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fix(signals): a derived store's write in a lane pass is the lane's derivation (#4478)

* fix(signals): a derived store's write in a lane pass is the lane's derivation

`createStore(d => { d.v = m() })` with `m = createMemo(() => 1 + latest(s))`.
An action writes `s` and stays open: `m` is a verdict reader, so its pass
runs in the action's verdict lane and shows the new value now (F-6, D-25).
The derive reads `m`, so its pass is that lane's work too, but its leaf
writes are plain signal writes: they were staged in the flush, which joined
the action, and the store showed the old value until the action ended. A
memo derived the same way publishes into the lane. The derive's write in a
lane pass now becomes the lane's derivation on the leaf (its value the
lane's, the committed value untouched beneath; the lane's end commits it).

Found by the async-gen rerun on rc.20 (pair E3, rows #2 and #7).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015hPxMkC3jg3Uivh65gvaf2

* chore(size): record the derived-store lane-write fix's sizes over next @ 7135a77a

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015hPxMkC3jg3Uivh65gvaf2

* chore(size): record the derived-store lane-write fix's sizes over next @ e49b0c76

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015hPxMkC3jg3Uivh65gvaf2

* chore(size): the lane-write fix's sizes hold over next @ ab3d2add

Re-measured after merging next @ ab3d2add: the same bytes; the ledger
lines name the new base.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015hPxMkC3jg3Uivh65gvaf2

* fix(signals): gate the derived store's lane-pass write on the lane engine

Store bundles without lanes pay 0 B: createStore and compiled CSR and
hydrating drop their cap raises. The lane bundles re-record.

Co-Authored-By: Claud... (continued)

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