test_anthropic_hooks_do_not_break_extract_user_query_lookup mocks
pipeline.apply to return tokens_after=40 and a tiny compressed
message. The pre-Bug-3 proxy trusted the mock's tokens_after and
emitted x-headroom-tokens-after: 40. After issue #327 Bug 3 the
proxy recounts optimized_tokens from result.messages with its
own tokenizer (the mocked "compressed" string counts to 11), so the
header asserted against the wrong tokenizer's number.
Compute the expected value from the same tokenizer the proxy uses
(get_tokenizer("claude-sonnet-4-6")) and assert the recounted
header matches that. Add a tokens_before > tokens_after invariant
so the spirit of the test (compression actually reduced bytes) is
preserved without coupling to a specific tokenizer's calibration.
