Squash of PR #662. The header plan-usage chip gains a Copilot row: the
calendar-month premium-request quota, with the request counts and the
reset in the tooltip, read every 10 minutes from GitHub's
copilot_internal/user endpoint with the Copilot CLI's own sign-in token.
It rides showPlanUsageLimits and is on by default while the CLI is
installed and signed in; any failure leaves the chip without the row.
Merge-time fixes by the maintainer: the gates (setting, then token, then
the CLI probe) live in readCopilotPlanUsageIfEnabled() so a host with no
Copilot sign-in never runs the login-shell probe each tick, with a test
that Plan Usage Limits off means no request; the X-GitHub-Api-Version
header the Copilot CLI itself does not send is dropped; and CLAUDE.md,
architecture-invariants, README and copilot-integration describe the read.
The hooks-config import in server.ts was merged with #666's.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
