fix(core): exclude fragment delimiter from URI template matches

.changeset/uri-template-fragment-delimiter.md

@@ -0,0 +1,5 @@
+---
+'@modelcontextprotocol/core': patch
+---
+
+Match URI template fragment expressions with their required `#` delimiter outside the captured variable, including empty fragment values.

packages/core-internal/src/shared/uriTemplate.ts

@@ -230,11 +230,14 @@ export class UriTemplate {
                 pattern = part.exploded ? '([^/,]+(?:,[^/,]+)*)' : '([^/,]+)';
                 break;
             }
-            case '+':
-            case '#': {
+            case '+': {
                 pattern = '(.+)';
                 break;
             }
+            case '#': {
+                pattern = '#(.*)';
+                break;
+            }
             case '.': {
                 pattern = String.raw`\.([^/,]+)`;
                 break;

packages/core-internal/test/shared/uriTemplate.test.ts

@@ -51,6 +51,21 @@ describe('UriTemplate', () => {
             expect(template.expand({ var: '/test' })).toBe('X#/test');
             expect(template.variableNames).toEqual(['var']);
         });
+
+        it.each(['intro', '/chapter?view=full', ''])('should match fragment value %j without its delimiter', section => {
+            const template = new UriTemplate('file:///doc{#section}');
+            expect(template.match(template.expand({ section }))).toEqual({ section });
+        });
+
+        it('should reject a fragment value without the fragment delimiter', () => {
+            const template = new UriTemplate('file:///doc{#section}');
+            expect(template.match('file:///docintro')).toBeNull();
+        });
+
+        it('should preserve reserved expansion matching without a fragment delimiter', () => {
+            const template = new UriTemplate('file:///doc{+section}');
+            expect(template.match('file:///docintro')).toEqual({ section: 'intro' });
+        });
     });
 
     describe('label expansion', () => {