fix: inject affinity metadata on simple completion calls

[rjcloudsigma]

Root cause

The Snowcrash Server key had two simultaneous populations:

• plugin-wrapped full agent/tool runs: correlation metadata + stable oc: identity
• identity-less internal/background/simple completions: no metadata, fresh TaaS session per request

Both originate in the same OpenClaw gateway and use the same API key. The identity-less population was not Alien Studio or another host.

The plugin registered only wrapStreamFn. OpenClaw routes simple/internal/background completions through a separate runtime hook, wrapSimpleCompletionStreamFn, which therefore bypassed all affinity injection.

Fix

Register the existing buildWrapper on both surfaces. It injects identical metadata.session_id, metadata.sticky_key, requester runtime, and openclaw_correlation fields.

The runtime supports this hook; the currently installed plugin SDK type declaration lags the optional field, so a narrowly scoped compatibility cast is used at registration only.

Verification

• New simple-completion regression test drives the exact hook and asserts generated oc: session/sticky identity plus agent_id correlation.
• 17/17 plugin tests pass; TypeScript build clean.
• No change to native-session precedence or no-identity behaviour.