fix: respect user-configured agent models over system defaults

When user explicitly configures an agent model in oh-my-opencode.json,
that model should take priority over the active model in OpenCode's config
(which may just be the system default, not a deliberate UI selection).

This fixes the issue where user-configured models from plugin providers
(e.g., google/antigravity-*) were being overridden by the fallback chain
because config.model was being passed as uiSelectedModel regardless of
whether the user had an explicit config.

The fix:
- Only pass uiSelectedModel when there's no explicit userModel config
- If user has configured a model, let resolveModelPipeline use it directly

Fixes #1573

src/agents/utils.test.ts

@@ -79,6 +79,72 @@ describe("createBuiltinAgents with model overrides", () => {
     }
   })
 
+  test("user config model takes priority over uiSelectedModel for sisyphus", async () => {
+    // #given
+    const fetchSpy = spyOn(shared, "fetchAvailableModels").mockResolvedValue(
+      new Set(["openai/gpt-5.2", "anthropic/claude-sonnet-4-5"])
+    )
+    const uiSelectedModel = "openai/gpt-5.2"
+    const overrides = {
+      sisyphus: { model: "google/antigravity-claude-opus-4-5-thinking" },
+    }
+
+    try {
+      // #when
+      const agents = await createBuiltinAgents(
+        [],
+        overrides,
+        undefined,
+        TEST_DEFAULT_MODEL,
+        undefined,
+        undefined,
+        [],
+        undefined,
+        undefined,
+        uiSelectedModel
+      )
+
+      // #then
+      expect(agents.sisyphus).toBeDefined()
+      expect(agents.sisyphus.model).toBe("google/antigravity-claude-opus-4-5-thinking")
+    } finally {
+      fetchSpy.mockRestore()
+    }
+  })
+
+  test("user config model takes priority over uiSelectedModel for atlas", async () => {
+    // #given
+    const fetchSpy = spyOn(shared, "fetchAvailableModels").mockResolvedValue(
+      new Set(["openai/gpt-5.2", "anthropic/claude-sonnet-4-5"])
+    )
+    const uiSelectedModel = "openai/gpt-5.2"
+    const overrides = {
+      atlas: { model: "google/antigravity-claude-opus-4-5-thinking" },
+    }
+
+    try {
+      // #when
+      const agents = await createBuiltinAgents(
+        [],
+        overrides,
+        undefined,
+        TEST_DEFAULT_MODEL,
+        undefined,
+        undefined,
+        [],
+        undefined,
+        undefined,
+        uiSelectedModel
+      )
+
+      // #then
+      expect(agents.atlas).toBeDefined()
+      expect(agents.atlas.model).toBe("google/antigravity-claude-opus-4-5-thinking")
+    } finally {
+      fetchSpy.mockRestore()
+    }
+  })
+
   test("Sisyphus is created on first run when no availableModels or cache exist", async () => {
     // #given
     const systemDefaultModel = "anthropic/claude-opus-4-6"
@@ -422,6 +488,58 @@ describe("createBuiltinAgents with requiresAnyModel gating (sisyphus)", () => {
       cacheSpy.mockRestore()
     }
   })
+
+  test("sisyphus uses user-configured plugin model even when not in cache or fallback chain", async () => {
+    // #given - user configures a model from a plugin provider (like antigravity)
+    // that is NOT in the availableModels cache and NOT in the fallback chain
+    const fetchSpy = spyOn(shared, "fetchAvailableModels").mockResolvedValue(
+      new Set(["openai/gpt-5.2"])
+    )
+    const cacheSpy = spyOn(connectedProvidersCache, "readConnectedProvidersCache").mockReturnValue(
+      ["openai"]
+    )
+    const overrides = {
+      sisyphus: { model: "google/antigravity-claude-opus-4-5-thinking" },
+    }
+
+    try {
+      // #when
+      const agents = await createBuiltinAgents([], overrides, undefined, TEST_DEFAULT_MODEL, undefined, undefined, [], {})
+
+      // #then
+      expect(agents.sisyphus).toBeDefined()
+      expect(agents.sisyphus.model).toBe("google/antigravity-claude-opus-4-5-thinking")
+    } finally {
+      fetchSpy.mockRestore()
+      cacheSpy.mockRestore()
+    }
+  })
+
+  test("sisyphus uses user-configured plugin model when availableModels is empty but cache exists", async () => {
+    // #given - connected providers cache exists but models cache is empty
+    // This reproduces the exact scenario where provider-models.json has models: {}
+    const fetchSpy = spyOn(shared, "fetchAvailableModels").mockResolvedValue(
+      new Set()
+    )
+    const cacheSpy = spyOn(connectedProvidersCache, "readConnectedProvidersCache").mockReturnValue(
+      ["google", "openai", "opencode"]
+    )
+    const overrides = {
+      sisyphus: { model: "google/antigravity-claude-opus-4-5-thinking" },
+    }
+
+    try {
+      // #when
+      const agents = await createBuiltinAgents([], overrides, undefined, TEST_DEFAULT_MODEL, undefined, undefined, [], {})
+
+      // #then
+      expect(agents.sisyphus).toBeDefined()
+      expect(agents.sisyphus.model).toBe("google/antigravity-claude-opus-4-5-thinking")
+    } finally {
+      fetchSpy.mockRestore()
+      cacheSpy.mockRestore()
+    }
+  })
 })
 
 describe("buildAgent with category and skills", () => {

src/agents/utils.ts

@@ -304,7 +304,7 @@ export async function createBuiltinAgents(
      const isPrimaryAgent = isFactory(source) && source.mode === "primary"
 
     const resolution = applyModelResolution({
-      uiSelectedModel: isPrimaryAgent ? uiSelectedModel : undefined,
+      uiSelectedModel: (isPrimaryAgent && !override?.model) ? uiSelectedModel : undefined,
       userModel: override?.model,
       requirement,
       availableModels,
@@ -356,7 +356,7 @@ export async function createBuiltinAgents(
 
    if (!disabledAgents.includes("sisyphus") && meetsSisyphusAnyModelRequirement) {
     let sisyphusResolution = applyModelResolution({
-      uiSelectedModel,
+      uiSelectedModel: sisyphusOverride?.model ? undefined : uiSelectedModel,
       userModel: sisyphusOverride?.model,
       requirement: sisyphusRequirement,
       availableModels,
@@ -454,7 +454,7 @@ export async function createBuiltinAgents(
       const atlasRequirement = AGENT_MODEL_REQUIREMENTS["atlas"]
 
       const atlasResolution = applyModelResolution({
-        uiSelectedModel,
+        uiSelectedModel: orchestratorOverride?.model ? undefined : uiSelectedModel,
         userModel: orchestratorOverride?.model,
         requirement: atlasRequirement,
         availableModels,