Add approaches doc

docs/approaches.md

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+# Approaches Being Explored
+
+> These are not mutually exclusive solutions.
+
+## 1. Skills as MCP Primitives
+
+Add Agent Skills as a first-class, discoverable primitive in MCP. A skill is a named bundle of instructions plus references to tools, prompts, and resources that together teach an agent how to perform a domain-specific workflow.
+
+**Proposal:** [SEP-2076](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2076)
+
+**Author:** [Yu Yi](https://github.com/erain)
+
+## 2. Skills as Registry Metadata
+
+Add skill references to MCP registry entries so users know to install associated skills alongside servers.
+
+**Implementations:** 
+- [Ozz](https://github.com/JAORMX) started a discussion around [skills.json format proposal](https://github.com/modelcontextprotocol/registry/discussions/895)
+- NimbleBrain has implemented this via a `skill` field in registry `_meta`, supporting `.skill` artifact bundles (ZIP containing SKILL.md + manifest.json).
+    - https://github.com/NimbleBrainInc/skills
+    - [registry.nimbletools.ai](https://registry.nimbletools.ai/)
+
+## 3. Skills as Tools
+
+Expose skills via tools like `list_skills` and `read_skills`. Server instructions can direct the agent to call the skill tool first.
+
+**Implementations:** 
+
+- [skilljack-mcp](https://github.com/olaservo/skilljack-mcp)
+- [skills-over-mcp](https://github.com/keithagroves/skills-over-mcp)
+
+This approach may also:
+
+- Expose skills as MCP resources
+- Use Prompts for explicit skill invocation
+- Use `tools/listChanged` and other notifications for dynamic updates without server re-initialization
+
+### Variant: Skills via Sampling
+
+Instead of exposing skill tools to the main agent, use MCP's Sampling with Tools capability ([SEP-1577](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/1577)). The server requests a sampling call with skill-specific tools (`read_skill_md`, `execute_script`, etc.) that are only visible during that sampling request. This keeps skill tools hidden from the main agent, addressing tool bloat. The server orchestrates skill execution; the main agent just sees the result.
+
+**Caveat:** Sampling has limited client support currently.
+
+**Source:** [jbnitorum](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2076#issuecomment-3806151745)
+
+## 4. Gateway/Composition Pattern
+
+A gateway-style server that provides a group of MCPs as one, ensuring they get requisite configuration and instructions to work in harmony.
+
+This pattern could enable loading primitives (tools) without the full "server" boundary.
+
+**Community input:**
+
+> "MCP repos can also be used as libraries... a gateway in same language as bundle servers could also load primitives like tools, and not necessarily need or want the 'server' parts." [SamMorrowDrums](https://github.com/SamMorrowDrums)
+
+## 5. Server Instructions Reference
+
+Use server instructions as a pointer to a resource: "If you need to do X, fetch resource Y for further instructions." This defers loading skill content until needed, managing context more efficiently.
+
+**Limitation:** May not work with off-the-shelf servers where you can't modify their instructions.
+
+## 6. Official Convention as Intermediate Step
+
+A documented "MCP Skills Convention" as a middle path between ad-hoc experiments and protocol extension. This could:
+
+- Define well-known URI schemes or naming patterns (e.g., resources matching `**/SKILL.md`)
+- Recommend metadata structure (version, tags, dependencies) aligned with agentskills.io
+- Provide guidance on control model: resources for application-controlled, `skill()` tool for model-controlled
+- Be documented in MCP docs as a "Pattern" — not in protocol schema, but officially recommended
+- Allow data gathering on adoption before considering protocol-level changes
+
+This mirrors how other ecosystems (e.g., Kubernetes) graduate patterns: start as convention, prove value, then formalize. Could be a concrete IG deliverable: "MCP Skills Convention v0.1."