feat(providers): add GitHub Copilot CLI

[atarantino]

Summary

Adds GitHub Copilot CLI as a first-class provider backed by its ACP stdio interface, allowing users to use their existing Copilot authentication directly in T3.

This is a stacked draft targeting the head branch of #2829 (t3code/codex-turn-mapping); it can be retargeted to main after that PR lands.

• adds an Orchestrator V2 ACP adapter with streaming, approval handling, model selection, session configuration, and resume support
• discovers Copilot availability, authentication status, CLI version, and account-specific models
• adds ACP-backed text generation for Git metadata and thread titles
• registers Copilot across provider settings, contracts, web, mobile, icons, and documentation
• marks the provider Early Access while Copilot's ACP support remains in public preview

Validation

• focused Copilot ACP, provider, driver, Orchestrator V2 adapter, text-generation, registry, and settings tests passed
• server, web, contracts, and mobile typechecks passed
• formatting and staged-file checks passed
• manual smoke test passed for a read-only prompt and an approval-gated file creation using the auto model

Generated with GPT-5.6 Sol in Cursor.

Made with Cursor

Note

Add GitHub Copilot as a built-in provider with ACP, text generation, and status checks

• Registers GitHub Copilot as a built-in provider driver (CopilotDriver.ts) with its own settings schema (enabled, binaryPath, customModels), health check, snapshot management, and enrichment.
• Adds a Copilot-specific ACP adapter (CopilotAdapterV2.ts) that locks sessions to agent mode, disables proposed-plan emission, and configures model and reasoning_effort via applyCopilotSessionConfiguration.
• Implements a Copilot-backed text generation service (CopilotTextGeneration.ts) that runs ACP prompt roundtrips with a 180s timeout, collects streamed chunks, and decodes structured JSON for commit messages, PR content, branch names, and thread titles.
• Provider status is determined by running copilot --version then discovering models via an ACP session; the resulting snapshot encodes version, auth status, readiness, and available models.
• Exposes the provider in the web UI with an 'Early Access' badge and removes GitHub Copilot from the 'Coming Soon' list; adds a mobile icon and updates docs and README.

📊 Macroscope summarized 78b2f4b. 21 files reviewed, 0 issues evaluated, 0 issues filtered, 0 comments posted

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[macroscopeapp]

One convention finding in the new Copilot service code: a detail attribute derived from cause.message. Everything else (namespace subpath imports, Foo["Service"] usage, environment-based dependency acquisition in the driver/adapter create effects, Effect.catchTags on known tags) follows the service conventions.

^{Posted via Macroscope — Effect Service Conventions}