[dangreen]

Why

deferScope hands its scope back only when the body returns. A body that throws loses the handle, and what it created before the throw stays linked to the stores it read, with nothing left to stop it. The upcoming @nanoviews/server renders a whole app in a deferred scope and stops it as soon as the markup is written, so a failed request would leave its computeds and effects subscribed to every store that outlives the request. Today it catches the error inside the body to get the handle back, stops the scope and throws the error again.

With createScope the render runs in a scope created under one made beforehand, and stopping that one stops the render either way:

const scope = createScope()

try {
  deferScope(render, scope)
} finally {
  stopScope(scope)
}

What

• agera exports createScope(parent?), and kida and @nano_kit/store re-export it. It is the function deferScope and boundDeferScope already make their scopes with, so a bundle that uses either gets no new code.
• It takes and returns a DeferredScope, the handle the other scope functions work with. The parent of deferScope is a DeferredScope now instead of a ReactiveNode: nothing in this repo or in nanoviews passes one, and the scope functions are @internal.
• Two specs: a scope whose body threw is stopped with the scope it was created under, and a scope from createScope is stopped with its parent.

Size

Entry	Before	After	Limit
agera All publics (Gzip)	3423 B	3430 B	3.45 kB
agera All publics (Brotli)	3157 B	3169 B	3.2 kB
kida All publics (Gzip)	5414 B	5418 B	5.45 kB
kida All publics (Brotli)	5020 B	5022 B	5.05 kB
@nano_kit/store All publics (Gzip)	6846 B	6849 B	6.85 kB
@nano_kit/store All publics (Brotli)	6298 B	6346 B	6.3 → 6.35 kB

Only the name of the export is new. The Brotli size of @nano_kit/store moves by 48 B where its Gzip size moves by 3 B, which is compression noise, but it no longer fits the old limit. Signal, Minimal set and Popular set are unchanged in every package.

Verification

oxlint, tsc --noEmit and vitest are clean in agera. tsc --noEmit passes in kida, @nano_kit/store, @nano_kit/query and @nano_kit/devtools, and size-limit passes in agera, kida and @nano_kit/store.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.60%. Comparing base (aa15c29) to head (5101768).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #309      +/-   ##
==========================================
- Coverage   83.62%   83.60%   -0.03%     
==========================================
  Files         228      228              
  Lines        4849     4849              
  Branches     1074     1074              
==========================================
- Hits         4055     4054       -1     
  Misses        553      553              
- Partials      241      242       +1     

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