fix(athena): remove athena primary from delegation list and switch_agent targets

Athena primary should not be routable via switch_agent or appear in the
delegation table. Only athena-junior (subagent) remains delegatable via task().

- Remove athena from ALLOWED_AGENTS and DESCRIPTION in switch-agent tool
- Remove ATHENA_PROMPT_METADATA from agentMetadata, agent.ts, barrel export
- Update switch-agent test to assert athena rejection
- Remove ATHENA_PROMPT_METADATA test block

src/tools/switch-agent/tools.test.ts

@@ -188,21 +188,19 @@ describe("switch_agent tool", () => {
     expect(promptedSessions[0]!.path.id).toBe("direct-id-123")
   })
 
-  //#given valid athena switch args
+  //#given athena switch args (athena is not a valid switch target)
   //#when execute is called
-  //#then it creates a new session and prompts with the athena agent
-  test("should create session and prompt for athena switch", async () => {
+  //#then it rejects the switch since athena primary is not in ALLOWED_AGENTS
+  test("should reject athena as switch target", async () => {
     const tool = createToolWithMockClient()
     const result = await tool.execute(
       { agent: "athena", context: "Run council analysis on the architecture decision" },
       toolContext
     )
 
+    expect(result).toContain("Invalid switch target")
     expect(result).toContain("athena")
-    expect(result).toContain("new-session-abc")
-    expect(createdSessions).toHaveLength(1)
-    expect(promptedSessions).toHaveLength(1)
-    expect(promptedSessions[0]!.path.id).toBe("new-session-abc")
-    expect(promptedSessions[0]!.body.parts[0]!.text).toBe("Run council analysis on the architecture decision")
+    expect(createdSessions).toHaveLength(0)
+    expect(promptedSessions).toHaveLength(0)
   })
 })

src/tools/switch-agent/tools.ts

@@ -8,9 +8,9 @@ const DESCRIPTION =
   "with the provided context as its starting prompt. Use this to route work to another agent " +
   "(e.g., Atlas for fixes, Prometheus for planning). The switch executes when the current agent's turn completes.\n\n" +
   "Permanent one-way handoff. Use ONLY when you're the wrong agent for the overall job, NEVER for subtasks (use task()). " +
-  "Targets: atlas, prometheus, sisyphus, hephaestus, athena (multi-model council)."
+  "Targets: atlas, prometheus, sisyphus, hephaestus."
 
-const ALLOWED_AGENTS = new Set(["atlas", "prometheus", "sisyphus", "hephaestus", "athena"])
+const ALLOWED_AGENTS = new Set(["atlas", "prometheus", "sisyphus", "hephaestus"])
 
 type SessionClient = {
   session: {