The fold engine behind `docs/folding-framing.md` (approved rev 5): a
per-buffer fold store, a structural tree-sitter fold source, the
state-aware Lua command + data-API surface with the Emacs hideshow
`C-c @` bindings, the dispatch-layer pre-edit unfold, and `FoldState`
production. No rendering — Stages 2 (grid) and 3 (GPU) consume the store.
- `src/fold.rs`: `FoldStore` (a buffer-attached `View` that translates
ranges on every edit and drops any whose head/tail the edit crosses,
provenance-blind — Q#FD6), the structural source (nearest block-like
node >= 2 source lines -> introducer<->body -> **derived head line**,
the line immediately above the first hidden line, so wrapped signatures
and `where` clauses stay visible per R3-1 -> **closer-aware tail**, a
closing-delimiter line stays visible per R2-5), injection-layer walk,
`(start, end]` containment, and the state-aware ops (close innermost
open / open outermost closed / org-TAB cycle). Stale/absent tree
refuses (Q#FD10).
- `src/lua_bindings/fold.rs`: `pmacs.fold.*` — explicit-buffer data API
(`fold`/`unfold`/`folds`/`toggle`) + interactive helpers, validation
(Q#FD11: document buffer, UTF-8 boundaries, >= 1 hidden line — Q#FD9
falls out of the last clause), point-moves-to-head (Q#FD3).
- `builtin/runtime/fold.lua`: `fold.toggle/close/open/close-all/open-all`
commands + the `C-c @` prefix set (Q#FD4).
- `src/editor_core.rs`: the six point-anchored edit primitives run the
pre-edit unfold keyed on the authenticated source's point (Q#FD5,
command path); `EditorCore` owns the shared `FoldRegistry`.
- `src/semantic_render.rs`: the `FoldState` producer —
authoritative-empty, diff-suppressed, baseline resets on
`BufferSnapshot` (Q#FD8); the "never emitted" pin split so
`BlockAdornments` stays unproduced.
- `tests/folding_acceptance.rs` (16) over real Rust/Python/markdown
grammars + `fold_state_producer_transitions` + 15 engine unit tests.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Q5BkezMppbpCgGAYk2ftxV
