feat: add support for mfe tags with the register API

[metal-messiah]

Adds support for adding entity tags through the usage of the register API

Overview

Related Issue(s)

https://new-relic.atlassian.net/browse/NR-504993?atlOrigin=eyJpIjoiZTQ0MGJjY2RjZGIzNGIyNjg5YTdmOTljNWI4OTc1OWEiLCJwIjoiaiJ9

Testing

Tests have been added to ensure that protected keys remain protected and expected attributes are present when tags are added

[github-actions]

Supportability Metric Usage Changes:

No matching changes found

Supportability Metrics .md File Changes:

supportability_metrics.md was changed? false

New supportability metrics require changes to supportability_metrics.md, as well as a new PR to Angler. Please ensure an Angler PR is created and linked to this PR.

[github-actions]

Asset Size Report

Merging this pull request will result in the following asset size changes:

Agent	Asset	Previous Size	New Size	Diff
lite	loader	27.18 kB / 10.25 kB (gzip)	27.18 kB / 10.25 kB (gzip)	0% / 0% (gzip)
lite	async-chunk	54.67 kB / 18.32 kB (gzip)	54.67 kB / 18.32 kB (gzip)	0% / 0% (gzip)
pro	loader	59.75 kB / 20.78 kB (gzip)	59.85 kB / 20.82 kB (gzip)	0.18% / 0.22% (gzip)
pro	async-chunk	93.54 kB / 29.57 kB (gzip)	93.54 kB / 29.57 kB (gzip)	0% / 0% (gzip)
spa	loader	68.71 kB / 23.58 kB (gzip)	68.82 kB / 23.62 kB (gzip)	0.15% / 0.17% (gzip)
spa	async-chunk	118.98 kB / 36.69 kB (gzip)	118.98 kB / 36.69 kB (gzip)	0% / 0% (gzip)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.35%. Comparing base (a429d42) to head (479c2d8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1660   +/-   ##
=======================================
  Coverage   88.35%   88.35%           
=======================================
  Files         207      207           
  Lines        7910     7912    +2     
  Branches     1641     1643    +2     
=======================================
+ Hits         6989     6991    +2     
  Misses        804      804           
  Partials      117      117           

Flag	Coverage Δ
unit-tests	81.94% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[github-actions]

Last ran on December 30, 2025 11:34:50 CST
Checking merge of (211659f) into main (c284cfd)