fix(model-requirements): align fallback models with available provider catalogs

- opencode/minimax-m2.7-highspeed → opencode/minimax-m2.5 (provider lacks m2.7 variants)
- opencode-go/minimax-m2.7-highspeed → opencode-go/minimax-m2.7 (provider lacks -highspeed)
- opencode/minimax-m2.7 → opencode/minimax-m2.5 (provider only has m2.5)
- added xai as alternative provider for grok-code-fast-1 (prevents wrong provider prefix)

src/shared/model-requirements.test.ts

@@ -80,7 +80,7 @@ describe("AGENT_MODEL_REQUIREMENTS", () => {
 
     const second = librarian.fallbackChain[1]
     expect(second.providers[0]).toBe("opencode")
-    expect(second.model).toBe("minimax-m2.7-highspeed")
+    expect(second.model).toBe("minimax-m2.5")
 
     const tertiary = librarian.fallbackChain[2]
     expect(tertiary.providers).toContain("anthropic")
@@ -95,22 +95,22 @@ describe("AGENT_MODEL_REQUIREMENTS", () => {
     const explore = AGENT_MODEL_REQUIREMENTS["explore"]
 
     // when - accessing explore requirement
-    // then - fallbackChain: grok → minimax-m2.7-highspeed → minimax-m2.7 → haiku → nano
     expect(explore).toBeDefined()
     expect(explore.fallbackChain).toBeArray()
     expect(explore.fallbackChain).toHaveLength(5)
 
     const primary = explore.fallbackChain[0]
     expect(primary.providers).toContain("github-copilot")
+    expect(primary.providers).toContain("xai")
     expect(primary.model).toBe("grok-code-fast-1")
 
     const secondary = explore.fallbackChain[1]
     expect(secondary.providers).toContain("opencode-go")
-    expect(secondary.model).toBe("minimax-m2.7-highspeed")
+    expect(secondary.model).toBe("minimax-m2.7")
 
     const tertiary = explore.fallbackChain[2]
     expect(tertiary.providers).toContain("opencode")
-    expect(tertiary.model).toBe("minimax-m2.7")
+    expect(tertiary.model).toBe("minimax-m2.5")
 
     const quaternary = explore.fallbackChain[3]
     expect(quaternary.providers).toContain("anthropic")

src/shared/model-requirements.ts

@@ -78,16 +78,16 @@ export const AGENT_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
   librarian: {
     fallbackChain: [
       { providers: ["opencode-go"], model: "minimax-m2.7" },
-      { providers: ["opencode"], model: "minimax-m2.7-highspeed" },
+      { providers: ["opencode"], model: "minimax-m2.5" },
       { providers: ["anthropic", "opencode"], model: "claude-haiku-4-5" },
       { providers: ["opencode"], model: "gpt-5-nano" },
     ],
   },
   explore: {
     fallbackChain: [
-      { providers: ["github-copilot"], model: "grok-code-fast-1" },
-      { providers: ["opencode-go"], model: "minimax-m2.7-highspeed" },
-      { providers: ["opencode"], model: "minimax-m2.7" },
+      { providers: ["github-copilot", "xai"], model: "grok-code-fast-1" },
+      { providers: ["opencode-go"], model: "minimax-m2.7" },
+      { providers: ["opencode"], model: "minimax-m2.5" },
       { providers: ["anthropic", "opencode"], model: "claude-haiku-4-5" },
       { providers: ["opencode"], model: "gpt-5-nano" },
     ],