feat: add mcp documentation skill for spec-aware development (#609)

Add a Claude Code skill (`.claude/skills/mcp-docs/`) that provides live
MCP documentation and specification context

## Motivation and Context
The modelcontextprotocol.io site provides both an [MCP
server](https://modelcontextprotocol.io/mcp) and an
[llms.txt](https://modelcontextprotocol.io/llms.txt) index for
machine-readable access to the documentation. This skill leverages both
to give Claude live access to the current spec during development.

## How Has This Been Tested?
The skill was evaluated on 3 realistic scenarios (implementation, code
review, spec question) comparing with-skill vs without-skill baseline:
- **Pass rate**: 100% vs 67% — skill consistently cites spec sources and
uses RFC 2119 language
- **Token efficiency**: 41% fewer tokens on average (44k vs 75k) — goes
directly to spec instead of reverse-engineering from codebase
- **Accuracy**: with-skill discovered URL mode elicitation (new in spec
2025-11-25) that baseline missed entirely
- **Description triggering**: optimized through 5 iterations of
automated trigger evaluation against 20 test prompts

## Breaking Changes
None

## Types of changes
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [x] Documentation update

## Checklist
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed

.claude/skills/mcp-docs/SKILL.md

@@ -0,0 +1,76 @@
+---
+name: mcp-docs
+description: >
+  Fetch live MCP specification and docs from modelcontextprotocol.io. Training data may be
+  outdated — default to using this skill when the query touches MCP protocol in any way.
+  Trigger for: implementing or debugging MCP features (sampling, elicitation, completion, tools,
+  resources, prompts, transports); SEPs or spec requirements; MCP transport behavior (SSE,
+  Streamable HTTP, reconnection, retry); authorization/OAuth; conformance test failures;
+  capability negotiation; message schemas. Skip only for pure Kotlin, build system, or
+  refactoring tasks with zero MCP protocol dependency. When in doubt, trigger.
+user_invocable: true
+---
+
+# MCP Documentation Skill
+
+Provides access to the official MCP specification and docs from modelcontextprotocol.io. The spec evolves faster than training data — always consult live documentation for protocol specifics like message schemas, required fields, capability negotiation, error handling, and transport requirements.
+
+## When to use
+
+**Proactively** (without being asked):
+- Implementing a feature defined in the MCP spec
+- Reviewing code that implements MCP protocol behavior
+- Fixing conformance test failures
+
+**On demand** (user asks or invokes `/mcp-docs`):
+- Questions about how a specific MCP feature works
+- Clarifying spec ambiguities
+- Looking up SEPs (Specification Enhancement Proposals)
+
+## How to fetch documentation
+
+### Strategy: MCP tool first, llms.txt fallback
+
+**Step 1 — Try the MCP search tool.** If `search_model_context_protocol` is available, use it:
+
+```
+search_model_context_protocol(query: "<your search query>")
+```
+
+One call, semantically ranked results. Fastest path.
+
+**Step 2 — Fallback to llms.txt + WebFetch.** If the MCP tool is not available:
+
+1. Fetch the documentation index:
+   ```
+   WebFetch("https://modelcontextprotocol.io/llms.txt", "Return the full content as-is")
+   ```
+
+2. Identify the relevant page URL(s) from the index. Key sections:
+   - **Specification**: `specification/...` — protocol details, message formats, transports, lifecycle
+   - **SEPs**: `seps/...` — specification enhancement proposals
+   - **Learning**: `docs/learn/...` — architecture, concepts
+   - **Development**: `docs/develop/...` — building clients/servers
+
+3. Fetch the specific page:
+   ```
+   WebFetch("<page-url>", "Return the full content of this documentation page")
+   ```
+
+### Version handling
+
+Always use the latest spec version by default. Only use a specific version or draft when the user explicitly requests it (e.g., "check the 2025-03-26 spec" or "what does the draft say").
+
+### Search guidance
+
+- Protocol message formats, required fields, capability negotiation → **Specification** section
+- Feature motivation, design rationale → relevant **SEP**
+- High-level concepts and architecture → **Learning** resources
+- Use your judgment on query count. A field-level question may need one page; implementing a feature may need 2-3.
+
+## Presenting information
+
+- **Always cite sources.** Include links to spec pages used: `(source: <url>)`
+- **Spec over training data** for specific protocol details (schemas, fields, error codes, capabilities). Training data is fine for general MCP concepts.
+- **Preserve RFC 2119 language.** The spec uses MUST/SHOULD/MAY — keep this distinction when explaining requirements.
+- **Be concise.** Focus on the details relevant to the user's task. Avoid dumping entire spec pages — extract what matters for the specific question or implementation at hand.

.gitignore

@@ -56,7 +56,7 @@ node_modules
 dist
 
 ### SWE agents ###
-.claude/
+.claude/settings.local.json
 .junie/
 
 ### Conformance test results ###