core: project skills missing from session when instruction baseline is captured before config skill plugin loads

Project .opencode/skills/* are sometimes missing from a session's <available_skills> for the whole session, even though they load fine by ID and GET /api/skill lists them for the same location.

Cause: skill discovery is async (the location-scoped ConfigSkillPlugin in packages/core/src/config/plugin/skill.ts scans and registers after boot), but SkillInstructions.load (packages/core/src/skill/instructions.ts) snapshots Skill.list() during SessionContext.select without waiting for that scan. A session started before it completes freezes an incomplete baseline in instruction_state.initial_values that is never corrected.

OpenCode version: v2.0.10

Plugins: none

Steps to reproduce

1. In a project containing .opencode/skills/foo/SKILL.md, start a session in a location that has not booted yet.
2. The session's <available_skills> omits foo and stays that way.
3. Later in the same location, GET /api/skill?location[directory]=<dir> lists foo.

Direct evidence of the race — same fresh directory, repeated calls:

call 1 -> []
call 2 -> ['opencode','report']
call 3 -> ['browser','opencode','openwebui-backend-testing','openwebui-fork-deploy']

Affected sessions have instruction_state.initial_values containing only built-in skills (or built-ins plus global skills), with through_seq frozen at the first step and no instruction_entry rows. Intermittent: some sessions in the same project captured the full list.

Operating System: Linux 6.18.33.2-microsoft-standard-WSL2 (WSL2)

Terminal: xterm-256color

Start with packages/core/src/config/plugin/skill.ts and packages/core/src/skill/instructions.ts, then trace SessionContext.select and the Skill.list() call. Reproduce in a fresh project location using the provided repeated-call sequence. Done means a session started before discovery completes retains the project skill in its available_skills for the whole session.