feature: Add support for Session-specific Resource Templates (SessionWithResourceTemplates)

[MarianaGiraldoL]

Problem Statement

Currently, MCP allows registering session-specific tools and static resources using SessionWithTools and SessionWithResources.
However, there’s no equivalent support for resource templates, and attempts to add one fail due to URI validation in AddSessionResources, resulting in: invalid resource URI:

Proposed Solution

Introduce support for session-specific resource templates, e.g. SessionWithResourceTemplates, analogous to the existing SessionWithTools and SessionWithResources.

This would allow handlers that define ResourceTemplates visible only within a single session.

Example Usage

// Add a session resource template
newResourceTemplate := mcp.NewResourceTemplate(
    resourceURI,
    resourceName,
    mcp.WithTemplateDescription(resourceDescription),
    mcp.WithTemplateMIMEType(resourceMIMEType),
)

err := s.AddSessionResourceTemplate(
    sessionID,
    newResourceTemplate,
    func(ctx context.Context, request mcp.ReadResourceRequest) ([]mcp.ResourceContents, error) {
        // This handler is only available to this specific session
        return []mcp.ResourceContents{
            mcp.TextResourceContents{
                URI:      request.Params.URI,
                MIMEType: "application/json",
                Text:     "Example result text",
            },
        }, nil
    },
)
if err != nil {
    log.Printf("Failed to add session resource template: %v", err)
}

---

Rationale / Benefits

• Enables session-scoped resource templates (parity with tools/resources).
• Simplifies dynamic per-session configuration of resource templates.
• Avoids URI validation errors for session-bound contexts.