After the main agent moved to its own build_main_agent_tools, nothing calls
the shared registry's builders. Delete the dead functions (build_tools,
build_tools_async, get_tool_by_name, get_all_tool_names,
get_default_enabled_tools) plus the now-orphaned load_mcp_tools import and the
stale __init__ re-exports.
BUILTIN_TOOLS, ToolDefinition, and get_connector_gated_tools are retained:
the catalog is still consumed for tool *metadata* (action_log revert/dedup
resolvers and the /agent/tools listing). Also drop stale references to the
deleted chat_deepagent.py within the agents module.
Verified: full unit suite green (2431 passed, 1 skipped); lints clean.
Three live shared leaves discovered while taking stock after slice 7 (all are
consumed by the multi-agent stack and/or live routes, not single-agent-only):
- connector_searchable_types -> shared + shim (multi-agent factory uses it)
- agent_cache -> shared + shim (multi-agent runtime/agent_cache uses it)
- system_prompt + prompts/ (42 .md fragments) -> shared together + shim.
Repointed composer's _PROMPTS_PACKAGE to app.agents.shared.prompts so
importlib.resources fragment loading keeps working; system_prompt's relative
".prompts.composer" import is preserved by moving both as a unit.
Each keeps a re-export shim for the frozen chat_deepagent. After this slice,
new_chat/ holds only the frozen single-agent stack (chat_deepagent, subagents/,
__init__) plus shims.
