🤖 Fix fleetd escrow in X11 multi-user sessions

[lucasmrod]

Related issue: Resolves #31633.

Main change is stop relying on who command output to get the value of the DISPLAY variable on X11 sessions (old distributions), and instead search the value of the DISPLAY variable in processes that are owned by the target user.

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

Testing

• QA'd all new/changed functionality manually

fleetd/orbit/Fleet Desktop

• Verified compatibility with the latest released version of Fleet (see Must rule)
• If the change applies to only one platform, confirmed that runtime.GOOS is used as needed to isolate changes
• Verified that fleetd runs on macOS, Linux and Windows
• Verified auto-update works from the released version of component to the new version (see tools/tuf/test)

Summary by CodeRabbit

• Bug Fixes
  • Enhanced X11 session detection for improved support in multi-session environments, providing more reliable display variable identification in complex session configurations.

[lucasmrod]

@coderabbitai review

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Walkthrough

The pull request modifies the X11 display detection mechanism in the Linux user execution module. It refactors the getDisplayVariableForSession function by removing the user parameter and changing the implementation from using the system who command to a procfs-based approach. The new implementation reads DISPLAY environment variables directly from /proc filesystem entries. Helper functions are introduced to read environment variables from /proc files. Legacy code that parsed who command output is removed. Tests are updated to validate the new procfs-based environment reading functionality, including error handling for missing environ files.

🚥 Pre-merge checks | ✅ 4 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 44.44% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Description check	⚠️ Warning	The PR description is largely incomplete compared to the template requirements. Most testing and verification checkboxes are either unchecked or missing details.	Add details for: automated tests (added/updated), SQL validation if applicable, load testing confirmation for bug fixes, and complete all remaining verification checkboxes for fleetd/orbit/Fleet Desktop changes.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Fix fleetd escrow in X11 multi-user sessions' clearly summarizes the main change, addressing the primary objective of fixing the disk encryption popup issue in multi-user X11 environments.
Linked Issues check	✅ Passed	The code changes directly address the linked issue #31633 by improving DISPLAY variable detection in X11 multi-user sessions through procfs-based discovery instead of external 'who' command execution.
Out of Scope Changes check	✅ Passed	All changes are focused on improving X11 display detection for multi-user sessions. The refactoring of display retrieval logic, transition from 'who' command to procfs-based approach, and corresponding test updates are all directly aligned with fixing the disk encryption popup issue.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into 34501-fix-fleet-desktop-gui-sessions

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch 34501-fix-fleetd-escrow-multi-sessions-x11

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[codecov]

Codecov Report

❌ Patch coverage is 23.68421% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.27%. Comparing base (0823cc7) to head (81c7512).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
orbit/pkg/execuser/execuser_linux.go	23.68%	29 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #39795   +/-   ##
=======================================
  Coverage   66.27%   66.27%           
=======================================
  Files        2439     2439           
  Lines      195442   195409   -33     
  Branches     8551     8591   +40     
=======================================
- Hits       129528   129510   -18     
+ Misses      54179    54170    -9     
+ Partials    11735    11729    -6     

Flag	Coverage Δ
backend	68.07% <23.68%> (-0.01%)	⬇️

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The base branch was changed.