fix(vscode): avoid writing null agent config fields

Omit unset agent fields on create
Delete cleared agent fields in VS Code config updates
Cover null field removal with a regression test

packages/ui/src/stores/useAgentsStore.ts

@@ -177,6 +177,8 @@ const SLOW_HEALTH_POLL_BASE_MS = 800;
 const SLOW_HEALTH_POLL_INCREMENT_MS = 200;
 const SLOW_HEALTH_POLL_MAX_MS = 2000;
 
+const hasValue = <T>(value: T | null | undefined): value is T => value !== null && value !== undefined;
+
 export interface AgentDraft {
   name: string;
   scope: AgentScope;
@@ -345,8 +347,8 @@ export const useAgentsStore = create<AgentsStore>()(
             if (config.description) agentConfig.description = config.description;
             if (config.model) agentConfig.model = config.model;
             if (config.variant) agentConfig.variant = config.variant;
-            if (config.temperature !== undefined) agentConfig.temperature = config.temperature ?? null;
-            if (config.top_p !== undefined) agentConfig.top_p = config.top_p ?? null;
+            if (hasValue(config.temperature)) agentConfig.temperature = config.temperature;
+            if (hasValue(config.top_p)) agentConfig.top_p = config.top_p;
             if (config.prompt) agentConfig.prompt = config.prompt;
             if (config.permission) agentConfig.permission = config.permission;
             if (config.disable !== undefined) agentConfig.disable = config.disable;

packages/vscode/src/bridge-config-runtime.test.js

@@ -52,6 +52,39 @@ afterEach(() => {
 const readJson = (filePath) => JSON.parse(fs.readFileSync(filePath, 'utf8'));
 
 describe('VS Code config bridge plugin parity', () => {
+  test('removes agent fields when update payload sends null', async () => {
+    const root = fs.mkdtempSync(path.join(os.tmpdir(), 'openchamber-vscode-agent-null-'));
+    tempRoots.push(root);
+    const ctx = createCtx(root);
+    const configDir = path.join(root, '.opencode');
+    const configPath = path.join(configDir, 'opencode.json');
+    fs.mkdirSync(configDir, { recursive: true });
+    fs.writeFileSync(configPath, JSON.stringify({
+      agent: {
+        build: {
+          variant: 'fast',
+          temperature: 0.3,
+          top_p: 0.8,
+          mode: 'subagent',
+        },
+      },
+    }, null, 2), 'utf8');
+
+    const updated = await handleConfigBridgeMessage({
+      id: 'update-agent-null-fields',
+      type: 'api:config/agents',
+      payload: {
+        method: 'PATCH',
+        name: 'build',
+        directory: root,
+        body: { variant: null, temperature: null, top_p: null },
+      },
+    }, ctx, deps);
+
+    expect(updated?.success).toBe(true);
+    expect(readJson(configPath).agent.build).toEqual({ mode: 'subagent' });
+  });
+
   test('creates, lists, updates, and deletes project plugin entries', async () => {
     const root = fs.mkdtempSync(path.join(os.tmpdir(), 'openchamber-vscode-plugins-'));
     tempRoots.push(root);

packages/vscode/src/opencodeConfig.ts

@@ -1605,12 +1605,30 @@ export const createAgent = (agentName: string, config: Record<string, unknown>,
   }
 
   // Extract scope and prompt from config - scope is only used for path determination, not written to file
-  const { prompt, scope: _ignored, ...frontmatter } = config as Record<string, unknown> & { prompt?: unknown; scope?: unknown };
+  const { prompt, scope: _ignored, ...rawFrontmatter } = config as Record<string, unknown> & { prompt?: unknown; scope?: unknown };
   void _ignored; // Scope is only used for path determination
+  const frontmatter = Object.fromEntries(
+    Object.entries(rawFrontmatter).filter(([, value]) => value !== null && value !== undefined)
+  );
   writeMdFile(targetPath, frontmatter, typeof prompt === 'string' ? prompt : '');
   resetAgentLookupCache(globalAgentLookupCache);
 };
 
+const deleteAgentJsonField = (config: Record<string, unknown>, agentName: string, field: string): boolean => {
+  const agentMap = config.agent as Record<string, unknown> | undefined;
+  const current = agentMap?.[agentName] as Record<string, unknown> | undefined;
+  if (!agentMap || !current || !(field in current)) return false;
+
+  delete current[field];
+  if (Object.keys(current).length === 0) {
+    delete agentMap[agentName];
+  }
+  if (Object.keys(agentMap).length === 0) {
+    delete config.agent;
+  }
+  return true;
+};
+
 export const updateAgent = (agentName: string, updates: Record<string, unknown>, workingDirectory?: string) => {
   ensureDirs();
 
@@ -1757,6 +1775,19 @@ export const updateAgent = (agentName: string, updates: Record<string, unknown>,
     const hasMdField = Boolean(mdData?.frontmatter?.[field] !== undefined);
     const hasJsonField = Boolean(jsonSection?.[field] !== undefined);
 
+    if (value === null) {
+      if (hasMdField && mdData) {
+        delete mdData.frontmatter[field];
+        mdModified = true;
+      }
+
+      if (hasJsonField && deleteAgentJsonField(config, agentName, field)) {
+        jsonModified = true;
+      }
+
+      continue;
+    }
+
     // JSON takes precedence over md, so update JSON first if field exists there
     if (hasJsonField) {
       if (!config.agent) config.agent = {};

packages/web/server/lib/opencode/agents.js

@@ -409,7 +409,10 @@ function createAgent(agentName, config, workingDirectory, scope) {
     targetScope = AGENT_SCOPE.USER;
   }
 
-  const { prompt, scope: _scopeFromConfig, ...frontmatter } = config;
+  const { prompt, scope: _scopeFromConfig, ...rawFrontmatter } = config;
+  const frontmatter = Object.fromEntries(
+    Object.entries(rawFrontmatter).filter(([, value]) => value !== null && value !== undefined)
+  );
 
   writeMdFile(targetPath, frontmatter, prompt || '');
   console.log(`Created new agent: ${agentName} (scope: ${targetScope}, path: ${targetPath})`);