Build all GC Roots into Cachix

[Dreamsorcerer]

No description provided.

[greptile-apps]

Greptile Summary

This PR updates the native-module CI path for Cachix-backed self-hosted runs. The main changes are:

• Builds native module outputs before self-hosted tests.
• Adds persistent Nix GC-root pinning for realized native outputs.
• Switches the self-hosted Nix setup to substitute-only mode.
• Limits the self-hosted Linux test container memory.
• Reduces native build worker parallelism.

Confidence Score: 5/5

This looks safe to merge from this follow-up pass.

• No new blocking issue was found in the latest changed code.
• The workflow changes are scoped to native build caching, substitution, and runner resource limits.

Important Files Changed

Filename	Overview
bin/build-cmu-nav-natives	Adds persistent GC-root pinning for native module outputs after build or warm-cache detection.
.github/workflows/ci.yml	Updates native build parallelism, self-hosted container memory limits, and substitute-only Nix configuration.

_{Reviews (2): Last reviewed commit: "Update ci.yml" | Re-trigger Greptile}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

❗ There is a different number of reports uploaded between BASE (66ce423) and HEAD (9dcc58a). Click for more details.

HEAD has 14 uploads less than BASE

Flag	BASE (66ce423)	HEAD (9dcc58a)
Py-3.14	2	0
OS-ubuntu-24.04-arm	1	0
Py-3.13	1	0
OS-ubuntu-latest	6	0
Py-3.11	1	0
Py-3.10	1	0
Py-3.14t	1	0
Py-3.12	1	0

@@             Coverage Diff             @@
##             main    #2866       +/-   ##
===========================================
- Coverage   72.21%   38.71%   -33.51%     
===========================================
  Files        1001      870      -131     
  Lines       89755    82665     -7090     
  Branches     8196     7552      -644     
===========================================
- Hits        64818    32005    -32813     
- Misses      22718    49503    +26785     
+ Partials     2219     1157     -1062     

Flag	Coverage Δ
OS-ubuntu-24.04-arm	?
OS-ubuntu-latest	?
Py-3.10	?
Py-3.11	?
Py-3.12	?
Py-3.13	?
Py-3.14	?
Py-3.14t	?
SelfHosted-Linux	37.40% <ø> (ø)
SelfHosted-macOS	35.81% <ø> (ø)

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see 646 files with indirect coverage changes

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[spomichter]

Assume this logic will be pulled out into generic format but will approve for now since i assume we need to merge to test if this change works

[Dreamsorcerer]

No, testing in the PR works fine.