Creating backend abstraction for self hosted worker (#29)

Co-authored-by: Oz <oz-agent@warp.dev>

Author: ianhodge

internal/worker/backend.go

@@ -0,0 +1,43 @@
+package worker
+
+import (
+	"context"
+
+	"github.com/warpdotdev/oz-agent-worker/internal/types"
+)
+
+// TaskParams contains pre-processed task parameters common to all backends.
+// This provides a layer of abstraction between the wire-format TaskAssignmentMessage
+// and the backend interface, so backends don't need to handle common concerns like
+// resolving environment variables, choosing default images, or building base CLI args.
+type TaskParams struct {
+	TaskID string
+	Task   *types.Task
+
+	// EnvVars contains pre-resolved common environment variables (TASK_ID, Git config,
+	// assignment env vars). Backends append their own config-specific env vars.
+	EnvVars []string
+
+	// BaseArgs contains the base CLI arguments for the agent command
+	// (agent run --share ... --task-id ... --server-root-url ... + augmented args).
+	// Backends prepend their invocation prefix and append backend-specific flags.
+	BaseArgs []string
+
+	// DockerImage is the resolved Docker image name (with default fallback applied).
+	// Backends that don't use Docker can ignore this.
+	DockerImage string
+
+	// Sidecars is the unified list of sidecar mounts for this task. The Warp agent
+	// sidecar (mounted at /agent) is included as the first entry when present, followed
+	// by any additional sidecars from the assignment. Backends that don't use sidecars
+	// can ignore this.
+	Sidecars []types.SidecarMount
+}
+
+// Backend defines the interface for task execution backends.
+type Backend interface {
+	// ExecuteTask runs the agent for the given task parameters.
+	ExecuteTask(ctx context.Context, params *TaskParams) error
+	// Shutdown cleans up backend resources.
+	Shutdown(ctx context.Context)
+}