Codex review findings on the pinned-header change:
1. scrubRequestHeaders flattened a request/header-delta's whole
system/tools payload to one token, so two meaningfully different deltas
compared equal. Now the structural facts survive — keepStart/keepEnd
line positions, added/removed/changed tool NAMES — and only the bulk
(inserted prompt lines, schema bodies) is tokenized.
2. The one-pin design rested on an unasserted premise (all sessions
compose the same header). Every non-pinning scenario now asserts, live,
that each request/header its run produces equals the pinned fixture's
header (both sides normalized against their own volatile values), so a
session-dependent header fails loud until it gets its own pin.
Verified the guard bites: perturbing the pinned fixture's prompt fails
a non-pinned scenario with the intended message.
3. RFC de-slopped per docs/AGENTS.md: no PR reference, no SHOULD
spec-speak; Decision/Verification/Consequences updated for 1 and 2.
Tianyi Cui
a0d8f33b29