Tag command stdout/stderr as command_output_message

[jackcbrown89]

Summary

• Introduces a command_output_message wire type so command stdout/stderr is no longer conflated with agent assistant_message text. Each chunk carries stream ("stdout"/"stderr"), text, and the originating command.
• Python client adds on_command_output to QueryOptions and ExecuteCommandsOptions. on_assistant_message continues to carry agent text only.
• Both runtimeuse and runtimeuse-client bumped 0.13.0 → 0.14.0.

Why

When pre/post commands or execute_commands produce output, callers currently can't tell command stdout/stderr apart from agent reasoning, can't tell stdout from stderr, and can't tie a chunk back to the command that produced it. This blocks per-command logging policies (e.g. routing setup-command output somewhere different from agent text).

Test plan

• TS: npm test in packages/runtimeuse — 143/143 pass
• TS: npm run typecheck — clean
• Python: uv run pytest test/test_client.py -q — 47/47 pass (3 new tests in TestCommandOutputMessage)
• Imports / instantiation smoke-test of CommandOutputMessageInterface, OnCommandOutputCallback, on_command_output field

Notes

• assistant_message is unchanged and still used by agent handlers via MessageSender.sendAssistantMessage.
• Old clients that only listen on on_assistant_message will no longer see command output (they'd previously get it disguised as agent text). That's the intended cleanup; pair any consumer upgrade with wiring on_command_output.
• silent flag is not added — visibility decisions move to the receiver via on_command_output.

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Note

Medium Risk
Medium risk because it changes the wire protocol and client callback surface for streamed command output; older clients listening only to assistant_message will stop seeing pre/post/command-only output unless updated.

Overview
Introduces a new command_output_message wire type so stdout/stderr from pre/post-invocation commands and execute_commands is no longer sent as assistant_message, and now includes stream (stdout/stderr), text, and originating command.

Updates the Python client to handle and expose this via a new on_command_output callback (with a lightweight hot-path dispatch), adds CommandOutputMessageInterface/OnCommandOutputCallback, and adjusts tests/examples/docs accordingly. Bumps both runtimeuse and runtimeuse-client versions to 0.14.0.

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