fix: set zarf version in the user-agent field of oci-client

[samayer12]

Summary

Fix Zarf OCI remote setup so registry requests include the expected User-Agent: zarf/<CLI version> header.

zoci.NewRemote() previously passed the user-agent as a modifier into oci.NewOrasRemote(), but the underlying OCI wrapper replaces the ORAS auth client during repository setup. That replacement dropped the configured header, so UDS Registry observed Go's default Go-http-client/2.0 instead of the Zarf version.

This change applies the Zarf user-agent after oci.NewOrasRemote() returns, ensuring it is set on the final client used for publish, pull, copy, and related OCI operations.

See https://github.com/defenseunicorns/uds-registry/pull/3206 for the original PR that discovered this bug.

Fixes #5226

Changes

• Apply oci.WithUserAgent("zarf/" + config.CLIVersion) after oci.NewOrasRemote() returns in zoci.NewRemote().
• Add a regression test that verifies the final ORAS auth client has User-Agent: zarf/<CLI version>.

Validation

go test ./src/pkg/zoci -run TestNewRemoteSetsZarfUserAgentOnFinalClient -count=1
go test ./src/pkg/zoci -count=1

Post-fix Evidence

Successful post-fix metric showing the client family and version were detected by UDS Registry metrics:

{
  "metric": {
    "client_family": "zarf",
    "client_version": "0.82.x",
    "result": "accepted"
  },
  "value": [
    1786721539.717,
    "1"
  ]
}

[netlify]

✅ Deploy Preview for zarf-docs canceled.

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[brandtkeller]

Hmm.. Something looks funky on the netlify actions. @samayer12 could you merge the latest changes from main into this branch?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
src/pkg/zoci/common.go	75.00% <100.00%> (ø)

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[samayer12]

@brandtkeller updated from main, looks like that solved the netlify issue

[AustinAbro321]

@samayer12 Thanks for the find! It seems this is a bug in defenseunicorns/pkg/oci. Could you instead add this fix there? I wouldn't be surprised if this bug was also affecting uds-cli.

[samayer12]

@AustinAbro321 sure thing, I'll close this PR and open one over there instead

[AustinAbro321]

@samayer12 Wait! I think our friend @Racer159 is already fixing this in defenseunicorns/pkg#202, which I'm reviewing now. Awesome timing hahaha

[brandtkeller]

@samayer12 please review defenseunicorns/pkg#202 first as I believe it fixes this issue?

[AustinAbro321]

Another timing coincidence @brandtkeller !!

[samayer12]

Yep, this looks great. Specifically, this test case on the user-agent covers what we're after.