🧹 chore: remove dead code and stale api-extractor report

[saulo-silva]

Proposed Changes

This PR removes two dead internal modules and a stale API report file, and aligns the api-extractor config with the report it actually generates.

Dead code (only referenced by their own test files):

• src/utils/deepMerge.ts — orphaned since 9d22c8b (fix issue: Populating form with reset and keepDefaultValues as true breaks fieldarray actions #7109, Nov 2021) removed its last production call site. No imports anywhere in src/ outside its own test since then.
• src/logic/getNodeParentName.ts — orphaned after f29f546 (👯 combine duplicated code #13328) consolidated its call sites; the logic it used to serve now lives in isNameInFieldArray, which handles nested field arrays correctly. Also updated a comment in isNameInFieldArray.test.ts that referenced the removed function.

Both modules are already tree-shaken from the published bundle, so there is no runtime or bundle-size impact — this is purely source hygiene (−107 lines of unused code and tests).

Stale API report:

• Deleted reports/api-extractor.md — api-extractor enforces the .api.md extension, so the report is actually generated and validated as reports/api-extractor.md.api.md. The old file stopped being rewritten (last touched Mar 2025) and has drifted ~500 lines behind: it is missing Watch, FormStateSubscribe, setValues, the current Controller signature, and more, while still being tracked in git as if it were the public API report.
• Set reportFileName to api-extractor.api.md in api-extractor.json (matching the extension requirement documented in the config itself) and renamed the generated report accordingly: reports/api-extractor.md.api.md → reports/api-extractor.api.md. Re-running pnpm api-extractor:build reproduces the renamed file with no diff, and pnpm api-extractor:ci passes.

Type of change

• None of the listed options — internal cleanup with no runtime, public API, or bundle changes

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• New and existing tests pass locally with my changes (pnpm test: 118 suites / 1215 tests, pnpm test:type, pnpm lint, pnpm build, pnpm api-extractor:ci)

[saulo-silva]

Heads-up on the failing playwright-run check: the useFieldArrayUnregister.spec.ts failure appears to be a pre-existing flake on master, unrelated to this PR (which only removes files with no production importers — dist/index.esm.mjs builds byte-identical to master's).

Evidence from local runs of pnpm e2e useFieldArrayUnregister --repeat-each=3:

• this branch: 3/3 failed
• master (9fde5f3): one invocation passed 3/3, two subsequent invocations failed — same assertion as CI (the dirtyFields poll after move(4, 2), missing conditional: true at index 2)

The Playwright page snapshot at the failure point shows the conditional input at index 2 is mounted and touchedFields moved { name, conditional } to index 2 correctly — but dirtyFields lost the conditional flag. So it looks like a timing race between the move() dirty-state recomputation and the conditional field's unregister({ keepDirty: true }) / re-register effect cycle, rather than anything in this diff.

I've re-pushed to retrigger CI. Happy to open a separate issue with the full repro details if that's useful.

[bluebill1049]

LGTM 🙏