feat: customize model provider requests

Model connections can now save bounded JSON request headers and top-level body fields. Direct requests and Continue support both; local OpenCode and DeepSeek Harness use only native header support, while the managed remote OpenCode gateway applies both.

Runtime, protocol, and authentication fields keep precedence. Custom values are ordinary connection settings, not credential storage. This migrates Runtime settings from v20 to v21 and updates the DeepSeek control and managed Runtime ACP capabilities.

Release note: 模型连接详情新增自定义请求头和请求体；直连与 Continue 支持两者，本地 OpenCode 和 DeepSeek Harness 仅应用原生支持的请求头，受管远程 OpenCode 支持两者，界面会明确提示生效范围。

src/main/agent/deepseek-harness-acp-e2e.test.ts

@@ -33,6 +33,8 @@ import {
 import { GOODBUDDY_HARNESS_MAX_STEP_TOKENS } from './goodbuddy-harness-control-plane'
 import { DshNpmExtensionInstaller } from './dsh-extension-marketplace'
 import { DEEPSEEK_HARNESS_MAX_FRAME_BYTES } from './deepseek-harness-control-protocol'
+import { createOpenAIChatCompletionsUrl } from './openai-endpoint'
+import { createModelRequestProbe } from '../../../tests/support/model-request-probe'
 
 const CREDENTIAL_REF = 'GOODBUDDY_HARNESS_MODEL_API_KEY'
 const SKILL_CALL_ID = 'e2e-skill-call'
@@ -329,6 +331,7 @@ function createInProcessLaunch(
         provider: 'goodbuddy',
         model: options.model,
         supportsImageInput: options.supportsImageInput,
+        requestHeaders: options.requestHeaders,
         harnessVersion: '0.1.0-rc.8',
         credentialRefs: options.credentialRefs,
         skillPackages: options.skillPackages,
@@ -891,6 +894,79 @@ describe('DeepSeek Harness real ACP control-plane E2E', () => {
     60_000
   )
 
+  it.runIf(liveModelEnabled)(
+    'forwards a custom model header through the real DeepSeek Harness provider',
+    async () => {
+      if (!liveApiKey) {
+        throw new Error(
+          'GOODBUDDY_DSH_API_KEY is required for live DSH model E2E'
+        )
+      }
+      const root = await realpath(
+        await mkdtemp(join(tmpdir(), 'goodbuddy-harness-header-model-'))
+      )
+      const workspace = join(root, 'workspace')
+      const dshHome = join(root, 'dsh-home')
+      await Promise.all([mkdir(workspace), mkdir(dshHome)])
+      const probe = await createModelRequestProbe({
+        upstreamUrl: createOpenAIChatCompletionsUrl(liveBaseUrl),
+        headerName: 'x-goodbuddy-e2e'
+      })
+      const inProcess = createInProcessLaunch(dshHome)
+      const runtime = new DeepSeekHarnessRuntime({
+        defaultWorkspace: workspace,
+        baseUrl: probe.baseUrl,
+        model: liveModel,
+        requestHeaders: {
+          'x-goodbuddy-e2e': 'harness-header-present'
+        },
+        launch: (options) => inProcess.launch(options),
+        credentialRefs: {
+          [CREDENTIAL_REF]: liveApiKey
+        },
+        initializationTimeoutMs: 20_000,
+        promptTimeoutMs: 120_000,
+        shutdownTimeoutMs: 5_000
+      })
+
+      try {
+        const events = await collect(
+          runtime.run(
+            {
+              requestId: 'request-live-custom-header',
+              conversationId: 'live-custom-header',
+              prompt:
+                'Reply with exactly DSH_CUSTOM_HEADER_E2E_OK and nothing else.',
+              workMode: 'ask'
+            },
+            new AbortController().signal
+          )
+        )
+        expect(
+          events
+            .flatMap((event) =>
+              event.type === 'text' ? [event.delta] : []
+            )
+            .join('')
+        ).toContain('DSH_CUSTOM_HEADER_E2E_OK')
+        expect(probe.observations).toEqual([
+          {
+            headerValue: 'harness-header-present',
+            bodyFields: {}
+          }
+        ])
+      } finally {
+        await runtime.dispose()
+        await Promise.allSettled(
+          inProcess.hosts.map((host) => host.dispose())
+        )
+        await probe.close()
+        await rm(root, { recursive: true, force: true })
+      }
+    },
+    180_000
+  )
+
   it.runIf(liveModelEnabled)(
     'lets a real model use Main-brokered Web Search and Fetch in Ask',
     async () => {