process: return unregister fn from finalization

[mcollina]

process.finalization.register() and process.finalization.registerBeforeExit() now return a function that removes that specific registration:

const unregister = process.finalization.register(obj, onExit);
// later
unregister();

Other registrations for the same object are left in place, calling the function more than once is a no-op, and the function does not hold a strong reference to obj.

Each registration now uses its WeakRef as the FinalizationRegistry unregister token. This also fixes process.finalization.unregister(obj), which called registry.unregister(obj) although obj was never passed as a token, so the registry entries were never removed.

---

AI generated. Reviewed by me.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.43%. Comparing base (8bf7793) to head (e214630).
⚠️ Report is 188 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66482      +/-   ##
==========================================
+ Coverage   90.39%   90.43%   +0.03%     
==========================================
  Files         792      790       -2     
  Lines      275580   275448     -132     
  Branches    52840    52833       -7     
==========================================
- Hits       249104   249091      -13     
+ Misses      16897    16765     -132     
- Partials     9579     9592      +13     

Files with missing lines	Coverage Δ
lib/internal/process/finalization.js	100.00% <100.00%> (ø)

... and 69 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78197/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78271/

[nodejs-github-bot]

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----------------------------------- PR info ------------------------------------
Title      process: return unregister fn from finalization (#66482)
Author     Matteo Collina <matteo.collina@gmail.com> (@mcollina)
Branch     mcollina:process-finalization-unregister-fn -> nodejs:main
Labels     process, needs-ci, commit-queue, lacks-second-approval
Commits    1
 - process: return unregister fn from finalization
Committers 1
 - Matteo Collina <hello@matteocollina.com>
PR-URL: https://github.com/nodejs/node/pull/66482
Reviewed-By: James M Snell <jasnell@gmail.com>
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/66482
Reviewed-By: James M Snell <jasnell@gmail.com>
--------------------------------------------------------------------------------
   ℹ  This PR was created on Sat, 03 Oct 2026 14:33:02 GMT
   ✔  Approvals: 1
   ✔  - James M Snell (@jasnell) (TSC): https://github.com/nodejs/node/pull/66482#pullrequestreview-5420245948
   ✖  This PR needs to wait 5 more hours to land (or 0 minutes if there is one more approval)
   ⚠  This PR has conflicts that must be resolved
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