fix(inventory): preserve instructions in ForMCPRequest incl. server/discover

ForMCPRequest dropped the generated instructions when narrowing the per-request
inventory, so HTTP server/discover (and initialize) returned empty instructions
even though the full inventory had them. Preserve instructions on the copy and
treat server/discover like initialize. Fixes discover<->initialize parity flagged
on go-sdk#1034 (root cause was here, not the SDK).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Copilot

pkg/inventory/registry.go

@@ -71,6 +71,7 @@ func (r *Inventory) UnrecognizedToolsets() []string {
 // MCP method constants for use with ForMCPRequest.
 const (
 	MCPMethodInitialize             = "initialize"
+	MCPMethodDiscover               = "server/discover"
 	MCPMethodToolsList              = "tools/list"
 	MCPMethodToolsCall              = "tools/call"
 	MCPMethodResourcesList          = "resources/list"
@@ -89,7 +90,7 @@ const (
 //   - itemName: Name of specific item for call/get methods (tool name, resource URI, or prompt name)
 //
 // Returns a new Registry containing only the items relevant to the request:
-//   - MCPMethodInitialize: Empty (capabilities are set via ServerOptions, not registration)
+//   - MCPMethodInitialize / MCPMethodDiscover: Empty items (capabilities from ServerOptions; instructions preserved)
 //   - MCPMethodToolsList: All available tools (no resources/prompts)
 //   - MCPMethodToolsCall: Only the named tool
 //   - MCPMethodResourcesList, MCPMethodResourcesTemplatesList: All available resources (no tools/prompts)
@@ -114,6 +115,7 @@ func (r *Inventory) ForMCPRequest(method string, itemName string) *Inventory {
 		featureChecker:       r.featureChecker,
 		filters:              r.filters, // shared, not modified
 		unrecognizedToolsets: r.unrecognizedToolsets,
+		instructions:         r.instructions, // server identity; preserved for all methods
 	}
 
 	// Helper to clear all item types
@@ -124,7 +126,10 @@ func (r *Inventory) ForMCPRequest(method string, itemName string) *Inventory {
 	}
 
 	switch method {
-	case MCPMethodInitialize:
+	case MCPMethodInitialize, MCPMethodDiscover:
+		// Both handshakes register no items; capabilities come from ServerOptions
+		// and instructions are preserved via the copy above (SEP-2575 discover
+		// must surface the same server identity as initialize).
 		clearAll()
 	case MCPMethodToolsList:
 		result.resourceTemplates, result.prompts = nil, nil

pkg/inventory/registry_test.go

@@ -2268,3 +2268,16 @@ func TestShouldStripMCPAppsMetadata(t *testing.T) {
 		})
 	}
 }
+
+func TestForMCPRequest_PreservesInstructions(t *testing.T) {
+	reg := mustBuild(t, NewBuilder().
+		SetTools([]ServerTool{mockTool("tool1", "repos", true)}).
+		WithToolsets([]string{"all"}).
+		WithServerInstructions())
+	want := reg.Instructions()
+	require.NotEmpty(t, want, "expected base inventory to generate instructions")
+	for _, m := range []string{MCPMethodDiscover, MCPMethodInitialize, MCPMethodToolsList} {
+		require.Equal(t, want, reg.ForMCPRequest(m, "").Instructions(),
+			"instructions must be preserved for %s (server identity)", m)
+	}
+}