agent-doc-core — document data layer for agent-doc.
See tasks/agent-doc/plan-agent-doc-core-extraction.md for the wave plan.
Currently extracted: Wave 1 (id, crdt, component, model_tier, pending),
Wave 2 (frontmatter, project_config), Wave 3 (template), Wave 4 (diff
pure half per #rtx6 Option 1 — ComputeResult, compute,
compute_with_current, wait_for_stable_content, run stay in the main
crate's diff_io.rs because they call snapshot::{load,save,resolve, path_for}). Some functions in frontmatter, project_config, and
template take &Path and touch the filesystem — they live here for the
convenience of a single move and may be split into orchestration wrappers
in a follow-up tidy.