refactor(pkg-r): remove dead else branch in mod_server

[cpsievert]

Summary

Removes an unreachable else branch in mod_server() that was left behind after #207 refactored client creation.

Before #207, mod_server() accepted either a function (client factory) or a pre-built Chat object. The else branch handled the latter case by cloning the Chat and manually registering tools.

After #207, QueryChat$server() always wraps private$create_session_client() in a closure and passes that as client — so mod_server() always receives a function. The else branch became dead code.

This is a problem because the else branch:

• Hardcodes registering only update, query, and reset tools (ignoring the tools parameter)
• Would silently do the wrong thing if somehow reached

This PR replaces the if/else with check_function(client) + a direct call, matching the Python mod_server which raises TypeError for non-callable clients.

Test plan

• Existing test suite passes (622 tests, 0 failures)
• Verified via git log that no code path passes a non-function client to mod_server() since feat: Allow deferred chat client initialization #207

[Copilot]

Pull request overview

Removes unreachable logic in the R Shiny module server (mod_server()) by enforcing that client must be a function (consistent with the post-#207 architecture where QueryChat$server() always passes a closure that creates a session-scoped chat client).

Changes:

• Replace if (is_function(client)) ... else ... with check_function(client) and a direct invocation.
• Eliminate dead code that cloned a Chat instance and manually registered a fixed subset of tools.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.