pi v0.84.1: Qwen Token Plan Individual, pi auth check, terminating blocked tool calls

v0.84.1, released the day after v0.84.0, is a focused follow-up. The headline addition is a built-in Qwen Token Plan Individual provider whose subscription catalog is documented alongside the existing Qwen entries in the API Keys reference. Individual subscribers can now sign in through /login and use their tier without manually wiring up an API key.

Authentication gets a new diagnostic command: pi auth check verifies that the configured credentials for a provider or model are usable, and can optionally emit the resolved credential to stdout. The command is intended for CI, scripted health checks, and for debugging /login failures without having to start an interactive session.

The fullscreen TUI mode introduced in v0.84.0 gains finer text selection — words and paragraphs can now be selected with multiple clicks — and a configurable half-page scroll for the transcript. Extension authors get a new affordance as well: a tool_call handler can terminate a blocked batch of tool calls without triggering another model call, which is useful when an extension has enough information to short-circuit the loop.

The release also includes the usual set of fixes around session metadata, llama.cpp usage accounting, and Anthropic gateway bearer authentication. Full documentation links are on the GitHub release page.