Propagate P4CLIENT and BUILD_REF to agent subprocess environment

- Add P4Client field to CheckoutResult so the worker can pass the
  workspace name to graph execution
- Set P4CLIENT and BUILD_REF in the subprocess env
- Add CredentialTypeP4 to core credential types

Author: sebastianrath

agent/vcs/p4.go

@@ -93,7 +93,7 @@ func (p *P4Provider) Checkout(ctx context.Context, url, ref, pipeline, destDir s
 			return CheckoutResult{}, fmt.Errorf("p4 sync pipeline file failed: %w", err)
 		}
 
-		return CheckoutResult{Dir: root, Persistent: true}, nil
+		return CheckoutResult{Dir: root, Persistent: true, P4Client: p.clientName}, nil
 	}
 
 	// Create temporary workspace
@@ -132,7 +132,7 @@ func (p *P4Provider) Checkout(ctx context.Context, url, ref, pipeline, destDir s
 		return CheckoutResult{}, fmt.Errorf("p4 sync pipeline file failed: %w", err)
 	}
 
-	return CheckoutResult{Dir: absDir}, nil
+	return CheckoutResult{Dir: absDir, P4Client: p.clientName}, nil
 }
 
 func (p *P4Provider) Cleanup(ctx context.Context) error {

agent/vcs/vcs.go

@@ -33,6 +33,10 @@ type CheckoutResult struct {
 	Persistent bool
 	// SHA is the resolved commit SHA (or changelist number for P4) after checkout.
 	SHA string
+	// P4Client is the Perforce workspace name created or reused during checkout.
+	// The worker should set P4CLIENT in the subprocess environment so that
+	// p4 commands within the graph can operate on the same workspace.
+	P4Client string
 }
 
 // Provider handles VCS checkout operations.

agent/worker.go

@@ -358,12 +358,16 @@ func (w *Worker) execute(ctx context.Context, job *ClaimResponse) {
 	env = append(env, "BUILD_TMPDIR="+tmpDir)
 	env = append(env, "BUILD_VCS_TYPE="+job.VCSType)
 	env = append(env, "BUILD_VCS_URL="+job.VCSURL)
+	env = append(env, "BUILD_REF="+ref)
 	if job.RepoID != "" {
 		env = append(env, "BUILD_REPO_ID="+job.RepoID)
 	}
 	if checkout.SHA != "" {
 		env = append(env, "BUILD_COMMIT_SHA="+checkout.SHA)
 	}
+	if checkout.P4Client != "" {
+		env = append(env, "P4CLIENT="+checkout.P4Client)
+	}
 
 	// Resolve env mappings from trigger config (if present)
 	if len(job.EnvMappings) > 0 && job.MatrixValues != nil {

core/base.go

@@ -49,6 +49,7 @@ const (
 	CredentialTypeSSH CredentialType = iota
 	CredentialTypeUsernamePassword
 	CredentialTypeAccessKey
+	CredentialTypeP4
 )
 
 type Credentials interface {