Add agent and skill system: implement Agent and Skill classes, register media and naked agents, and create media_info demo skill

skills/__init__.py

@@ -0,0 +1,50 @@
+"""
+Skill system — each skill is a piece of domain knowledge or a capability
+that can be attached to an agent to shape its behavior and system prompt.
+
+A Skill is a lightweight object with:
+- name        : short identifier (e.g. "media_info")
+- description : human-readable summary
+- prompt_fragment : extra text injected into the agent's system prompt
+"""
+
+from dataclasses import dataclass, field
+from typing import Dict
+
+
+@dataclass
+class Skill:
+    name: str
+    description: str
+    prompt_fragment: str = ""
+
+
+# ---------------------------------------------------------------------------
+# Global skill registry — populated at startup / import time
+# ---------------------------------------------------------------------------
+_skill_registry: Dict[str, Skill] = {}
+
+
+def register(skill: Skill) -> None:
+    """Register a skill so agents can look it up by name."""
+    _skill_registry[skill.name] = skill
+
+
+def get(name: str) -> Skill | None:
+    """Return a registered skill by name, or None."""
+    return _skill_registry.get(name)
+
+
+def list_all() -> Dict[str, Skill]:
+    """Return a shallow copy of the registry."""
+    return dict(_skill_registry)
+
+
+def get_combined_prompt(skill_names: list[str], base_prompt: str = "") -> str:
+    """Build a system prompt from a base prompt + requested skill fragments."""
+    parts = [base_prompt] if base_prompt else []
+    for name in skill_names:
+        s = get(name)
+        if s and s.prompt_fragment:
+            parts.append(s.prompt_fragment)
+    return "\n\n".join(parts)