fix(f02-mocks): apply complete f02 validation to write queue (#22)

SetWeightRecords and StepWeightRecords key their slot by op alone and hold
the whole batch as a single entry, so a second batch is rejected while one
is pending even when it names entirely different streams. The three
per-stream ops keep (id, op). A batch applies as one unit.

CancelPending addresses the weight slots with a null id, and rejects the
id/op shape mismatch in both directions.

A queued write walks the pending queue in effective-epoch order, applying each
entry to a candidate projection and validating from its own effective epoch.
Failing entries drop. The call is refused when the write does not survive its
position, or when the walk accepts fewer slots than it did without it.

Due writes are checked again at settle, since a cancellation can take away what
one depended on, and dropped if they no longer hold.

The weight sum is sampled at every breakpoint: clamped linears peak on a kink or
at the limit.

Assisted-by: Claude:claude-sonnet-4-6
Co-authored-by: William Morriss <wjmelements@gmail.com>

Author: wjmelements