stdout-is-protocol compositions have no diagnostics channel: logger-console writes to stdout only — request a stderr exporter

[jiaoqsh]

Summary

Compositions serving the stdio JSON-RPC SDK (dsh-sdk-jsonrpc-server) reserve
stdout for protocol frames. The
jsonrpc-demo README
says it plainly:

stdout carries only JSON-RPC frames. The bin and boot guards diagnose on stderr, and the config must omit stdout loggers.

But the only in-tree log exporter (cordis-plugin-logger-console) renders via
console.log, i.e. stdout. The two rules together mean an SDK-serving
composition cannot mount any logger — every plugin-level diagnostic simply
vanishes. The bin's own boot guards reach stderr; nothing after boot does.

What that costs in practice

Integrating the SDK runtime, we debugged two separate incidents where the only
observable symptom was "the model doesn't have the tools":

• an MCP server rejecting connections (auth header drift) — connect failures
  logged nowhere, stderr empty, the harness otherwise healthy;
• the tool-registration timing race (filed separately) — indistinguishable from
  the auth failure without instrumenting the runtime by hand.

#314 reports the same class of pain on the web profile: a silently-failing
streamable-http transport with "no error surfaced". For stdio SDK
compositions it is structurally guaranteed — there is nowhere for the error to
go.

Ask

Either of:

1. A stream target option on ConsoleExporter (e.g.
   target: 'stdout' | 'stderr'), so SDK compositions can mount
   logger-console pointed at stderr; or
2. A dedicated stderr exporter plugin.

The SDK client side is already prepared for this: the Python SDK captures a
stderr tail and attaches it to transport-failure diagnostics — today that tail
is almost always empty precisely because nothing in the composition can write
to it.

Environment

@deepseek-ai/dsh-* 0.1.0-rc.6, stdio JSON-RPC composition
(packaged-bin.js, Node 22.19), macOS 15.

[kunwar-vp]

+1 — this gap turns other bugs into silent ones. Concrete case: mcp-client's registration-failure path logs through ctx.logger.error, but in a stdout-is-protocol composition with no logger mounted, that error goes nowhere. Combined with the boot race in #1239, the observable behavior is just "the model has no MCP tools and nobody knows why." A minimal stderr exporter shipped in the default jsonrpc composition would have turned a multi-hour debug into a one-line log read.