getBootstrapContent() called fs.existsSync + fs.readFileSync + regex
frontmatter parsing on every agent step with zero caching. The
experimental.chat.messages.transform hook fires every step in opencode's
agent loop (messages are reloaded from DB each step via
filterCompactedEffect). A 10-step turn triggered 10 redundant file
reads + 10 regex parses for content that never changes during a session.
Changes:
- Add module-level _bootstrapCache (undefined = not loaded, null = file
missing) so the first call reads and parses SKILL.md, all subsequent
calls return the cached string with zero filesystem access
- Cache the null sentinel when SKILL.md is missing, preventing repeated
fs.existsSync probes
- Add _testing export (resetCache/getCache) for test infrastructure
- Clarify the injection guard comment explaining how it interacts with
opencode's per-step message reloading
- Add 15 regression tests covering cache behavior, fs call counts,
injection guard, missing file sentinel, cache reset, and source audit
Fixes#1202
