fix: remove github-copilot from gpt-5.3-codex provider list

gpt-5.3-codex is not available on GitHub Copilot. The fallback chains
incorrectly listed github-copilot as a valid provider for this model,
causing the doctor to report 'configured model github-copilot/gpt-5.3-codex
is not valid' for Hephaestus agent.

Affected agents: hephaestus (requiresProvider + fallbackChain)
Affected categories: ultrabrain, deep, unspecified-low

Copilot users can still use Hephaestus via openai or opencode providers.

Fixes #2047

src/cli/__snapshots__/model-fallback.test.ts.snap

@@ -750,10 +750,6 @@ exports[`generateModelConfig fallback providers uses GitHub Copilot models when
     "explore": {
       "model": "github-copilot/gpt-5-mini",
     },
-    "hephaestus": {
-      "model": "github-copilot/gpt-5.3-codex",
-      "variant": "medium",
-    },
     "librarian": {
       "model": "github-copilot/claude-sonnet-4.5",
     },
@@ -786,16 +782,12 @@ exports[`generateModelConfig fallback providers uses GitHub Copilot models when
       "model": "github-copilot/gemini-3-pro-preview",
       "variant": "high",
     },
-    "deep": {
-      "model": "github-copilot/gpt-5.3-codex",
-      "variant": "medium",
-    },
     "quick": {
       "model": "github-copilot/claude-haiku-4.5",
     },
     "ultrabrain": {
-      "model": "github-copilot/gpt-5.3-codex",
-      "variant": "xhigh",
+      "model": "github-copilot/gemini-3-pro-preview",
+      "variant": "high",
     },
     "unspecified-high": {
       "model": "github-copilot/claude-sonnet-4.5",
@@ -824,10 +816,6 @@ exports[`generateModelConfig fallback providers uses GitHub Copilot models with
     "explore": {
       "model": "github-copilot/gpt-5-mini",
     },
-    "hephaestus": {
-      "model": "github-copilot/gpt-5.3-codex",
-      "variant": "medium",
-    },
     "librarian": {
       "model": "github-copilot/claude-sonnet-4.5",
     },
@@ -860,16 +848,12 @@ exports[`generateModelConfig fallback providers uses GitHub Copilot models with
       "model": "github-copilot/gemini-3-pro-preview",
       "variant": "high",
     },
-    "deep": {
-      "model": "github-copilot/gpt-5.3-codex",
-      "variant": "medium",
-    },
     "quick": {
       "model": "github-copilot/claude-haiku-4.5",
     },
     "ultrabrain": {
-      "model": "github-copilot/gpt-5.3-codex",
-      "variant": "xhigh",
+      "model": "github-copilot/gemini-3-pro-preview",
+      "variant": "high",
     },
     "unspecified-high": {
       "model": "github-copilot/claude-opus-4.6",
@@ -1285,7 +1269,7 @@ exports[`generateModelConfig mixed provider scenarios uses all fallback provider
       "model": "opencode/claude-haiku-4-5",
     },
     "hephaestus": {
-      "model": "github-copilot/gpt-5.3-codex",
+      "model": "opencode/gpt-5.3-codex",
       "variant": "medium",
     },
     "librarian": {
@@ -1321,14 +1305,14 @@ exports[`generateModelConfig mixed provider scenarios uses all fallback provider
       "variant": "high",
     },
     "deep": {
-      "model": "github-copilot/gpt-5.3-codex",
+      "model": "opencode/gpt-5.3-codex",
       "variant": "medium",
     },
     "quick": {
       "model": "github-copilot/claude-haiku-4.5",
     },
     "ultrabrain": {
-      "model": "github-copilot/gpt-5.3-codex",
+      "model": "opencode/gpt-5.3-codex",
       "variant": "xhigh",
     },
     "unspecified-high": {

src/cli/model-fallback-requirements.ts

@@ -17,9 +17,9 @@ export const CLI_AGENT_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
   },
   hephaestus: {
     fallbackChain: [
-      { providers: ["openai", "github-copilot", "opencode"], model: "gpt-5.3-codex", variant: "medium" },
+      { providers: ["openai", "opencode"], model: "gpt-5.3-codex", variant: "medium" },
     ],
-    requiresProvider: ["openai", "github-copilot", "opencode"],
+    requiresProvider: ["openai", "opencode"],
   },
   oracle: {
     fallbackChain: [
@@ -100,14 +100,14 @@ export const CLI_CATEGORY_MODEL_REQUIREMENTS: Record<string, ModelRequirement> =
   },
   ultrabrain: {
     fallbackChain: [
-      { providers: ["openai", "github-copilot", "opencode"], model: "gpt-5.3-codex", variant: "xhigh" },
+      { providers: ["openai", "opencode"], model: "gpt-5.3-codex", variant: "xhigh" },
       { providers: ["google", "github-copilot", "opencode"], model: "gemini-3-pro", variant: "high" },
       { providers: ["anthropic", "github-copilot", "opencode"], model: "claude-opus-4-6", variant: "max" },
     ],
   },
   deep: {
     fallbackChain: [
-      { providers: ["openai", "github-copilot", "opencode"], model: "gpt-5.3-codex", variant: "medium" },
+      { providers: ["openai", "opencode"], model: "gpt-5.3-codex", variant: "medium" },
       { providers: ["anthropic", "github-copilot", "opencode"], model: "claude-opus-4-6", variant: "max" },
       { providers: ["google", "github-copilot", "opencode"], model: "gemini-3-pro", variant: "high" },
     ],
@@ -131,7 +131,7 @@ export const CLI_CATEGORY_MODEL_REQUIREMENTS: Record<string, ModelRequirement> =
   "unspecified-low": {
     fallbackChain: [
       { providers: ["anthropic", "github-copilot", "opencode"], model: "claude-sonnet-4-5" },
-      { providers: ["openai", "github-copilot", "opencode"], model: "gpt-5.3-codex", variant: "medium" },
+      { providers: ["openai", "opencode"], model: "gpt-5.3-codex", variant: "medium" },
       { providers: ["google", "github-copilot", "opencode"], model: "gemini-3-flash" },
     ],
   },

src/cli/model-fallback.test.ts

@@ -421,16 +421,15 @@ describe("generateModelConfig", () => {
       expect(result.agents?.hephaestus?.variant).toBe("medium")
     })
 
-    test("Hephaestus is created when Copilot is available (github-copilot provider connected)", () => {
+    test("Hephaestus is NOT created when only Copilot is available (gpt-5.3-codex unavailable on github-copilot)", () => {
       // #given
       const config = createConfig({ hasCopilot: true })
 
       // #when
       const result = generateModelConfig(config)
 
-      // #then
-      expect(result.agents?.hephaestus?.model).toBe("github-copilot/gpt-5.3-codex")
-      expect(result.agents?.hephaestus?.variant).toBe("medium")
+      // #then - hephaestus is omitted because gpt-5.3-codex is not available on github-copilot
+      expect(result.agents?.hephaestus).toBeUndefined()
     })
 
     test("Hephaestus is created when OpenCode Zen is available (opencode provider connected)", () => {