fix(useController): reflect cleared parent object in controlled fields (#13550)

[EduardF1]

Fixes #13550

Problem

When a parent object field is replaced wholesale via setValue (for example setting data to null when there are controlled fields on data.type), the controlled fields kept their stale value and went out of sync with getValues() / useWatch.

Root cause

useController subscribes through useWatch with exact: true. In shouldSubscribeByName, exact matching only accepted strict name equality (currentName === signalName). setValue('data', null) emits a change with name: 'data', which never matches the child subscription data.type, so the controlled field was never notified and never re-rendered.

This is also why useWatch (which defaults to exact: false) reflected the cleared value while useController did not — exactly the mismatch reported in the issue.

Fix

In exact mode, also notify a subscriber when the changed (signal) name is a path ancestor of the subscribed name:

exact
  ? currentName === signalName || currentName.startsWith(signalName + '.')
  : currentName.startsWith(signalName) || signalName.startsWith(currentName)

The + '.' boundary keeps siblings and substring-only names from matching (e.g. data does not match database, and data.other does not match data.type). Descendant-only signals are still excluded under exact matching, preserving the documented purpose of exact.

Validation

• New integration test in useController.test.tsx: after setValue('data', { type: 'foo' }) then setValue('data', null), the controlled value becomes undefined and stays in sync with useWatch.
• New unit cases in shouldSubscribeByName.test.ts covering ancestor matches and the sibling/substring exclusions (data vs database).
• pnpm test (full suite): 1182 passed.
• Targeted: shouldSubscribeByName, useController, useWatch, controller, setValue, useFormState — all green.
• eslint clean on changed files; tsc --noEmit passes.

Not a duplicate

There are no open PRs addressing #13550 or the exact-subscription ancestor-notification gap. The change is limited to shouldSubscribeByName (single conditional) plus tests; no public API or exact semantics for sibling/descendant matching are altered.