feat: Allow nested registrations

[metal-messiah]

To facilitate inherent parent-child relationships with the planned register API, allow registered entities to expose their own .register() API for children of that entity to register with. Entities who register with the container agent will be related to the container. Entities that register under another registered entity will be related to both the container as well as the parent entity.

Overview

Related Issue(s)

NR-484626

Testing

new tests have been 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	26.18 kB / 9.86 kB (gzip)	26.18 kB / 9.86 kB (gzip)	0% / 0% (gzip)
lite	async-chunk	54.44 kB / 18.24 kB (gzip)	54.44 kB / 18.24 kB (gzip)	0% / 0% (gzip)
pro	loader	54.96 kB / 19.35 kB (gzip)	55.05 kB / 19.39 kB (gzip)	0.18% / 0.2% (gzip)
pro	async-chunk	93.17 kB / 29.2 kB (gzip)	93.17 kB / 29.2 kB (gzip)	0% / 0% (gzip)
spa	loader	63.81 kB / 22.05 kB (gzip)	63.91 kB / 22.09 kB (gzip)	0.15% / 0.2% (gzip)
spa	async-chunk	118.58 kB / 36.51 kB (gzip)	118.58 kB / 36.51 kB (gzip)	0% / 0% (gzip)

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.23%. Comparing base (aa8c02f) to head (74ca302).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/loaders/api/register.js	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1616      +/-   ##
==========================================
- Coverage   88.24%   88.23%   -0.01%     
==========================================
  Files         207      207              
  Lines        7800     7804       +4     
  Branches     1601     1605       +4     
==========================================
+ Hits         6883     6886       +3     
  Misses        800      800              
- Partials      117      118       +1     

Flag	Coverage Δ
unit-tests	81.54% <87.50%> (-0.01%)	⬇️

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[github-actions]

Last ran on November 12, 2025 12:12:05 CST
Checking merge of (86488f5) into main (c2785f3)