docs: align Skills corrections with the final SEP and website (#147)

The stable Skills page missed the final SEP's Agent Skills compatibility
clause, and its examples used abbreviated hashes and inconsistent byte
sizes. Archived drafts also retained current-sounding source-of-truth
guidance.

This corrects the stable page directly to match already-established
requirements: restores the compatibility clause, shows the resources
capability and server/discover, explains omitted request metadata, and
makes the example manifests and content consistent. It also labels
archived documents as historical and fixes the SEP domain in AGENTS.md.
This is an editorial alignment, not a new extension proposal; #142
remains separate.

Validation: all JSON examples parsed; all 13 manifest entries checked
against sample bytes for SHA-256 and size; the corrected specification
builds with the VitePress publishing site; git diff --check passed.

AI assistance: prepared with Codex.

docs/archive/agent-plugins-analysis.md

@@ -1,5 +1,7 @@
 # Agent Plugins x Skills Over MCP
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 ## Summary
 
 Agent Plugins 1.0 is a portable *packaging* format — a directory with a `plugin.json` manifest whose two component types are Agent Skills (a `skills/` directory) and MCP server configurations (`mcp.json`). It deliberately layers on top of the Agent Skills spec and MCP rather than redefining either, so it is overwhelmingly a **complement** to SEP-2640: the SEP moves skills over the wire at runtime; Agent Plugins moves them onto disk at install time. The two even compose — a plugin's `mcp.json` can point at a server that itself serves skills under the extension.

docs/archive/approaches.md

@@ -1,5 +1,7 @@
 # Approaches Being Explored
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 > ℹ️ The design space has largely converged on the convention approach (Approach 6), now formalized as [SEP-2640](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2640). This document is kept as a map of the alternatives that were considered; for the current direction, see the SEP.
 
 > These are not mutually exclusive solutions.

docs/archive/experimental-findings.md

@@ -1,5 +1,7 @@
 # Experimental Findings
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 > ℹ️ **This document is not actively maintained.** It captures a snapshot of early findings. Current discussion and decisions are tracked in the [meeting notes discussions](https://github.com/modelcontextprotocol/modelcontextprotocol/discussions/categories/meeting-notes-skills-over-mcp-wg), [Discord #skills-over-mcp-wg](https://discord.com/channels/1358869848138059966/1464745826629976084), and on the [SEP-2640 PR](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2640).
 
 > **Contributing findings?** Start with the [experimental findings template](findings-template.md).

docs/archive/findings-template.md

@@ -1,5 +1,7 @@
 # Experimental Findings Template
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 Use this template when adding an entry to [experimental-findings.md](experimental-findings.md). Include enough evidence for another contributor to evaluate the result, and write "Not documented" rather than inferring missing details.
 
 ---

docs/archive/glossary.md

@@ -1,5 +1,7 @@
 # Glossary
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 This glossary defines working terminology for the Skills Over MCP documents. It is descriptive rather than normative: the [MCP specification](https://modelcontextprotocol.io/specification/2025-11-25/server/resources) and the [Agent Skills specification](https://agentskills.io/specification) remain the source of truth for their respective formats and protocol surfaces. Definitions are intentionally short (1–3 sentences) and note alignment or divergence with Agent Skills where relevant.
 
 ## Core terms

docs/archive/open-questions.md

@@ -1,5 +1,7 @@
 # Open Questions
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 > ℹ️ **This document is not actively maintained.** It captures a snapshot of early discussion. Current open questions and decisions are tracked in the [meeting notes discussions](https://github.com/modelcontextprotocol/modelcontextprotocol/discussions/categories/meeting-notes-skills-over-mcp-wg), [Discord #skills-over-mcp-wg](https://discord.com/channels/1358869848138059966/1464745826629976084), and on the [SEP-2640 PR](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2640).
 
 ## 1. Is this a registry problem or an MCP server problem?

docs/archive/problem-statement.md

@@ -1,5 +1,7 @@
 # Problem Statement
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 [Agent Skills](https://agentskills.io/home) support in AI applications demonstrates demand for rich workflow instructions, but there's no convention for exposing equivalent functionality through MCP primitives.
 
 ## Current Limitations

docs/archive/related-work.md

@@ -1,5 +1,7 @@
 # Related Work
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 ## SEPs and Proposals
 
 | Proposal | Venue | Description |

docs/archive/sep-draft-skills-extension.md

@@ -1,5 +1,7 @@
 # SEP-2640: Skills Extension
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 - **Status**: Draft
 - **Type**: Extensions Track
 - **Created**: 2026-04-23

docs/archive/skill-meta-keys.md

@@ -1,5 +1,7 @@
 # Using `_meta` for Skill Resources
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 > Guidelines for structured metadata on skill resources served over MCP.
 
 **Issue:** [#55](https://github.com/modelcontextprotocol/experimental-ext-skills/issues/55)

docs/archive/skill-uri-scheme.md

@@ -1,5 +1,7 @@
 # Skill URI Scheme Proposal
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 > Proposed convention for identifying skill resources over MCP.
 
 **Issue:** [#44](https://github.com/modelcontextprotocol/experimental-ext-skills/issues/44)

docs/archive/threat-model.md

@@ -1,5 +1,7 @@
 # Threat Model: Skills Over MCP
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 > ⚠️ **Experimental** — This document models threats against skills served over MCP as specified in [SEP-2640](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2640) *in its current form*: the revision on the canonical [`sep/skills-extension`](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2640/files) branch, which supersedes the older [`docs/sep-draft-skills-extension.md`](sep-draft-skills-extension.md) working draft. That revision **replaced the `skill://index.json` resource with the `skills/list` and `skills/get` methods, added a per-file `resources` digest array covering the whole skill, and moved archive distribution to a deferred-features appendix.** It is a Working Group reference, not a normative part of the SEP. Where it recommends behavior beyond what SEP-2640 mandates, it says so.
 
 ## Scope

docs/archive/use-cases.md

@@ -1,5 +1,7 @@
 # Use Cases
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 ## 1. Complex Workflow Orchestration
 
 Skills that teach agents how to perform multi-step workflows that they wouldn't know how to execute from tool descriptions alone.

docs/archive/why-and-when.md

@@ -1,5 +1,7 @@
 # Why Skills Over MCP?
 
+> **Historical document.** Frozen during development of SEP-2640; statements of current status and requirements below describe that draft-era context. See the [stable specification](../../specification/stable/skills.mdx) for current requirements and the [archive index](README.md) for context.
+
 > The value proposition for distributing agent skills through MCP, and a guide for when it applies.
 
 ## The Gap Between Tools and Know-How