fix(compile): detect and prevent workspace checkout collision with self repo

[jamesadevine]

Summary

When a workspace: entry references the same ADO repository that is already checked out as self, the compiled pipeline produces two checkout: steps that resolve to the same directory (s/<repo-name>). The second checkout overwrites the first, causing downstream steps (e.g. "Verify pipeline integrity") to fail because files from the self branch are replaced by the workspace branch.

Reproduction

1. Create an agent .md whose workspace: list includes the repo that also hosts the pipeline YAML (i.e. the self repo).
2. Compile with ado-aw compile.
3. Run the pipeline from a feature branch that has changes not yet on main.
4. The "Verify pipeline integrity" step fails:

Error: Failed to read pipeline file: component-governance.lock.yml Caused by: No such file or directory (os error 2)

Root Cause

In ADO multi-repo checkout, both checkout: self and checkout: repo-<self-repo-name> resolve to the same directory s/<repo-name>. The second checkout runs git clean -ffdx then checks out its configured ref (typically main), wiping files that only exist on the feature branch.

Observed in: Build 604639

• checkout: self → s/azure-devops-agentic-pipelines @ feature/failure-summary-agent ✅
• checkout: repo-azure-devops-agentic-pipelines → s/azure-devops-agentic-pipelines @ main — overwrites self ❌

Expected Behavior

The compiler should detect when a workspace:/checkout: entry references the same underlying repo as self and either:

1. Emit a compile-time error/warning explaining the collision, or
2. Automatically skip the redundant checkout (since self already provides access), or
3. Auto-assign a distinct path: to the workspace checkout to avoid the directory collision (e.g. s/repo-<alias> instead of s/<repo-name>)

Suggested Fix Location

src/compile/common.rs — validate_checkout_list() or the checkout generation logic. The compiler already has access to the self repo identity and the workspace repo list at compile time, so a comparison is straightforward.

Environment

• ado-aw version: v0.26.0
• Pipeline: OS+Tooling CG Purview (component-governance.lock.yml)
• Agent pool: AZS-1ES-L-MMS-ubuntu-22.04
• OS: Ubuntu 22.04