feat: check provider connectivity instead of specific model for hephaestus availability

Hephaestus now appears when any of its providers (openai, github-copilot, opencode) is
connected, rather than requiring the exact gpt-5.2-codex model. This allows users with
newer codex models (e.g., gpt-5.3-codex) to use Hephaestus without manual config overrides.

- Add requiresProvider field to ModelRequirement type
- Add isAnyProviderConnected() helper in model-availability
- Update hephaestus config from requiresModel to requiresProvider
- Update cli model-fallback to handle requiresProvider checks

src/agents/utils.test.ts

@@ -240,13 +240,13 @@ describe("createBuiltinAgents without systemDefaultModel", () => {
   })
 })
 
-describe("createBuiltinAgents with requiresModel gating", () => {
-  test("hephaestus is not created when gpt-5.2-codex is unavailable and provider not connected", async () => {
-    // #given
+describe("createBuiltinAgents with requiresProvider gating (hephaestus)", () => {
+  test("hephaestus is not created when no required provider is connected", async () => {
+    // #given - only anthropic models available, not in hephaestus requiresProvider
     const fetchSpy = spyOn(shared, "fetchAvailableModels").mockResolvedValue(
       new Set(["anthropic/claude-opus-4-5"])
     )
-    const cacheSpy = spyOn(connectedProvidersCache, "readConnectedProvidersCache").mockReturnValue([])
+    const cacheSpy = spyOn(connectedProvidersCache, "readConnectedProvidersCache").mockReturnValue(["anthropic"])
 
     try {
       // #when
@@ -260,8 +260,8 @@ describe("createBuiltinAgents with requiresModel gating", () => {
     }
   })
 
-  test("hephaestus is created when gpt-5.2-codex is available", async () => {
-    // #given
+  test("hephaestus is created when openai provider is connected", async () => {
+    // #given - openai provider has models available
     const fetchSpy = spyOn(shared, "fetchAvailableModels").mockResolvedValue(
       new Set(["openai/gpt-5.2-codex"])
     )
@@ -277,6 +277,40 @@ describe("createBuiltinAgents with requiresModel gating", () => {
     }
   })
 
+  test("hephaestus is created when github-copilot provider is connected", async () => {
+    // #given - github-copilot provider has models available
+    const fetchSpy = spyOn(shared, "fetchAvailableModels").mockResolvedValue(
+      new Set(["github-copilot/gpt-5.2-codex"])
+    )
+
+    try {
+      // #when
+      const agents = await createBuiltinAgents([], {}, undefined, TEST_DEFAULT_MODEL, undefined, undefined, [], {})
+
+      // #then
+      expect(agents.hephaestus).toBeDefined()
+    } finally {
+      fetchSpy.mockRestore()
+    }
+  })
+
+  test("hephaestus is created when opencode provider is connected", async () => {
+    // #given - opencode provider has models available
+    const fetchSpy = spyOn(shared, "fetchAvailableModels").mockResolvedValue(
+      new Set(["opencode/gpt-5.2-codex"])
+    )
+
+    try {
+      // #when
+      const agents = await createBuiltinAgents([], {}, undefined, TEST_DEFAULT_MODEL, undefined, undefined, [], {})
+
+      // #then
+      expect(agents.hephaestus).toBeDefined()
+    } finally {
+      fetchSpy.mockRestore()
+    }
+  })
+
   test("hephaestus is created on first run when no availableModels or cache exist", async () => {
     // #given
     const cacheSpy = spyOn(connectedProvidersCache, "readConnectedProvidersCache").mockReturnValue(null)
@@ -295,7 +329,7 @@ describe("createBuiltinAgents with requiresModel gating", () => {
     }
   })
 
-  test("hephaestus is created when explicit config provided even if model unavailable", async () => {
+  test("hephaestus is created when explicit config provided even if provider unavailable", async () => {
     // #given
     const fetchSpy = spyOn(shared, "fetchAvailableModels").mockResolvedValue(
       new Set(["anthropic/claude-opus-4-5"])