feat: add secure multi-runtime controls

Make agent backends configurable and governable with encrypted credentials, explicit context sharing, and tool approval boundaries.

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

src/main/agent/runtime-controller.test.ts

@@ -0,0 +1,84 @@
+import { describe, expect, it, vi } from 'vitest'
+import type {
+  AgentEvent,
+  AgentRequest,
+  AgentRuntimeStatus
+} from '../../shared/contracts'
+import type { AgentRuntime } from './runtime'
+import { AgentRuntimeController } from './runtime-controller'
+
+class TestRuntime implements AgentRuntime {
+  readonly dispose = vi.fn(async () => {})
+  readonly started: Promise<void>
+  private release?: () => void
+  private markStarted!: () => void
+
+  constructor(
+    private readonly delayed = false,
+    readonly requiresToolApproval = false
+  ) {
+    this.started = new Promise((resolve) => {
+      this.markStarted = resolve
+    })
+  }
+
+  getStatus(): Promise<AgentRuntimeStatus> {
+    return Promise.resolve({
+      id: 'demo',
+      label: 'Test',
+      available: true,
+      detail: 'Test runtime'
+    })
+  }
+
+  async *run(
+    request: AgentRequest
+  ): AsyncGenerator<AgentEvent, void, void> {
+    this.markStarted()
+    if (this.delayed) {
+      await new Promise<void>((resolve) => {
+        this.release = resolve
+      })
+    }
+    yield {
+      requestId: request.requestId,
+      type: 'text',
+      delta: 'old runtime event'
+    }
+  }
+
+  finish(): void {
+    this.release?.()
+  }
+}
+
+describe('AgentRuntimeController', () => {
+  it('suppresses retired runtime events and disposes it after requests exit', async () => {
+    const previous = new TestRuntime(true, true)
+    const next = new TestRuntime()
+    const controller = new AgentRuntimeController(previous)
+    const authorize = vi.fn(async () => {})
+    const approvedStream = controller.run(
+      {
+        requestId: '1c608898-ecb7-4081-8174-2b6a52f53b08',
+        conversationId: 'conversation-2',
+        prompt: 'test'
+      },
+      new AbortController().signal,
+      authorize
+    )
+    const pendingEvent = approvedStream.next()
+    await previous.started
+    expect(authorize).toHaveBeenCalledWith(true)
+
+    const replacement = controller.replace(next)
+    previous.finish()
+
+    await expect(pendingEvent).resolves.toMatchObject({ done: true })
+    await replacement
+    expect(previous.dispose).toHaveBeenCalledOnce()
+    await expect(controller.getStatus()).resolves.toMatchObject({
+      label: 'Test'
+    })
+  })
+})