docs: clarify self-hosting for vendor-specific extensions and handlers

.github/ISSUE_TEMPLATE/enhancement-proposal.yml

@@ -3,6 +3,10 @@ description: This is a template for submitting an enhancement proposal.
 title: "[Proposal]: "
 labels: ["enhancement-proposal"]
 body:
+  - type: markdown
+    attributes:
+      value: |
+        > **Note:** The `Universal-Commerce-Protocol/ucp` repository only hosts vendor-neutral, cross-organization specifications and schemas under the `dev.ucp.*` namespace. Vendor- or organization-specific capabilities, extensions, and payment handlers (`com.{vendor}.*`, `org.{org}.*`) are **self-hosted** on your organization's domain and do not require an Enhancement Proposal or pull request to this repository. See [Namespace Governance](https://ucp.dev/latest/specification/overview/#namespace-governance) for details.
   - type: textarea
     id: summary
     attributes:

.github/ISSUE_TEMPLATE/feature-request.yml

@@ -2,6 +2,10 @@ name: Feature request
 description: Suggest an idea for this project
 title: "[Feat]: "
 body:
+  - type: markdown
+    attributes:
+      value: |
+        > **Note:** The `Universal-Commerce-Protocol/ucp` repository only hosts vendor-neutral, cross-organization specifications and schemas under the `dev.ucp.*` namespace. Vendor- or organization-specific capabilities, extensions, and payment handlers (`com.{vendor}.*`, `org.{org}.*`) are **self-hosted** on your organization's domain and do not require an issue or pull request in this repository. See [Namespace Governance](https://ucp.dev/latest/specification/overview/#namespace-governance) for details.
   - type: textarea
     id: problem
     attributes:

.github/pull_request_template.md

@@ -29,6 +29,7 @@ _Please select one or more categories that apply to this change._
 - [ ] I have added tests that prove my fix is effective or that my feature works.
 - [ ] New and existing unit tests pass locally with my changes.
 - [ ] (For Core/Capability) I have included/updated the relevant JSON schemas.
+- [ ] (For Core/Capability) Any new capability, extension, or payment handler is vendor-neutral (`dev.ucp.*`) rather than organization-specific (which should be [self-hosted](https://ucp.dev/latest/specification/overview/#namespace-governance) under the organization's reverse-domain namespace).
 - [ ] I have regenerated Python Pydantic models by running generate_models.sh under python_sdk.
 
 ## Screenshots / Logs (if applicable)

CONTRIBUTING.md

@@ -137,16 +137,29 @@ minor version of the core.
 
 ### Adding new extensions and capabilities to the core protocol
 
-UCP is designed to be extensible while keeping the core protocol light. A
-core principle of UCP is to ensure that the set of extensions and capabilities
-defined in UCP have broad ecosystem support. Vendors should first create
-capabilities & extensions in vendor-specific namespace pattern
-(e.g. com.{vendor}.\*) for new use cases. Requests to add new capabilities and
-extensions should only be submitted when there is proven widespread adoption of
-vendor-specific capabilities and extensions. See
-[Spec URL Binding](https://ucp.dev/specification/overview/#spec-url-binding)
-and [Governance Model](https://ucp.dev/specification/overview/#governance-model)
-for more details on using namespace pattern for creating vendor-specific
+UCP is designed to be extensible while keeping the core protocol light. A core
+principle of UCP is to ensure that the set of capabilities, extensions,
+services, and payment handlers defined in the core `dev.ucp.*` namespace have
+broad, cross-organization ecosystem support.
+
+**Self-Hosting Vendor-Specific Definitions:** The
+`Universal-Commerce-Protocol/ucp` repository only hosts core protocol
+specifications and schemas under `dev.ucp.*` (published at `ucp.dev`). You **do
+not** need to open a pull request to this repository to launch a vendor- or
+organization-specific capability, extension, service, or payment handler.
+Instead, define it under your organization's reverse-domain namespace (e.g.,
+`com.{vendor}.*`, `org.{org}.*`) and self-host its specification (`spec`) and
+JSON Schema (`schema`) URLs on your own domain.
+
+Requests to add new capabilities or extensions to `dev.ucp.*` should only be
+submitted when a capability is vendor-neutral and there is proven widespread
+adoption across multiple independent organizations. See
+[Namespace Governance](https://ucp.dev/latest/specification/overview/#namespace-governance)
+(specifically
+[Authority Binding](https://ucp.dev/latest/specification/overview/#authority-binding)
+and
+[Governance Model](https://ucp.dev/latest/specification/overview/#governance-model))
+for full details on reverse-domain namespaces and self-hosting vendor-specific
 capabilities and extensions.
 
 ### Code Reviews