Introduce "agents"

An agent is currently a name given to a system prompt and a set of
tools which the agent has access to.

This resolves the previous issue of the set of configured tools being
available in *all* contexts, which wasn't always desired. Tools are now
only available when an agent is explicitly requested using the
`-a/--agent` flag.

Agents are expected to be expanded on: the concept of task-specilized
agents (e.g. coding), the ability to define a set of files an agent
should always have access to for RAG purposes, etc.

Other changes:

- Removes the "tools" top-level config structure (though this is expected
to come back along with the abillity to define custom tools).

- Renamed `pkg/agent` to `pkg/agents`

pkg/agents/toolbox/util/util.go

@@ -0,0 +1,67 @@
+package util
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// isPathContained attempts to verify whether `path` is the same as or
+// contained within `directory`. It is overly cautious, returning false even if
+// `path` IS contained within `directory`, but the two paths use different
+// casing, and we happen to be on a case-insensitive filesystem.
+// This is ultimately to attempt to stop an LLM from going outside of where I
+// tell it to. Additional layers of security should be considered.. run in a
+// VM/container.
+func IsPathContained(directory string, path string) (bool, error) {
+	// Clean and resolve symlinks for both paths
+	path, err := filepath.Abs(path)
+	if err != nil {
+		return false, err
+	}
+
+	// check if path exists
+	_, err = os.Stat(path)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return false, fmt.Errorf("Could not stat path: %v", err)
+		}
+	} else {
+		path, err = filepath.EvalSymlinks(path)
+		if err != nil {
+			return false, err
+		}
+	}
+
+	directory, err = filepath.Abs(directory)
+	if err != nil {
+		return false, err
+	}
+	directory, err = filepath.EvalSymlinks(directory)
+	if err != nil {
+		return false, err
+	}
+
+	// Case insensitive checks
+	if !strings.EqualFold(path, directory) &&
+		!strings.HasPrefix(strings.ToLower(path), strings.ToLower(directory)+string(os.PathSeparator)) {
+		return false, nil
+	}
+
+	return true, nil
+}
+
+func IsPathWithinCWD(path string) (bool, string) {
+	cwd, err := os.Getwd()
+	if err != nil {
+		return false, "Failed to determine current working directory"
+	}
+	if ok, err := IsPathContained(cwd, path); !ok {
+		if err != nil {
+			return false, fmt.Sprintf("Could not determine whether path '%s' is within the current working directory: %s", path, err.Error())
+		}
+		return false, fmt.Sprintf("Path '%s' is not within the current working directory", path)
+	}
+	return true, ""
+}