fix(ci): use explicit SHA for paths-filter ref in desktop E2E

[FSM1]

Summary

• ref: HEAD fails in paths-filter because it does git show-ref HEAD which finds no match in detached HEAD state
• Use github.event.workflow_run.head_sha (the actual commit SHA) for both base parent resolution and ref

Test plan

• Merge and verify the desktop E2E Detect Changes job passes

🤖 Generated with Claude Code

Summary by CodeRabbit

Release Notes

No user-facing changes. This release includes an internal infrastructure update to the CI/CD workflow configuration that optimizes test execution paths. End-users will not be affected by these changes.

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 9115263 and 0b47133.

📒 Files selected for processing (1)

• .github/workflows/e2e-desktop.yml

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Walkthrough

A single line in the e2e-desktop GitHub Actions workflow was modified to change the ref value used by the paths-filter step from HEAD to ${{ github.event.workflow_run.head_sha }}. This alters which commit serves as the reference for filtering changed files without affecting other workflow logic.

Changes

Cohort / File(s)	Summary
GitHub Actions Workflow Configuration .github/workflows/e2e-desktop.yml	Modified the ref parameter in the paths-filter step to use the workflow run's head SHA instead of HEAD, changing the base commit reference for path filtering.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• fix(ci): consolidate desktop E2E pipeline and add Rust tests #227 — Introduces or modifies the paths-filter step behavior in e2e-desktop workflow that this PR directly alters.
• ci: skip expensive jobs on docs/planning-only PRs #195 — Modifies dorny/paths-filter usage in GitHub Actions workflows, related to the same path-filter refactoring pattern.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: using an explicit SHA for the paths-filter ref in the desktop E2E workflow to fix a detached HEAD issue.
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
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/desktop-e2e-paths-filter-ref

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