Dashboard PKCE login reused the code_verifier as the OAuth state (leaking
it and disabling CSRF validation) and never checked state on callback --
the same class of bug already fixed for the CLI flow. Credential-pool
refresh excluded "anthropic" from the cross-process lock Codex/xAI already
get, so concurrent Hermes processes racing a single-use refresh token could
leave the loser stuck exhausted with no recovery for hermes_pkce/dashboard
sources. The dashboard OAuth save also never cleared a stale
ANTHROPIC_API_KEY, which resolve_anthropic_token() prioritizes over the
OAuth pool entry by design -- so a leftover key silently kept billing
pay-per-token after a Claude Pro/Max login.
A concurrency stress test written to validate the refresh-race fix under
load surfaced a fifth, unrelated bug: _auth_store_lock()'s Windows
lock-file "ensure content" write was unguarded and could raise an uncaught
PermissionError under real contention -- affecting every single-use-token
provider sharing that lock, not just Anthropic.
Fixes#87887, #87888, #87889.
joaomarcos