Automatic V2 Agent Upgrades and ACP Sign-In

This release turns on automatic V2 agent upgrades by default when a V3 session starts and lets ACP clients that declare terminal authentication sign in to Kiro from a terminal. Custom agents built for V2 keep working on V3 without a manual upgrade run, and a capable client opens a terminal sign-in flow. It also draws Mermaid node shapes and nested subgraphs, adds a KIRO_RUNTIME_DIR override for the bundled runtime, and tidies V3 approval prompts. Fixes cover fullscreen scrolling, click targeting in fullscreen, and the Homebrew upgrade hint.

Kiro CLI can upgrade V2-format agents to the V3 format when a V3 session starts. That upgrade now runs unless you turned it off: an unset chat.enableAutoAgentUpgrade preference enables launch migration, while an explicit false stays off. It covers your workspace and global agent directories, or the KIRO_AGENT_CONFIG_DIR directory when set, and rewrites each agent file in place after saving a .json.bak backup. To keep agents in V2, run kiro-cli settings chat.enableAutoAgentUpgrade false; interactive V3 launches then show a notice naming how many agents still need upgrading. Learn more ->

If kiro-cli acp starts while you are signed out, ACP clients that declare terminal authentication now offer a Log in to Kiro method that runs kiro-cli login in a terminal. Complete the sign-in and reconnect, and the agent starts with your credentials. If your client does not declare terminal authentication, Kiro asks you to run kiro-cli login. Until you sign in, every other request returns an authentication-required error. Learn more ->