Version 1.5.1

What's Changed

Fixed

• deriveStore(seed, { watched }) never started its watched lifecycle under property-only reads, leaving the store frozen at its seed (src/nodes/store.ts): Previously, only whole-store reads (get(), keys(), iteration) activated the external-push lifecycle; a consumer reading exclusively through store.prop.get(), byKey(), or 'prop' in store activated nothing, so watched never ran — and an external-push Store has no value source other than watched's emit, so it stayed at its seed forever. Now the facade links a dedicated lifecycle anchor from every observation form: a SourceNode that carries watcher edges but never holds or propagates a value. Activation still creates no structural edge, so per-property granularity is unchanged (ADR-0015 clarification). Backported from v2/shape-exploration c48171b.
• List seeds and splice() validated duplicate keys and nullish items inconsistently, and a failing splice() could half-apply (src/nodes/list.ts, src/nodes/collection.ts): Previously, createList(value) and the external-push seed of deriveList did not check for duplicate generated keys — the later item silently replaced the earlier one's signal while keys still listed the key twice, desynchronizing length and get() from the item signals. splice() validated nullish items only where applyChanges() happened to touch them: a content-based keyConfig threw a bare TypeError reading a property of null/undefined, duplicate keys within one inserted batch went undetected (the batch is applied after the loop, so signals.has() never saw the batch's own earlier keys), and an error surfacing mid-mutation left earlier insertions applied. Now the whole batch is staged and validated before anything mutates: nullish items fail validateSignalValue before generateKey, keys are checked against existing signals and the staged batch, an invalid splice() throws with the list unchanged, and seeds throw DuplicateKeyError. Backported from v2/shape-exploration c48171b.

Added

• createCell(value, options?): Alias of createState — the single-value mutable signal, value taken verbatim, no shape conversion. The terminal v2.0 name for the single-value shape under the ADR-0018 Revision (Cell names the single-value shape; Signal stays the umbrella); carried into 2.0 unchanged. Backported from v2/shape-exploration e4408f6.
• deriveCell(input, options?) / DeriveCellOptions<T>: Single-value derive factory with createComputed's dispatch — sync function → Memo, async function → Task — plus the external-push form (seed value + options.watched → Sensor); returns Signal<T>, so origin is not part of the return type. DeriveCellOptions uses the initial vocabulary; initial stays optional and an early read before the first async resolution throws UnsetSignalValueError, exactly as createTask behaves. Terminal bridge for createComputed. Backported from v2/shape-exploration e4408f6.

Deprecated

• deriveSignal(input, options?) / DeriveSignalOptions<T>: Shipped in 1.5.0, deprecated after one release in favor of deriveCell/DeriveCellOptions — a pure rename, same dispatch and options. The ADR-0018 Revision settled that Signal is the umbrella and the single-value shape is Cell, so the 1.5.0 names carry a superseded meaning; both are removed in 2.0. This supersedes the 1.5.0 replacement pointers: createComputed migrates to deriveCell (not deriveSignal), and createMutableSignal migrates to createCell/createList/createStore by argument shape (not createSignal, which 2.0 removes). See MIGRATION-2.0.md "Second flip". Backported from v2/shape-exploration e4408f6.

Changed

• tools/codemod-v2.ts retargeted at the Cell bridge names: createComputed → deriveCell with a literal options.value rewritten to options.initial; deriveSignal → deriveCell and DeriveSignalOptions → DeriveCellOptions as exact-identifier renames; createMutableSignal(v) rewritten by literal argument shape to createCell/createList/createStore — a blanket rename would silently change array and record call sites now that createCell is the narrow single-value factory. createSignal(...) call sites are always flagged, never rewritten (its shape dispatch is removed in 2.0 with no single replacement), and an async createComputed callback is flagged for the Task methods .isPending()/.abort() becoming the free functions isPending(signal)/abort(signal).

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Full Changelog: v1.5.0...v1.5.1