test(sdk): enforce runtime bridge seam and explicit no-fallback behavior

sdk/src/gsd-transport.test.ts

@@ -234,6 +234,32 @@ describe('GSDTransport', () => {
     expect(adapters.execSubprocessJson).toHaveBeenCalledOnce();
   });
 
+  it('fails when command is unregistered and subprocess fallback is disabled', async () => {
+    const registry = new QueryRegistry();
+
+    const adapters = {
+      dispatchNative: vi.fn(async () => ({ data: { ok: true } })),
+      execSubprocessJson: vi.fn(async () => ({ ok: 'fallback' })),
+      execSubprocessRaw: vi.fn(async () => 'fallback-raw'),
+    };
+
+    const transport = new GSDTransport(registry, adapters);
+
+    await expect(transport.run({
+      legacyCommand: 'unknown',
+      legacyArgs: [],
+      registryCommand: 'unknown',
+      registryArgs: [],
+      mode: 'json',
+      projectDir: '/tmp',
+    }, {
+      preferNative: true,
+      allowFallbackToSubprocess: false,
+    })).rejects.toThrow("Subprocess fallback disabled");
+
+    expect(adapters.execSubprocessJson).not.toHaveBeenCalled();
+  });
+
   it('forces raw subprocess path when workstream present and mode is raw', async () => {
     const registry = new QueryRegistry();
     registry.register('commit', async () => ({ data: { hash: 'abc' } }));

sdk/src/gsd-transport.ts

@@ -2,6 +2,7 @@ import type { QueryResult } from './query/utils.js';
 import type { QueryRegistry } from './query/registry.js';
 import type { TransportMode } from './gsd-transport-policy.js';
 import { toFailureSignal } from './query-failure-classification.js';
+import { GSDToolsError } from './gsd-tools-error.js';
 
 export interface TransportRequest {
   legacyCommand: string;
@@ -52,7 +53,16 @@ export class GSDTransport {
         onDecision?.({ dispatchMode: 'subprocess', reason: 'native_failure_fallback' });
       }
     } else {
-      onDecision?.({ dispatchMode: 'subprocess', reason: this.subprocessReason(request, policy) });
+      const reason = this.subprocessReason(request, policy);
+      onDecision?.({ dispatchMode: 'subprocess', reason });
+      if (!policy.allowFallbackToSubprocess) {
+        throw GSDToolsError.failure(
+          `Subprocess fallback disabled: command '${request.registryCommand}' cannot run without native dispatch`,
+          request.legacyCommand,
+          request.legacyArgs,
+          null,
+        );
+      }
     }
 
     return this.dispatchSubprocess(request);

sdk/src/query-runtime-seam-coverage.test.ts

@@ -0,0 +1,20 @@
+import { describe, it, expect, vi } from 'vitest';
+import { createGSDToolsRuntime } from './query-gsd-tools-runtime.js';
+
+describe('SDK Runtime Bridge seam coverage', () => {
+  it('exposes bridge as the single runtime seam', () => {
+    const runtime = createGSDToolsRuntime({
+      projectDir: '/tmp/project',
+      gsdToolsPath: '/tmp/gsd-tools.cjs',
+      timeoutMs: 1_000,
+      shouldUseNativeQuery: () => true,
+      execJsonFallback: vi.fn(async () => ({})),
+      execRawFallback: vi.fn(async () => ''),
+    });
+
+    expect(Object.keys(runtime)).toEqual(['bridge']);
+    expect(typeof runtime.bridge.resolve).toBe('function');
+    expect(typeof runtime.bridge.execute).toBe('function');
+    expect(typeof runtime.bridge.dispatchHotpath).toBe('function');
+  });
+});