venue: adopt the videre logging capability, retire the cow-venue stderr sink

[mfw78]

Problem. nullislabs/videre-nexum-module#26 admits the logging capability to the venue-adapter world (opt-in per adapter, host import wired in the venue store linker, module-world impl reused). cow-venue still carries the stderr-backed tracing sink workaround installed in init: unstructured, no levels, no fields, per-line WARN host-side.

Scope.

• Bump the videre rev once venue: admit the logging capability to the venue-adapter world videre-nexum-module#26 merges.
• Declare logging in cow-venue's module.toml and install the standard nexum_sdk tracing facade in init.
• Remove the stderr-sink workaround.
• Confirm cow-venue tracing events reach the host pipeline with level and target intact.

Dependencies. nullislabs/videre-nexum-module#26 merged and revved.

AI Assistance: Claude Fable filed this follow-up from the videre#26 design (videre-only scope decision).

[mfw78]

Blocked on an upstream gap found while red-teaming nullislabs/videre-nexum-module#26: nullislabs/nexum-runtime#76.

PROVIDER_CAPABILITIES in nexum-runtime carries only chain and messaging, so the scope item "Declare logging in cow-venue's module.toml" fails at Supervisor::boot with unknown capability "logging" in [capabilities]. The rest of the path works: the venue world synthesis emits the import, the venue store linker binds it, and guest tracing events reach the host LogRouter at their own level with fields rendered into the message. Only the manifest declaration is unrepresentable.

Order of work: land nexum-runtime#76, bump the runtime pin in videre, then bump the videre rev here and declare the capability.

One correction to the last scope item. nexum:host/logging.log takes (level, message) and LogRecord has no target field, so "level and target intact" is not reachable without a WIT vocabulary change, which videre#26 ruled a non-goal. The facade renders structured fields into the message (msg key=value ...), so what is verifiable is level and fields intact. Suggest restating the item that way, or filing the target-forwarding WIT change separately.

[mfw78]

Blocked by nullislabs/nexum-runtime#77: the pinned runtime refuses logging in a provider manifest, so the cow-venue facade swap cannot land until that admits the capability. Note also the target-field limitation recorded there.

[mfw78]

Correction: the upstream blocker is nullislabs/nexum-runtime#76 (nexum-runtime#77 was a duplicate, now closed).