feat: add self-repository action reference syntax

[nodeselector]

$/ — self-referencing action syntax

Adds $/path as a new uses: syntax meaning "this repo, at this SHA, at the given subpath." The containing YAML file determines which repo and SHA — so $/lib/helper inside acme/toolkit@v1 resolves to acme/toolkit at that SHA with path lib/helper, not the caller's repo.

Why

Composite actions that ship multiple sub-actions in one repo currently hardcode owner/repo@ref to reference siblings. This creates a circular versioning problem — you can't cut a release tag until the YAML already references that tag. $/ breaks the cycle: siblings reference each other by path, and the ref is inherited from whatever version the caller pinned.

Feature flag

actions_dollar_self_reference — gates parsing (Launch → parser), server-side resolution (ARS), and runner-side resolution. Unified name across all four repos.

How it works

Parsing. Both template converters (PipelineTemplateConverter for action.yml, WorkflowTemplateConverter for workflow YAML) detect $/ via PipelineConstants.TryParseDollarSelfReference(). The parsed reference gets RepositoryType = "selfRepository" and Path = <subpath> — no Name or Ref yet. Leading slashes are stripped and bare $/ (no subpath) is rejected.

Resolution. ActionManager.ResolveDollarSelfReferences() rewrites selfRepository refs to concrete GitHub-type refs in-place before they reach any download logic:

Depth	Source of truth	Why
0 (workflow steps)	job.WorkflowRepository / job.WorkflowSha	Points to the repo containing the workflow file. Correct for both regular and reusable workflows.
> 0 (inside composites)	Parent action's RepositoryPathReference.Name / .Ref	The parent is already resolved. $/ in a child always means "the repo that contains me."

After resolution, the ref is indistinguishable from a normal owner/repo/path@sha reference.

Both resolution paths supported. Works on both the batch resolution path (PrepareActionsRecursiveAsync, gated on actions_batch_action_resolution) and the legacy serial path (PrepareActionsRecursiveLegacyAsync). The batch path is not yet broadly rolled out, so legacy support is required.

Upfront resolution (not lazy). All $/ refs are resolved during PrepareActionsAsync (Setup Job phase) before any step executes. Pre/post step registration depends on the complete recursive walk having finished, so lazy resolution would break it.

Runtime re-resolution. LoadAction re-parses action.yml from disk at execution time, producing fresh RepositoryPathReference objects with RepositoryType = "selfRepository". ResolveDollarSelfReferences runs again using the parent's already-resolved Name/Ref. No network calls — the tarball is already cached.

Safety net. GetDownloadInfoLookupKey throws InvalidOperationException if a selfRepository ref reaches it unresolved.

Cross-repo $/ context propagation

private-server-1/actions/crossrepo-chain/action.yml
  └─ uses: github/public-server/actions/leaf@sha
       └─ leaf/action.yml says: uses: $/actions/other-leaf
          → resolves to public-server/actions/other-leaf@sha  ✅
          (NOT private-server-1 — $/ means the repo containing THIS file)

This works because childRepoName/childRepoRef at each depth come from the parent action's resolved RepositoryPathReference.Name/.Ref, not from the workflow-level context.

Tests (7 total)

• ResolvesAtDepthZero — batch path, top-level $/ resolution
• ResolvesAtDepthZero_LegacyPath — legacy path equivalent
• NotResolvedWhenFeatureFlagDisabled — $/ stays unresolved, hits safety net
• ResolvesNestedInComposite — depth-1 $/ inside a composite (batch)
• ResolvesNestedInComposite_LegacyPath — legacy path equivalent
• CrossRepoCompositeResolvesToParentRepo — $/ resolves to parent's repo, not caller's
• MultiLevelChain — 3-level composite chain with $/ at each depth

[Copilot]

Pull request overview

This PR introduces a new uses: syntax $/path (“dollar-self”) to allow actions and workflows to reference sub-actions within the same repository at the pinned SHA, eliminating circular versioning for composite actions.

Changes:

• Added parsing support for $/ in both the workflow parser (WorkflowTemplateConverter) and pipeline template converter (PipelineTemplateConverter) via a shared PipelineConstants.TryParseDollarSelfReference() helper.
• Implemented upfront and runtime resolution of dollar-self references in ActionManager so they are rewritten into concrete owner/repo/path@sha GitHub refs before download/prepare/load logic.
• Added L0 tests covering depth-0 resolution, nested composites, cross-repo context propagation, multi-level chains, and legacy (non-batch) resolution.

Show a summary per file

File	Description
src/Test/L0/Worker/ActionManagerL0.cs	Adds L0 coverage for dollar-self resolution across batch + legacy code paths.
src/Sdk/WorkflowParser/WorkflowConstants.cs	Defines DollarSelfAlias for workflow parsing/id generation.
src/Sdk/WorkflowParser/Conversion/WorkflowTemplateConverter.cs	Detects $/ uses values when generating default step IDs.
src/Sdk/DTPipelines/Pipelines/PipelineConstants.cs	Introduces DollarSelfAlias, DollarSelfPrefix, and TryParseDollarSelfReference().
src/Sdk/DTPipelines/Pipelines/ObjectTemplating/PipelineTemplateConverter.cs	Parses $/path into RepositoryPathReference with RepositoryType = dollar-self.
src/Runner.Worker/ActionManager.cs	Resolves dollar-self refs before batching/downloading and again at load-time for re-parsed composites; adds safety-net throw if unresolved reaches lookup.
src/Runner.Common/Constants.cs	Adds actions_dollar_self_reference feature flag constant.

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 9
• Review effort level: Low