E2E_FIXTURE_MODE selects the transport every e2e client is built on: live
(default, unchanged behavior), record (pass through to the live proxy while
writing every interaction to a fixture bundle), or replay (serve every
interaction from the bundle with no proxy and no provider spend). Both new
transports fulfil the existing Transport protocol, so no test changes shape.
A bundle is a directory with a manifest (record timestamp, harness version,
format version) and one JSON file per interaction, grouped per test in call
order. Replay against a manifest older than seven days hard-fails at
collection time naming the bundle age. Record always wipes and never reads
the previous bundle, refusing to wipe a directory that is not a bundle.
Auth header values are redacted on write; uploads store a sha256 digest.
unique_marker() becomes deterministic per test in record/replay modes so a
replay run regenerates exactly the requests the record run sent.
Content-based match keys, streaming chunk fidelity, and provider-scoping are
follow-ups (LIT-5741, LIT-5742, LIT-5745).
