feat: clone story branch in ContainerRunner (ADR-007)

- Add BranchName field to task.Task (populated from story at execution time)
- Add GetStory to executor Store interface; resolve BranchName from story in both
  execute() and executeResume() parallel to RepositoryURL resolution
- Pass --branch <name> to git clone when BranchName is set; default clone otherwise

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/internal/executor/executor.go b/internal/executor/executor.go
index 440294c..6489060 100644
--- a/internal/executor/executor.go
+++ b/internal/executor/executor.go
@@ -33,6 +33,7 @@ type Store interface {
 	UpdateExecutionChangestats(execID string, stats *task.Changestats) error
 	RecordAgentEvent(e storage.AgentEvent) error
 	GetProject(id string) (*task.Project, error)
+	GetStory(id string) (*task.Story, error)
 }
 
 // LogPather is an optional interface runners can implement to provide the log
@@ -275,6 +276,12 @@ func (p *Pool) executeResume(ctx context.Context, t *task.Task, exec *storage.Ex
 			t.RepositoryURL = proj.RemoteURL
 		}
 	}
+	// Populate BranchName from Story if missing (ADR-007).
+	if t.BranchName == "" && t.StoryID != "" {
+		if story, err := p.store.GetStory(t.StoryID); err == nil && story.BranchName != "" {
+			t.BranchName = story.BranchName
+		}
+	}
 
 	err = runner.Run(ctx, t, exec)
 	exec.EndTime = time.Now().UTC()
@@ -715,6 +722,12 @@ func (p *Pool) execute(ctx context.Context, t *task.Task) {
 			t.RepositoryURL = proj.RemoteURL
 		}
 	}
+	// Populate BranchName from Story if missing (ADR-007).
+	if t.BranchName == "" && t.StoryID != "" {
+		if story, err := p.store.GetStory(t.StoryID); err == nil && story.BranchName != "" {
+			t.BranchName = story.BranchName
+		}
+	}
 
 	// Run the task.
 	err = runner.Run(ctx, t, exec)