[Changelog] Reference same-repository actions with self-repository syntax

[plengauer]

GitHub has introduced a new `(redacted) syntax for referencing actions within the same repository, announced in the July 30, 2026 changelog post.

What changed

GitHub Actions now supports a (redacted) (or similar self-repository) syntax that allows workflows to reference actions in the same repository without using the ./` relative path prefix. This is a cleaner, more explicit way to reference same-repo actions.

Relevance to this project

This project heavily uses relative path references to its own actions throughout its CI/CD workflows:

• ./actions/instrument/job — used in test_github.yml, experiment.yml, and others
• Reusable workflows referenced as ./.github/workflows/build.yml, ./.github/workflows/test_shell.yml, etc.

Additionally, the documentation and instrumentation examples encourage users to reference this project's actions (e.g., plengauer/Thoth/actions/instrument/job@main), but for in-repo usage the new syntax may provide benefits.

What needs investigation / action

1. Review the new syntax: Understand what `(redacted) syntax looks like and whether it offers advantages (cleaner, works in more contexts, avoids path resolution issues).
2. Consider adopting the new syntax in the project's own workflow files to replace ./actions/instrument/job references, if it improves clarity or compatibility.
3. Update documentation: If the new syntax is relevant for users instrumenting their own workflows from the same repo, update any examples or guides.
4. Check for edge cases: The ./ relative path syntax may behave differently in reusable workflows or composite actions — the new syntax may resolve some known pain points.

Affected areas

• .github/workflows/test_github.yml — multiple uses: ./actions/instrument/job references
• .github/workflows/experiment.yml
• All workflow documentation/examples

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[github-actions]

Triage Analysis

This issue tracks adoption of the new GitHub Actions self-repository syntax for referencing same-repo actions, announced in the [July 30, 2026 changelog]((github.blog/redacted)

Scope is clear:

• Replace ./actions/instrument/job style references with the new syntax in workflow files
• Affected files are already identified: .github/workflows/test_github.yml, .github/workflows/experiment.yml, and other workflows using reusable workflow references like ./.github/workflows/build.yml

Suggested approach:

1. Fetch and read the changelog post to understand the exact new syntax
2. Audit all .github/workflows/*.yml files for ./actions/ and ./.github/workflows/ references
3. Replace applicable references with the new self-repository syntax
4. Update any documentation or example files that show in-repo action references

This looks straightforward enough to assign to Copilot.

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