diagnostics.otel.captureContent.{toolInputs,toolOutputs} were documented
and config-wired but never produced any span content. Emit tool args and
results over the trusted private-data diagnostic channel (mirroring the
model-content path), and have the OTel exporter bound/redact/truncate them
before span export. Raw tool content never rides the public event bus.
Scope: core embedded-runner tool path (canonical producer). Codex
(async-batched) and Claude CLI remain follow-ups tracked by the issue.
Refs #77391
bf95883812