(urql) - Fix subscription fetching lifecycle

[zenios]

Summary

Restore the documented useSubscription fetching lifecycle:

• fetching remains true while the subscription source is active, including after payloads
• fetching becomes false when the active source completes
• local React effect cleanup does not masquerade as upstream completion
• results from stale sources cannot update a replacement subscription

Operation results do not carry a React hook fetching field, so computeNextState currently coerces the flag to false on every payload. Conversely, the completion handler uses !!source, but the configured source remains truthy after it has completed, causing completion to report true.

This restores the lifecycle originally discussed in #407 and implemented in #410 while retaining safe source replacement and Strict Mode behavior.

Set of changes

• Track the effect's active source and ignore stale updates
• Apply fetching: true after processing subscription payloads, preserving payload errors
• Set only fetching: false on genuine upstream completion
• Mark local cleanup before unsubscribing so onEnd is not interpreted as remote completion
• Add regression tests for payloads, completion, error preservation, and React Strict Mode cleanup
• Add a patch changeset for urql

This is not a breaking change; it aligns runtime behavior with the existing UseSubscriptionState.fetching documentation.

Validation

• pnpm --filter urql test --run — 59 tests passed
• pnpm --filter urql check
• pnpm --filter urql lint
• pnpm --filter urql build
• pnpm changeset status

[changeset-bot]

🦋 Changeset detected

Latest commit: 6758b0b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
urql	Patch

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