ROADMAP-17 — P2 — Dead code removal and default centralization #109

Series: ROADMAP — filed from the 2026-10-27 whole-project assessment · Backlog task: M16-T04 · Priority: P2 · Effort: small

Problem

A removal sweep found pure dead weight:

1. @tool decorator wraps every tool to attach __tool_entry__ / __tool_schema__ — never read anywhere (grep across agentkit/, tests/, examples/)
2. default_registry module-level singleton — violates the project's "no global state" rule and nothing queries it (only its own definition and the decorator fallback)
3. db/session.get_session() — defined, never imported
4. routes.py router = runs_router # backwards compat alias — its target imports it under the same name; compatibility protects nothing
5. Model-name defaults duplicated: gemini-3.1-flash-lite ×3 (factory.py:41, gemini.py:45, config.py:208), gpt-4o ×2
6. Error subclasses with no raise site: ToolValidationError, ToolExecutionError, ToolTimeoutError, ToolNotFound(alias) — the executor deliberately returns ToolResult.failure instead of raising

Evidence

• agentkit/tools/registry.py:107,139,144–155
• agentkit/db/session.py:26–31; agentkit/api/routes.py:44
• agentkit/core/errors.py:80,91,102,113 vs agentkit/api/main.py:25

Suggested fix / acceptance criteria

• Decide and document writer-vs-reader for the tool attributes: either use them or delete the wrapper machinery (plain register + return fn)
• Remove default_registry (or keep with an explicit deprecation note + consumer), remove get_session, the alias
• Single source of truth for model-name defaults
• Dead error subclasses deleted unless mapped in api/main.py handlers — list what was kept and why
• tests/unit/test_tool_registry.py and friends updated; suite green

Suggested branch / commit

chore/remove-dead-code · chore: delete dead code and centralize default constants