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fix(signals): a memo's lane pass parks a lane frame, not a transaction zombie (#3698) (#3703)

Fixes #3698. Same root cause and fix independently found by @brenelz in #3699.

A <Show> over an optimistic value held an unrelated synchronous write for
the lifetime of the action that wrote the optimism. The compiler emits a
memo inside Show's `when` getter, so the condition memo owns children; a
lane pass over it parked the previous children as a #3404 transaction
zombie, which queued and stamped the memo as the action's pending node, and
its next mainline recompute re-entered the hold — against the #3460 ruling
that a lane never holds a sync write.

Fix: `recompute`'s parking gate `isEffect && lane` -> `lane`. A memo's lane
pass parks a lane frame like an effect's (CONFIG_LANE_FRAME), retired when
the lane applies — at once for a lane that is not held, at the release for
one that is — and the memo is neither queued nor stamped for the action's
commit.

Ruling (maintainer, 2026-09-28): zombies are transaction work only. A pass
is mainline, transaction or lane work by who owns it, never by node kind,
and the children it replaces retire when the pass's own result reaches the
screen. Recorded as A15 "Lane work and transaction work"; supersedes
#3662's effect-only scope, #3404 unchanged for transaction work.

Tests: 6 signals tests (one ported from #3699), 2 web specs. Size: -3 B
minified; brotli layout -54..+37 B, two frozen caps raised under a
Size-Exception (hydrating no-stores 19.68 -> 19.69 KB, live page
49.07 -> 49.10 KB).

Co-authored-by: Brenley Dueck <brenleydueck@gmail.com>
Co-authored-by: Claude via Cursor <noreply@cursor.com>

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