feat: make systemDefaultModel optional for OpenCode fallback

src/agents/atlas.ts

@@ -523,9 +523,6 @@ function buildDynamicOrchestratorPrompt(ctx?: OrchestratorContext): string {
 }
 
 export function createAtlasAgent(ctx: OrchestratorContext): AgentConfig {
-  if (!ctx.model) {
-    throw new Error("createAtlasAgent requires a model in context")
-  }
   const restrictions = createAgentToolRestrictions([
     "task",
     "call_omo_agent",
@@ -534,7 +531,7 @@ export function createAtlasAgent(ctx: OrchestratorContext): AgentConfig {
     description:
       "Orchestrates work via delegate_task() to complete ALL tasks in a todo list until fully done",
     mode: "primary" as const,
-    model: ctx.model,
+    ...(ctx.model ? { model: ctx.model } : {}),
     temperature: 0.1,
     prompt: buildDynamicOrchestratorPrompt(ctx),
     thinking: { type: "enabled", budgetTokens: 32000 },

src/agents/utils.test.ts

@@ -106,6 +106,30 @@ describe("createBuiltinAgents with model overrides", () => {
    })
 })
 
+describe("createBuiltinAgents without systemDefaultModel", () => {
+  test("creates agents successfully without systemDefaultModel", async () => {
+    // #given - no systemDefaultModel provided
+
+    // #when
+    const agents = await createBuiltinAgents([], {}, undefined, undefined)
+
+    // #then - agents should still be created using fallback chain
+    expect(agents.oracle).toBeDefined()
+    expect(agents.oracle.model).toBe("openai/gpt-5.2")
+  })
+
+  test("sisyphus uses fallback chain when systemDefaultModel undefined", async () => {
+    // #given - no systemDefaultModel
+
+    // #when
+    const agents = await createBuiltinAgents([], {}, undefined, undefined)
+
+    // #then - sisyphus should use its fallback chain
+    expect(agents.sisyphus).toBeDefined()
+    expect(agents.sisyphus.model).toBe("anthropic/claude-opus-4-5")
+  })
+})
+
 describe("buildAgent with category and skills", () => {
   const { buildAgent } = require("./utils")
   const TEST_MODEL = "anthropic/claude-opus-4-5"

src/agents/utils.ts

@@ -151,10 +151,6 @@ export async function createBuiltinAgents(
   client?: any,
   browserProvider?: BrowserAutomationProvider
 ): Promise<Record<string, AgentConfig>> {
-  if (!systemDefaultModel) {
-    throw new Error("createBuiltinAgents requires systemDefaultModel")
-  }
-
   const connectedProviders = readConnectedProvidersCache()
   const availableModels = client 
     ? await fetchAvailableModels(client, { connectedProviders: connectedProviders ?? undefined }) 
@@ -201,13 +197,14 @@ export async function createBuiltinAgents(
     const override = findCaseInsensitive(agentOverrides, agentName)
     const requirement = AGENT_MODEL_REQUIREMENTS[agentName]
 
-    // Use resolver to determine model
-    const { model, variant: resolvedVariant } = resolveModelWithFallback({
+    const resolution = resolveModelWithFallback({
       userModel: override?.model,
       fallbackChain: requirement?.fallbackChain,
       availableModels,
       systemDefaultModel,
     })
+    if (!resolution) continue
+    const { model, variant: resolvedVariant } = resolution
 
     let config = buildAgent(source, model, mergedCategories, gitMasterConfig, browserProvider)
 
@@ -243,72 +240,76 @@ export async function createBuiltinAgents(
      const sisyphusOverride = agentOverrides["sisyphus"]
      const sisyphusRequirement = AGENT_MODEL_REQUIREMENTS["sisyphus"]
 
-    // Use resolver to determine model
-    const { model: sisyphusModel, variant: sisyphusResolvedVariant } = resolveModelWithFallback({
+    const sisyphusResolution = resolveModelWithFallback({
       userModel: sisyphusOverride?.model,
       fallbackChain: sisyphusRequirement?.fallbackChain,
       availableModels,
       systemDefaultModel,
     })
 
-    let sisyphusConfig = createSisyphusAgent(
-      sisyphusModel,
-      availableAgents,
-      undefined,
-      availableSkills,
-      availableCategories
-    )
-
-    // Apply variant from override or resolved fallback chain
-    if (sisyphusOverride?.variant) {
-      sisyphusConfig = { ...sisyphusConfig, variant: sisyphusOverride.variant }
-    } else if (sisyphusResolvedVariant) {
-      sisyphusConfig = { ...sisyphusConfig, variant: sisyphusResolvedVariant }
-    }
+    if (sisyphusResolution) {
+      const { model: sisyphusModel, variant: sisyphusResolvedVariant } = sisyphusResolution
+
+      let sisyphusConfig = createSisyphusAgent(
+        sisyphusModel,
+        availableAgents,
+        undefined,
+        availableSkills,
+        availableCategories
+      )
+
+      if (sisyphusOverride?.variant) {
+        sisyphusConfig = { ...sisyphusConfig, variant: sisyphusOverride.variant }
+      } else if (sisyphusResolvedVariant) {
+        sisyphusConfig = { ...sisyphusConfig, variant: sisyphusResolvedVariant }
+      }
 
-    if (directory && sisyphusConfig.prompt) {
-      const envContext = createEnvContext()
-      sisyphusConfig = { ...sisyphusConfig, prompt: sisyphusConfig.prompt + envContext }
-    }
+      if (directory && sisyphusConfig.prompt) {
+        const envContext = createEnvContext()
+        sisyphusConfig = { ...sisyphusConfig, prompt: sisyphusConfig.prompt + envContext }
+      }
 
-    if (sisyphusOverride) {
-      sisyphusConfig = mergeAgentConfig(sisyphusConfig, sisyphusOverride)
-    }
+      if (sisyphusOverride) {
+        sisyphusConfig = mergeAgentConfig(sisyphusConfig, sisyphusOverride)
+      }
 
-     result["sisyphus"] = sisyphusConfig
+      result["sisyphus"] = sisyphusConfig
+    }
    }
 
    if (!disabledAgents.includes("atlas")) {
      const orchestratorOverride = agentOverrides["atlas"]
      const atlasRequirement = AGENT_MODEL_REQUIREMENTS["atlas"]
 
-    // Use resolver to determine model
-    const { model: atlasModel, variant: atlasResolvedVariant } = resolveModelWithFallback({
+    const atlasResolution = resolveModelWithFallback({
       userModel: orchestratorOverride?.model,
       fallbackChain: atlasRequirement?.fallbackChain,
       availableModels,
       systemDefaultModel,
     })
 
-    let orchestratorConfig = createAtlasAgent({
-      model: atlasModel,
-      availableAgents,
-      availableSkills,
-      userCategories: categories,
-    })
-
-    // Apply variant from override or resolved fallback chain
-    if (orchestratorOverride?.variant) {
-      orchestratorConfig = { ...orchestratorConfig, variant: orchestratorOverride.variant }
-    } else if (atlasResolvedVariant) {
-      orchestratorConfig = { ...orchestratorConfig, variant: atlasResolvedVariant }
-    }
+    if (atlasResolution) {
+      const { model: atlasModel, variant: atlasResolvedVariant } = atlasResolution
+
+      let orchestratorConfig = createAtlasAgent({
+        model: atlasModel,
+        availableAgents,
+        availableSkills,
+        userCategories: categories,
+      })
+
+      if (orchestratorOverride?.variant) {
+        orchestratorConfig = { ...orchestratorConfig, variant: orchestratorOverride.variant }
+      } else if (atlasResolvedVariant) {
+        orchestratorConfig = { ...orchestratorConfig, variant: atlasResolvedVariant }
+      }
 
-    if (orchestratorOverride) {
-      orchestratorConfig = mergeAgentConfig(orchestratorConfig, orchestratorOverride)
-    }
+      if (orchestratorOverride) {
+        orchestratorConfig = mergeAgentConfig(orchestratorConfig, orchestratorOverride)
+      }
 
-     result["atlas"] = orchestratorConfig
+      result["atlas"] = orchestratorConfig
+    }
    }
 
    return result

src/plugin-handlers/config-handler.ts

@@ -105,41 +105,6 @@ export function createConfigHandler(deps: ConfigHandlerDeps) {
       log(`Plugin load errors`, { errors: pluginComponents.errors });
     }
 
-    if (!(config.model as string | undefined)?.trim()) {
-      let fallbackModel: string | undefined
-
-      for (const agentConfig of Object.values(pluginConfig.agents ?? {})) {
-        const model = (agentConfig as { model?: string })?.model
-        if (model && typeof model === 'string' && model.trim()) {
-          fallbackModel = model.trim()
-          break
-        }
-      }
-
-      if (!fallbackModel) {
-        for (const categoryConfig of Object.values(pluginConfig.categories ?? {})) {
-          const model = (categoryConfig as { model?: string })?.model
-          if (model && typeof model === 'string' && model.trim()) {
-            fallbackModel = model.trim()
-            break
-          }
-        }
-      }
-
-      if (fallbackModel) {
-        config.model = fallbackModel
-        log(`No default model specified, using fallback from config: ${fallbackModel}`)
-      } else {
-        const paths = getOpenCodeConfigPaths({ binary: "opencode", version: null })
-        throw new Error(
-          'oh-my-opencode requires a default model.\n\n' +
-          `Add this to ${paths.configJsonc}:\n\n` +
-          '  "model": "anthropic/claude-sonnet-4-5"\n\n' +
-          '(Replace with your preferred provider/model)'
-        )
-      }
-    }
-
     // Migrate disabled_agents from old names to new names
     const migratedDisabledAgents = (pluginConfig.disabled_agents ?? []).map(agent => {
       return AGENT_NAME_MAP[agent.toLowerCase()] ?? AGENT_NAME_MAP[agent] ?? agent