feat(kida,store,query)!: attach tasks to the signals they fill

[dangreen]

The tasks pool made waiting imprecise by construction: waitTasks(pool) drained everything in flight, so a wait captured its neighbours' requests along with its own — measured in the streaming SSR prototype as a header segment ready at 168 ms but written at 318 ms, held by an unrelated request. This reworks tasks to live on the signals they fill, and derives "the tasks of a signal" the way agera derives mount state: never stored, collected by walking the dependency graph on demand.

task($to, taskOrFn) attaches a task to the signal or signals it fills — a task filling two stores attaches to both. waitTasks($of) collects the tasks of the signal and of every signal it depends on and drains them wave by wave, re-collecting after each one, so a task spawned by a task and a dependency linked by a settled value are awaited too. None of it touches mount machinery: tasks on plain signals work, mountable/onStart stay just the convenient way to start them, and a shared signal already in flight is visible to a second reader through its own pool.

In kida the walk doubles one Set as the queue and the visited set (a set iterator visits values appended during iteration), waves ride Promise.all over derived promises that cannot reject, and a pool entry removes itself before any wait wakes up. In @nano_kit/store, dehydrate starts the stores through one computed root and waits exactly them. In @nano_kit/query, baseQuery binds the client's task to the query's $data and mutation binds it to [$data, $error, $loading], so everything a query runs — fetches, retryOnError retries, persistence IO — lands in its own pool, and mutations keep the coverage the shared pool used to give them. The tasks() and ssr() settings are gone: queries track themselves, and hydratable() is the whole SSR setting.

Size pins move down along the chain: kida 4.6 → 4.55 kB brotli (4.95 gzip holds with room to spare), store 6.35 → 6.3 gzip and 5.85 → 5.8 brotli, query 4.7 → 4.65 gzip and 4.3 → 4.25 brotli; the mutations-only set pays 1.7 → 1.75 brotli for the mutation tracking while its gzip pin holds. hasTasks is deliberately not exported yet — its only consumer is the streaming renderer, and it arrives with that package.

Lint, tsc --noEmit, 75 kida, 55 store and 164 query tests, and size-limit across the whole chain are green.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.80%. Comparing base (5b15d22) to head (4430a70).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #222      +/-   ##
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+ Coverage   82.48%   82.80%   +0.31%     
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  Files          99       98       -1     
  Lines        2472     2471       -1     
  Branches      521      523       +2     
==========================================
+ Hits         2039     2046       +7     
+ Misses        322      315       -7     
+ Partials      111      110       -1     

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