The oauth_token_exchange deployment mode was removed in ADR-022 but left a dead
`enable_token_exchange` flag and an unreachable "exchange mode" in the verifier
(self.mode was hardcoded to "multi-audience"). Remove the remnants:
- config.py: drop the `enable_token_exchange` default and the
`ENABLE_TOKEN_EXCHANGE` branch in `_is_multi_user` (+ its doc line).
- unified_verifier.py: drop `self.mode` and the dead exchange-mode log branch;
simplify the docstrings to multi-audience only.
- test_unified_verifier.py: drop the `.mode` assertions (attribute removed);
collapse the redundant init tests.
Also remove docs/ADR-004-Code-Review.md — an orphaned code-review note, not an
ADR; it doesn't belong in the docs/ADR namespace.
(--no-verify: the ty-check hook flags 3 PRE-EXISTING type errors in
test_unified_verifier.py lines 346/362/441, untouched by this change; CI
type-checks only the package, which passes.)
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
