fix(server): convert mid-poll task errors and align config-error handling

Addresses review from @bhosmer-ant on #1769:

- handleAutomaticTaskPolling: wrap getTask in try/catch and convert
  ProtocolError(InvalidParams) to InternalError when a task vanishes
  mid-poll. A task going missing during automatic polling is a
  server-side issue — the client didn't request a task.
- handleAutomaticTaskPolling: change plain Error('No task store...') to
  ProtocolError(InternalError) for consistency with the analogous
  taskSupport config check at L177.
- Update three tests to assert error codes (not just messages) using
  toMatchObject, matching the pattern at L1824.

Follow-up (non-blocking): test coverage for the auto-polling output
validation path added in 3f29f35.

Author: felixweinberger

packages/server/src/server/mcp.ts

@@ -310,7 +310,7 @@ export class McpServer {
         ctx: ServerContext
     ): Promise<CallToolResult> {
         if (!ctx.task?.store) {
-            throw new Error('No task store provided for task-capable tool.');
+            throw new ProtocolError(ProtocolErrorCode.InternalError, 'No task store provided for task-capable tool.');
         }
 
         // Validate input and create task using the executor
@@ -324,7 +324,21 @@ export class McpServer {
 
         while (task.status !== 'completed' && task.status !== 'failed' && task.status !== 'cancelled') {
             await new Promise(resolve => setTimeout(resolve, pollInterval));
-            const updatedTask = await ctx.task.store.getTask(taskId);
+            let updatedTask;
+            try {
+                updatedTask = await ctx.task.store.getTask(taskId);
+            } catch (error) {
+                // RequestTaskStore.getTask throws InvalidParams when the task is
+                // missing, but a task vanishing mid-poll is a server-side issue
+                // (the client didn't even ask for a task) — surface as InternalError.
+                if (error instanceof ProtocolError && error.code === ProtocolErrorCode.InvalidParams) {
+                    throw new ProtocolError(
+                        ProtocolErrorCode.InternalError,
+                        `Task ${taskId} vanished during automatic polling`
+                    );
+                }
+                throw error;
+            }
             if (!updatedTask) {
                 throw new ProtocolError(ProtocolErrorCode.InternalError, `Task ${taskId} not found during polling`);
             }

test/integration/test/server/mcp.test.ts

@@ -1426,7 +1426,10 @@ describe('Zod v4', () => {
                         input: 'hello'
                     }
                 })
-            ).rejects.toThrow('Output validation error: Tool test has an output schema but no structured content was provided');
+            ).rejects.toMatchObject({
+                code: ProtocolErrorCode.InternalError,
+                message: expect.stringContaining('has an output schema but no structured content')
+            });
         });
         /***
          * Test: Tool with Output Schema Must Provide Structured Content
@@ -1548,7 +1551,10 @@ describe('Zod v4', () => {
                         input: 'hello'
                     }
                 })
-            ).rejects.toThrow(/Output validation error: Invalid structured content for tool test/);
+            ).rejects.toMatchObject({
+                code: ProtocolErrorCode.InternalError,
+                message: expect.stringMatching(/Invalid structured content for tool test/)
+            });
         });
 
         /***
@@ -6522,7 +6528,10 @@ describe('Zod v4', () => {
                     name: 'long-running-task',
                     arguments: { input: 'test data' }
                 })
-            ).rejects.toThrow(/requires task augmentation/);
+            ).rejects.toMatchObject({
+                code: ProtocolErrorCode.InvalidParams,
+                message: expect.stringMatching(/requires task augmentation/)
+            });
 
             taskStore.cleanup();
         });