test: cover executeIgnoringIncremental traced path and drop unused traceSync

The traced branch of `executeIgnoringIncremental` was not exercised by
any subscriber-attached test, tripping the 100% coverage threshold on
CI. Add a case in execute-diagnostics-test that subscribes to
`graphql:execute` and asserts start/end around a call.

Also drop the `traceSync` helper from diagnostics.ts; every call site
invokes `channel.traceSync(...)` directly, so the export was dead code.

Mark the `require('node:diagnostics_channel')` CJS fallback and the
enclosing `catch` block with c8 ignore comments — they are only
reachable on Node 20.0-20.15 (pre-`getBuiltinModule`) and on runtimes
without `diagnostics_channel` at all, neither of which the unit tests
run on.

Author: logaretm

src/diagnostics.ts

@@ -85,12 +85,14 @@ function resolveDiagnosticsChannel(): DiagnosticsChannelModule | undefined {
         }
       ).getBuiltinModule('node:diagnostics_channel');
     }
+    /* c8 ignore next 6 */
     if (!dc && typeof require === 'function') {
       // CJS fallback for runtimes that lack `process.getBuiltinModule`
       // (e.g. Node 20.0 - 20.15). ESM builds skip this branch because
       // `require` is undeclared there.
       dc = require('node:diagnostics_channel') as DiagnosticsChannelModule;
     }
+    /* c8 ignore next 3 */
   } catch {
     // diagnostics_channel not available on this runtime; tracing is a no-op.
   }
@@ -122,21 +124,6 @@ export const subscribeChannel: MinimalTracingChannel | undefined =
 export const resolveChannel: MinimalTracingChannel | undefined =
   dc?.tracingChannel('graphql:resolve');
 
-/**
- * Publish a synchronous operation through `channel`. Caller has already
- * verified that a subscriber is attached; this helper exists only so the
- * traced path doesn't need to be duplicated at every emission site.
- *
- * @internal
- */
-export function traceSync<T>(
-  channel: MinimalTracingChannel,
-  ctx: object,
-  fn: () => T,
-): T {
-  return channel.traceSync(fn, ctx);
-}
-
 /**
  * Publish a mixed sync-or-promise operation through `channel`. Caller has
  * already verified that a subscriber is attached.

src/execution/__tests__/execute-diagnostics-test.ts

@@ -13,6 +13,7 @@ import { buildSchema } from '../../utilities/buildASTSchema.js';
 import type { ExecutionArgs } from '../execute.js';
 import {
   execute,
+  executeIgnoringIncremental,
   executeSubscriptionEvent,
   executeSync,
   validateExecutionArgs,
@@ -78,6 +79,17 @@ describe('execute diagnostics channel', () => {
     expect(active.events.map((e) => e.kind)).to.deep.equal(['start', 'end']);
   });
 
+  it('emits start and end around executeIgnoringIncremental', () => {
+    active = collectEvents(executeChannel);
+
+    const document = parse('query Q { sync }');
+    // eslint-disable-next-line @typescript-eslint/no-floating-promises
+    executeIgnoringIncremental({ schema, document, rootValue });
+
+    expect(active.events.map((e) => e.kind)).to.deep.equal(['start', 'end']);
+    expect(active.events[0].ctx.operationName).to.equal('Q');
+  });
+
   it('emits start, error, and end when execute throws synchronously', () => {
     active = collectEvents(executeChannel);