the lane S2 red is a share of routed requests, not a timing flake

[santoshkumarradha]

What happens

TestS2TheDefaultGoesSlowAndTheRouterMoves in internal/lane fails when other
suites run beside it. On a quiet box it passes. 316 consecutive runs in
isolation never reproduced it.

That is exactly the shape the repository says to file rather than rerun.

What the red actually means, which is not what it looks like

The assertion at internal/lane/e2e_test.go:467-468 does NOT divide a measured
time. It divides firstsScripted, a lookup into scriptedFirstWorld
(e2e_test.go:945). The wall figures computed at line 449 are logged and
asserted nowhere.

So the test is not timing-sensitive in the way its name suggests. It asserts a
share of requests that were routed to the good lane after the break.

The margin is a cliff, not a slope. Out of 20 routed requests:

answers from the broken lane	asserted figure
2	about 79%
3	exactly 0.0%

A pass sits ONE request away from that cliff every time it passes. The red means
at least 3 of 20 routed requests reached the broken lane after the break, and
nothing about the failure output says so.

How load gets in

One channel only: the ledger's TTFT: e2eWorld(result.ttft) at
e2e_test.go:931, a measured time multiplied by 100, against a real gap of
8.4ms versus 40ms. Under load the wall p90 moved from 1.0s to 10.4s while the
asserted figure never moved at all, which is why the two look unrelated until
you follow the ledger.

Replication

Run the lane suite with the box under load, for instance a full internal/tui3
run beside it. It is not reliable, which is the point. In isolation it is green
316 times out of 316.

Acceptance

Not "it stops failing". A rerun proves nothing here.

1. The failure output prints the per-request lane sequence and the ledger's
   belief at each step. Today a reader cannot tell 3-of-20 from 10-of-20.
2. A deterministic test that drives the ledger to exactly 2 and exactly 3 broken
   answers and asserts 79% and 0.0%, so the cliff is written down rather than
   discovered.
3. Only then, whatever fix follows.

Not a fix

task/lane-s2-under-load at a41e4abc5 is an unfinished edit from an agent that
died mid-change. It is parked, unmerged, and should not be read as a proposal.