feat(delegate): wire agent connections through Agent.as_tool

[galuszkm]

Description

Delegate connections to an agent now go through strands.Agent.as_tool() instead of a hand-rolled @tool wrapper. The wrapper's biggest problem was interrupts: it turned a sub-agent's interrupt into an empty success, so a pending approval looked granted to the coordinator. Agent.as_tool() propagates the interrupt properly and lets it be answered and resumed.

That native adapter also owns preserve_context, so it's now exposed as connections[].preserve_context on a delegate connection. Setting it false resets the delegate to its construction-time baseline before every call — the only way to bound a stateless delegate's history in a long-lived session, since orchestrations share one live agent object across calls. It's rejected for a connection to a nested orchestration (no baseline to reset to) and for an agent carrying a session manager (persisting and wiping every call are contradictory) — both left to surface as-is rather than reimplemented, so the messages stay accurate if upstream's rules ever change.

A Swarm/Graph target has no as_tool() upstream, so it keeps a single hand-rolled wrapper (multiagent_as_tool, replacing node_as_tool/node_as_async_tool), which now also reports an interrupt raised inside the orchestration as a tool error instead of silently succeeding.

Also in this PR:

• extract_block_text reads citationsContent blocks, so a cited answer's text now crosses the delegation boundary instead of being dropped
• the converters package (StreamConverter, OpenAIStreamConverter, RawStreamConverter) is removed — framing StreamEvents into a wire format is a transport-layer concern, not something this library should own
• strands-agents floor bumped to 1.52.0 for the as_tool() behaviour this relies on

Related Issues

N/A

Type of Change

• Breaking change

YAML / API Impact

Config schema:

• new field connections[].preserve_context: bool (default true) on delegate connections

Public Python API (strands_compose):

• removed: node_as_tool, node_as_async_tool
• added: multiagent_as_tool (replaces both for Swarm/Graph targets; an Agent target now goes through strands.Agent.as_tool() directly)
• removed: strands_compose.converters (StreamConverter, OpenAIStreamConverter, RawStreamConverter)

Not backwards-compatible: any code importing node_as_tool, node_as_async_tool, or strands_compose.converters breaks. A delegate tool's result now carries text blocks only (previously also image/document/json, which a model cannot itself emit into its own final message, so this had no live use). Requires strands-agents>=1.52.0,<2.0.0.

Testing

• 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

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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