feat: MCP view of BM answers (absolute links, no material body by default)

- jz.bm.mcp-links on the token twins and the management API: under MCP,
  url and *_url strings starting with a single / get the app base
- material answers under MCP leave the body out unless include_body,
  marking it with body_omitted; write answers never echo it
- jz.bm.manage keys a dispatched call by user
- bm_materials and bm_material student tools
Plain HTTP answers are unchanged.

controllers/api/mcp_view.go

@@ -2,19 +2,84 @@ package api
 
 import (
 	"net/http"
+
+	"git.golem15.com/golem15/summercms/modules/bouncer"
 )
 
-// viaMCP reports whether r is an MCP tool call.
-func viaMCP(r *http.Request) bool { return false }
+// The MCP view of the material answers (D-17, D-21): a material's body may
+// hold transcript text, so an answer to an MCP tool call leaves it out
+// unless the call asks for it with include_body, and a write answer never
+// echoes it. Plain HTTP answers are unchanged.
 
-// includeBody reports whether r asks for the material body.
-func includeBody(r *http.Request) bool { return false }
+// viaMCP reports whether r is an MCP tool call: a request pier dispatched
+// in-process with the api_token marker. The marker lives on the context
+// only, so an HTTP request can never carry it.
+func viaMCP(r *http.Request) bool {
+	_, ok := bouncer.Dispatched(r.Context(), "api_token")
+	return ok
+}
 
-// materialView is the answer of GET /materials/{id} for r.
-func materialView(r *http.Request, d materialDetailJSON) any { return d }
+// includeBody reports whether r asks for the material body
+// (include_body=true or 1).
+func includeBody(r *http.Request) bool {
+	return flag(r, "include_body")
+}
 
-// managedMaterialView is a managed material for r.
-func managedMaterialView(r *http.Request, m managedMaterialJSON, write bool) any { return m }
+// bodyOmitted reports whether leaving body out hides content.
+func bodyOmitted(body *string) bool {
+	return body != nil && *body != ""
+}
 
-// managedMaterialDetailView is a managed material with its files for r.
-func managedMaterialDetailView(r *http.Request, d managedMaterialDetailJSON, write bool) any { return d }
+// mcpMaterialDetailJSON is a published material under MCP without its body:
+// the list fields and the files, with body_omitted when a non-empty body was
+// left out. Body shadows the embedded one and stays nil.
+type mcpMaterialDetailJSON struct {
+	materialDetailJSON
+	Body        *string `json:"body,omitempty"`
+	BodyOmitted bool    `json:"body_omitted,omitempty"`
+}
+
+// mcpManagedMaterialJSON is a managed material under MCP without its body.
+type mcpManagedMaterialJSON struct {
+	managedMaterialJSON
+	Body        *string `json:"body,omitempty"`
+	BodyOmitted bool    `json:"body_omitted,omitempty"`
+}
+
+// mcpManagedMaterialDetailJSON is a managed material with its files under
+// MCP without its body.
+type mcpManagedMaterialDetailJSON struct {
+	mcpManagedMaterialJSON
+	Files []fileJSON `json:"files"`
+}
+
+// materialView is the answer of GET /materials/{id} (student): unchanged
+// over plain HTTP; under MCP (mcp) without the body unless withBody.
+func materialView(d materialDetailJSON, mcp, withBody bool) any {
+	if !mcp || withBody {
+		return d
+	}
+	return mcpMaterialDetailJSON{materialDetailJSON: d, BodyOmitted: bodyOmitted(d.Body)}
+}
+
+// managedMaterialView is a managed material: unchanged over plain HTTP;
+// under MCP (mcp) without the body unless withBody (a write answer passes
+// false, so it never echoes the body).
+func managedMaterialView(m managedMaterialJSON, mcp, withBody bool) any {
+	if !mcp || withBody {
+		return m
+	}
+	return mcpManagedMaterialJSON{managedMaterialJSON: m, BodyOmitted: bodyOmitted(m.Body)}
+}
+
+// managedMaterialDetailView is a managed material with its files, under the
+// same rule as managedMaterialView.
+func managedMaterialDetailView(d managedMaterialDetailJSON, mcp, withBody bool) any {
+	if !mcp || withBody {
+		return d
+	}
+	return mcpManagedMaterialDetailJSON{
+		mcpManagedMaterialJSON: mcpManagedMaterialJSON{managedMaterialJSON: d.managedMaterialJSON, BodyOmitted: bodyOmitted(d.Body)},
+		Files:                  d.Files,
+	}
+}