T14 — Markdown-based skill system + frontmatter discovery

{`
def load_all_skills(plugin_dirs: list[Path] | None = None) -> list[Skill]:
    skills: list[Skill] = []
    seen_names: set[str] = set()

    # 1. Bundled skills (ship cùng với package)
    bundled = Path(__file__).parent / "bundled"
    skills.extend(_load_from_dir(bundled, seen_names))

    # 2. User skills (~/.openharness/skills/<skill>/SKILL.md)
    user_dir = Path.home() / ".openharness" / "skills"
    if user_dir.exists():
        skills.extend(_load_from_dir(user_dir, seen_names))

    # 3. Plugin-contributed skills (từ plugin manifest)
    for plugin_dir in (plugin_dirs or []):
        skills_path = plugin_dir / "skills"
        if skills_path.exists():
            skills.extend(_load_from_dir(skills_path, seen_names))

    return skills
`}

{`
def _parse_skill_file(path: Path) -> Skill | None:
    text = path.read_text(encoding="utf-8")

    # Try YAML frontmatter (--- ... ---)
    if text.startswith("---"):
        end = text.index("---", 3)
        fm = yaml.safe_load(text[3:end])
        body = text[end + 3:].strip()
        return Skill(
            name=fm.get("name") or path.parent.name,
            description=fm.get("description", ""),
            body=body,
            source=path,
        )

    # Fallback: heading + first paragraph
    lines = text.splitlines()
    name = lines[0].lstrip("# ").strip() if lines else path.parent.name
    desc = next((l for l in lines[1:] if l.strip()), "")
    return Skill(name=name, description=desc, body=text, source=path)
`}

{`
def _build_skills_section(skills: list[Skill], permitted: set[str]) -> str:
    visible = [s for s in skills if s.name in permitted]
    if not visible:
        return ""
    lines = ["## Available Skills", ""]
    for s in visible:
        lines.append(f"- **{s.name}**: {s.description}")
    lines.append("")
    lines.append("Invoke a skill with /skill-name or ask me to use it by name.")
    return "\n".join(lines)
`}

{`
# Directory: ~/.openharness/skills/code-review/SKILL.md
---
name: code_review   # BUG: dùng underscore, directory dùng hyphen
description: Review code changes
---

# Kết quả: skill không được load vào seen_names
# Agent không biết skill tồn tại → user invoke /code_review → "skill not found"

# Fix: name phải khớp với directory name
---
name: code-review
description: Review code changes
---
`}

{`
# BAD: SKILL.md body 2000 dòng với inline templates, examples, code snippets
# → Mỗi lần invoke: load 2000 dòng vào context
# → Tốn ~4000+ tokens chỉ cho skill body
# → Ít chỗ cho tool results và conversation

# GOOD: Progressive disclosure
# SKILL.md body: < 200 dòng (what + how summary)
# skills/code-review/
#   SKILL.md       ← summary + references
#   checklist.md   ← detailed checklist (load on-demand)
#   template.py    ← code template (load on-demand)
`}

{`
from dataclasses import dataclass
from pathlib import Path
import yaml

@dataclass
class Skill:
    name: str
    description: str
    body: str  # không inject vào system prompt mặc định
    source: Path

def load_skills(dirs: list[Path]) -> list[Skill]:
    skills, seen = [], set()
    for d in dirs:
        for skill_dir in sorted(d.iterdir()):
            md = skill_dir / "SKILL.md"
            if not md.exists():
                continue
            s = _parse(md)
            if s and s.name not in seen:
                skills.append(s)
                seen.add(s.name)
    return skills

def _parse(path: Path) -> Skill | None:
    text = path.read_text()
    if text.startswith("---"):
        try:
            end = text.index("---", 3)
            fm = yaml.safe_load(text[3:end])
            return Skill(fm["name"], fm.get("description",""), text[end+3:].strip(), path)
        except Exception:
            pass
    lines = [l for l in text.splitlines() if l.strip()]
    if not lines:
        return None
    name = lines[0].lstrip("# ").strip() or path.parent.name
    desc = lines[1].strip() if len(lines) > 1 else ""
    return Skill(name, desc, text, path)

# Stage 1: discovery — chỉ inject name + description
def skills_to_system_prompt(skills: list[Skill]) -> str:
    if not skills:
        return ""
    return "## Skills\n" + "\n".join(f"- **{s.name}**: {s.description}" for s in skills)

# Stage 2: load body khi invoke
def load_skill_body(skill: Skill) -> str:
    return skill.body  # đã parse sẵn, chỉ cần dùng
`}