feat: drop self-hosted mcp servers and tool labels overwrite

[galuszkm]

Description

Two related refactors that shrink the public surface and fix behaviour that was silently wrong.
Net: ~1.5k lines removed.

1. Drop self-hosted MCP servers, collapse resolution into load()

strands-compose acted as both an MCP client and an MCP server host.
Hosting was a second responsibility that duplicated what the MCP SDK already does, so mcp_servers:, MCPServerDef, server: on clients, create_mcp_server, and MCPLifecycle are gone.
We now support only stdio (client spawns the subprocess) or an already-running remote server.

Resolution also had two entry points doing the same work: resolve_infra / ResolvedInfra / load_session are collapsed into load().
Models and MCP clients are built inside each load() call, which makes every call a fully isolated session instead of sharing process-wide infra. strands-compose load is now synchronous and reports what it wired.

Fixed along the way: transport auto-detection for url:, the ANSI renderer reading a non-existent message key on ERROR events, and strands-compose check printing session: None for built-in session providers (which only populate provider).

2. Drop tool_labels, close silent gaps in loading and rendering

tool_labels let YAML rename a tool for display. Display naming is a renderer concern, and the auto-generated "Delegating work to agent: X" labels hid the actual tool name the LLM invoked — the one thing a reader of the stream needs.
Removed from the agent schema, EventPublisher, and make_event_queue; the renderer now always shows the real name.

Fixed:

• INTERRUPT events reached the ANSI renderer and produced no output, so a run waiting on human input looked hung.
• Directory tool specs (./tools/) used a flat glob despite docs promising recursion. Now walks the tree and skips segments starting with _ or ., so __pycache__/ and .venv/ are never imported.
• A Swarm's or Graph's entry_name was not counted as a node reference by the orchestration planner, so a nested orchestration used only as the entry could be built after its parent.
• resolve_conversation_manager raised bare ValueError; now ConfigurationError, matching every other resolver.

Related Issues

N/A

Type of Change

• Breaking change

YAML / API Impact

Breaking in both YAML and Python. No deprecation shims.

YAML keys removed — configs using them now fail schema validation:

• mcp_servers: (top level)
• server: on an mcp_clients: entry
• tool_labels: on an agent

Python exports removed from strands_compose:

• MCPServerDef, create_mcp_server, MCPLifecycle
• ResolvedInfra, resolve_infra, load_session
• tool_labels= parameter on EventPublisher and make_event_queue

Behaviour changes for code that still compiles:

• load() is the single entry point and builds models + MCP clients per call, so each call is an isolated session. Callers that relied on shared infra across sessions must restructure.
• strands-compose load is synchronous.
• Directory tool specs now load nested subdirectories, so an agent may pick up more tools than before.

Minimum strands-agents is now >=1.52.0.

Testing

How have you tested the change?

• I ran uv run just check (lint + type check)
• I ran uv run just test for overall testing
• I added or updated tests that prove my fix is effective or my feature works
• I verified existing examples in examples/ still work

Coverage gate raised to 80%. Suite pruned of tests asserting framework behaviour or
duplicating coverage; added a parametrized test that fails if any EventType lacks a
renderer handler, and directory-recursion tests including same-stem files in sibling
subdirectories.

Checklist

• I have read the CONTRIBUTING document
• I have updated the documentation accordingly
• My changes generate no new warnings
• Any dependent changes have been merged and published

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