Verify and fix Kimaki/OpenCode runtime signature attribution env vars

[chubes4]

Problem

Latest wp-coding-agents registers runtime signatures for KIMAKI_SESSION_ID, KIMAKI_THREAD_ID, KIMAKI_THREAD_URL, OPENCODE_SESSION_ID, and OPENCODE_RUN_ID. In Kimaki 0.13.0 source review, the Kimaki-specific env vars were not found, and the current live Kimaki session exposes OPENCODE_RUN_ID but not OPENCODE_SESSION_ID or the KIMAKI_* thread/session vars.

This means the new worktree attribution registry may publish dead env-var contracts.

Scope

• Reproduce against Kimaki 0.13.0 runtime, not just source inspection.
• Determine the real env vars available to agent tool processes and worktree-creating commands.
• Fix wp-coding-agents runtime signature registration/docs/tests to match reality.
• If attribution requires new Kimaki support, file or implement the upstream Kimaki change first, then update wp-coding-agents.

Acceptance criteria

• Runtime signature docs and mu-plugin registration only include vars that are actually exported.
• Tests cover the registered signature map.
• If upstream Kimaki support is required, the wp-coding-agents PR links the upstream issue/PR and does not claim unsupported env vars work.

AI assistance

This issue was identified during an OpenCode GPT-5.5 review of wp-coding-agents against Kimaki 0.13.0.