Update error message in GitOps when unknown env vars are encountered

[sgress454]

Related issue: Resolves #44053

Checklist for submitter

If some of the following don't apply, delete the relevant line.

• Changes file added for user-visible changes in changes/, orbit/changes/ or ee/fleetd-chrome/changes.
  See Changes files for more information.

Testing

• Added/updated automated tests
• QA'd all new/changed functionality manually

Summary by CodeRabbit

• Bug Fixes
  • Error messages for undefined environment variables in GitOps configurations now include clearer, actionable guidance with examples of how to escape literal dollar-sign syntax (e.g., showing escaped forms). This improves clarity when a variable is missing and helps users distinguish between intended variable references and literal values, reducing confusion.

[claude]

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[Copilot]

Pull request overview

This PR improves the GitOps environment-variable error message so users who intended literal $VAR text are told how to escape it, addressing the round-trip issue described in #44053.

Changes:

• Adds escape guidance to missing environment variable errors in expandEnv.
• Updates unit and GitOps tests to expect the new message.
• Adds a changelog entry for the user-visible error message improvement.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
pkg/spec/spec.go	Builds a clearer missing-env-var error with $VAR / ${VAR} escape guidance.
pkg/spec/spec_test.go	Updates TestExpandEnv expectations for the new error wording.
pkg/spec/gitops_test.go	Updates GitOps missing-env-var assertion for the new message.
changes/44053-improve-env-var-error-msg	Documents the user-visible GitOps error message update.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 3dbedb77-73ab-4422-a1ef-28ffd0b605d7

📥 Commits

Reviewing files that changed from the base of the PR and between 418e221 and 08f3330.

📒 Files selected for processing (1)

• changes/44053-improve-env-var-error-msg

✅ Files skipped from review due to trivial changes (1)

• changes/44053-improve-env-var-error-msg

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Walkthrough

This PR improves error messages shown when GitOps files reference undefined environment variables. expandEnv now reports which variable is unset and shows how to escape the literal form used in the source (e.g., advise \$VAR for $VAR or \${VAR} for ${VAR}). Tests were updated to verify the exact new messages and a changelog entry documents the change.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: updating the error message for unknown environment variables in GitOps.
Description check	✅ Passed	The description includes the related issue (#44053), indicates a changes file was added, automated tests were updated, and manual QA was performed.
Linked Issues check	✅ Passed	The code changes directly address issue #44053 by improving error messages to advise users how to escape literal dollar signs in environment variable references.
Out of Scope Changes check	✅ Passed	All changes are scoped to the linked issue: a changes file, error message improvements in spec.go, and corresponding test updates in spec_test.go and gitops_test.go.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch sgress454/44053-escape-in-generate-gitops

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.81%. Comparing base (1f934e1) to head (08f3330).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #46476      +/-   ##
==========================================
- Coverage   66.81%   66.81%   -0.01%     
==========================================
  Files        2809     2809              
  Lines      223584   223588       +4     
  Branches    11309    11309              
==========================================
- Hits       149382   149381       -1     
- Misses      60647    60649       +2     
- Partials    13555    13558       +3     

Flag	Coverage Δ
backend	68.53% <100.00%> (-0.01%)	⬇️

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