updated event mapping to support device attribute responses
VTInputParser.swift	Enhanced parsing for device attribute responses and updated event types
VTEventStream.swift	Documentation update to include response event handling
VTEvent.swift	Added response event type and updated KeyEventType enum

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[Copilot]

[nitpick] The boolean expression can be simplified to return (rawValue & (1 << feature.rawValue)) != 0 which is more idiomatic and clearer.

Suggested change

	return rawValue & (1 << feature.rawValue) == 0 ? false : true
	return (rawValue & (1 << feature.rawValue)) != 0

[Copilot]

The Task.withTimeout API does not exist in Swift's standard library. This appears to be a custom extension that should be documented or the implementation should use standard Swift concurrency patterns like withTaskCancellationHandler and Task.sleep.

Suggested change

	return await capabilities ?? .unknown
	let capabilities: VTCapabilities? = await withTaskGroup(of: VTCapabilities?.self) { group in
	// Task 1: Wait for terminal response
	group.addTask {
	for try await event in terminal.input {
	guard case let .response(response) = event else { continue }
	switch response {
	case let .primary(parameters):
	// The general format of DA1 response is:
	// \u{1b}[<Pt>;<Ps>c
	// Primary Device Attributes (DA1) has two distinct formats that
	// we must handle though.
	// VT100-style: \u{1b}[<terminal-type>;<service-class>c
	if parameters.count == 2,
	let type = parameters.first,
	let type = UInt8(exactly: type),
	let type = VTTerminalType(rawValue: type),
	let service = parameters.last,
	let service = UInt8(exactly: service),
	let service = VTServiceClass(rawValue: service) {
	return VTCapabilities(identity: .specific(type, service))
	}
	// VT220+style: \u{1b}[<terminal-type>;<extensions>c
	if let family = parameters.first,
	let family = UInt8(exactly: family),
	let family = VTTerminalFamily(rawValue: family) {
	let features = parameters.dropFirst()
	.compactMap(UInt8.init(exactly:))
	.compactMap(VTDAFeature.init(rawValue:))
	.compactMap(VTExtensions.init)
	.reduce(into: VTExtensions()) { $0.formUnion($1) }
	return VTCapabilities(identity: .compatible(family, features))
	}
	case .secondary(_), .tertiary(_):
	break
	}
	}
	return nil
	}
	// Task 2: Timeout
	group.addTask {
	try? await Task.sleep(nanoseconds: UInt64(timeout.components.seconds) * 1_000_000_000 +
	UInt64(timeout.components.attoseconds) / 1_000_000_000)
	return nil
	}
	// Return the first non-nil result (i.e., a successful capabilities parse)
	for await result in group {
	if let capabilities = result {
	group.cancelAll()
	return capabilities
	}
	}
	return nil
	}
	await terminal <<< .DeviceAttributes(.Request)
	return capabilities ?? .unknown