Login writes access/refresh tokens (and often client_secret) to
tokens.json at mode 0600. Without a gitignore entry, git add . after a
local login can stage live Agentic credentials.
Closes: #20
Outsiders reading this module should not see private sibling
names (tradey), unfinished rewire notes, or /fast/projects
lab paths. Keep the library self-contained in README, design,
plan, and test fixtures/identity strings.