feat: make gpt-5.3-codex medium the primary model for multimodal-looker

GPT-5.3 Codex has strong multimodal capabilities. Promote it to first
candidate in multimodal-looker fallback chain, with gemini-3-flash
following (matching the ULW pattern of gpt-5.3-codex -> gemini).

src/cli/model-fallback-requirements.ts

@@ -44,6 +44,7 @@ export const CLI_AGENT_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
   },
   "multimodal-looker": {
     fallbackChain: [
+      { providers: ["openai", "opencode"], model: "gpt-5.3-codex", variant: "medium" },
       { providers: ["google", "github-copilot", "opencode"], model: "gemini-3-flash" },
       { providers: ["openai", "github-copilot", "opencode"], model: "gpt-5.2" },
       { providers: ["zai-coding-plan"], model: "glm-4.6v" },

src/shared/model-requirements.test.ts

@@ -86,21 +86,25 @@ describe("AGENT_MODEL_REQUIREMENTS", () => {
     expect(quaternary.model).toBe("gpt-5-nano")
   })
 
-  test("multimodal-looker has valid fallbackChain with kimi-k2.5-free as primary", () => {
+  test("multimodal-looker has valid fallbackChain with gpt-5.3-codex as primary", () => {
     // given - multimodal-looker agent requirement
     const multimodalLooker = AGENT_MODEL_REQUIREMENTS["multimodal-looker"]
 
     // when - accessing multimodal-looker requirement
-    // then - fallbackChain exists with kimi-k2.5-free first, gpt-5-nano last
+    // then - fallbackChain exists with gpt-5.3-codex first, gemini-3-flash second, gpt-5-nano last
     expect(multimodalLooker).toBeDefined()
     expect(multimodalLooker.fallbackChain).toBeArray()
-    expect(multimodalLooker.fallbackChain).toHaveLength(5)
+    expect(multimodalLooker.fallbackChain).toHaveLength(6)
 
     const primary = multimodalLooker.fallbackChain[0]
-    expect(primary.providers[0]).toBe("opencode")
-    expect(primary.model).toBe("kimi-k2.5-free")
+    expect(primary.providers).toEqual(["openai", "opencode"])
+    expect(primary.model).toBe("gpt-5.3-codex")
+    expect(primary.variant).toBe("medium")
 
-    const last = multimodalLooker.fallbackChain[4]
+    const secondary = multimodalLooker.fallbackChain[1]
+    expect(secondary.model).toBe("gemini-3-flash")
+
+    const last = multimodalLooker.fallbackChain[5]
     expect(last.providers).toEqual(["openai", "github-copilot", "opencode"])
     expect(last.model).toBe("gpt-5-nano")
   })

src/shared/model-requirements.ts

@@ -53,8 +53,9 @@ export const AGENT_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
   },
   "multimodal-looker": {
     fallbackChain: [
-      { providers: ["opencode"], model: "kimi-k2.5-free" },
+      { providers: ["openai", "opencode"], model: "gpt-5.3-codex", variant: "medium" },
       { providers: ["google", "github-copilot", "opencode"], model: "gemini-3-flash" },
+      { providers: ["opencode"], model: "kimi-k2.5-free" },
       { providers: ["openai", "github-copilot", "opencode"], model: "gpt-5.2" },
       { providers: ["zai-coding-plan"], model: "glm-4.6v" },
       { providers: ["openai", "github-copilot", "opencode"], model: "gpt-5-nano" },