Signals: duplicate dependency links when a signal is written mid-computation (regression in 22.0.2)

Start at the producerAccessed logic in @angular/core/primitives/signals and compare the 22.0.1 and 22.0.2 behavior described in the issue. Run ./run.sh from the linked reproduction, including repro-vue.mjs and repro-effect.mjs, to verify the duplicate-link and over-notification counts. Done means repeated reads remain deduplicated, with two links and one notification for a signal change across the affected versions.

Which @angular/* package(s) are the source of the bug?

core

Is this a regression?

Yes

Description

Since 22.0.2, a reactive consumer that re-reads a signal it already depends on
creates a duplicate dependency link whenever a signal was written in between.
The producer ends up registered several times with the same consumer, so a single
change notifies that consumer several times.

This hits ordinary component templates, because a view is itself a reactive
consumer and both halves of the trigger are supplied by the framework:

• templates read the same signals many times, interleaved, in an order that
  varies with @if / @for;
• Angular writes child component inputs in between
  (applyValueToInputSignal → signalSetFn → producerIncrementEpoch).

So within a single template pass:

read config()          -> link validated at epoch = E
child input binding    -> input write                -> epoch = E+1
read config() again    -> guard fails (E !== E+1)    -> duplicate link

A real template from a component library reads config() 15 times and data()
5 times with child bindings throughout. Reproducing that shape with
@angular/core/primitives/signals (createWatch), and counting the consumer's
producer links plus the consumers registered on each producer:

Angular	links per run	notifications for one config change
21.2.5	2, 2, 2, 2, 2, 2	1
22.0.0	2, 2, 2, 2, 2, 2	1
22.0.1	2, 2, 2, 2, 2, 2	1
22.0.2	11, 11, 11, 11, 11, 11	6
22.1.7	11, 11, 11, 11, 11, 11	6

Expected on all versions: 2 links, 1 notification.

Each extra notification is an extra change detection pass, which re-runs the
view's effects. On a medium-sized application we measured an effect body running
24 times instead of once on first page load, with a very visible startup
slowdown. Restoring the 22.0.1 guard brings it back to 1.

The symptom is limited to the first render, which the mechanism predicts:
signalSetFn increments epoch only when a value actually changes. On first
render every binding goes from undefined to a value, so epoch moves
constantly in the middle of template passes. Once the screen is stable, bindings
stop changing, epoch stops moving mid-pass, and no further duplicates appear.

There is no application-level workaround: neither the repeated reads nor the
input writes are written by the application.

Root cause

producerAccessed deduplicates in three steps. The two fast paths cover only an
immediate re-read of the same producer, and a replay in the same order. The third
path — the one that catches re-reads arriving at a different position — changed in
f902d1d35e
("perf: detect existing signal dependency without checking all producer links"),
released in 22.0.2:

// 22.0.1
... && (!isRecomputing || isValidLink(prevConsumerLink, activeConsumer))

// 22.0.2
... && (!isRecomputing || prevConsumerLink.knownValidAtEpoch === epoch)

epoch is a module-global counter incremented by every signal write. The link
being checked is still valid; it is merely older than an unrelated write. The
optimisation is sound only if epoch advancing implies the link may be stale, and
that does not hold for any computation during which a signal is written — which,
for a view, is the normal case.

Please provide a link to a minimal reproduction of the bug

https://github.com/medi6/angular-regression.git

Please provide the exception or error you saw

No exception — silent over-notification of views, extra change detection passes,
and effects running several times per change.

Please provide the environment you discovered this bug in (run ng version)

Angular CLI 22.1.8, Angular 22.1.7, Node 22.16.0, TypeScript 6.0.3, zone.js-based change detection.

Anything else?

Reproduction with the repo :

repro-vue.mjs (view-shaped consumer) and repro-effect.mjs (effect writing a
signal). No DOM, no browser, no test runner — only @angular/core/primitives/signals.
./run.sh installs each Angular version side by side and prints the table above.