COHERENCE.md §14's last missing workbench primitive. Q#TR1-TR4 decided
at review; this implements them.
EXTENDS LISTVIEW rather than adding a treeview (Q#TR1). A separate
primitive would either duplicate ~200 lines of panel discipline —
Q#GB18 handle identity, Q#GB13 `<2>` disambiguation, the read-only
intercept, `prev` capture, the quit chain, generated-buffer writes — or
require extracting them from a shipped primitive first, which is the
riskier change. Rows gain OPTIONAL `depth` and `id`; absent, they behave
exactly as before, which is what keeps the three flat consumers
untouched.
THE OBSERVATION THAT MADE THIS CHEAP: collapse only ever HIDES rows and
never changes a surviving row's depth. Combined with consumers emitting
parents before children in document order, a node's descendants are a
CONTIGUOUS RUN of following rows with greater depth. So collapse is
filtering an existing array, not re-deriving one — the primitive never
calls the consumer to re-render a fold, and pre-rendered indentation
stays correct. That is why `text` remains consumer-supplied (Q#TR4),
which also sidesteps the future conflict with dired's fixed-width
`_layout` column contract.
It is also why a panel with NO `on_refresh` can still fold. The anchor
consumer is exactly that panel: the outline has no refresh at all
(framing §1.5a), so a design requiring the consumer to re-supply rows on
every fold would not have worked for the only consumer that exists.
SELECTION IS RE-SEATED BY ID, NOT BY LINE (Q#TR3). A fold inserts or
removes rows above the cursor, so a line-keyed restore lands on an
unrelated node — the defect `listview.refresh` already had in milder
form. `id` is consumer-supplied and compared by equality; the primitive
never derives one. The outline uses `line:col`, unique per document and
stable across re-render, rather than the `::` parent chain, which
collides on overloads and same-named siblings — precisely where a stale
expansion would reattach to the wrong node.
`has_children` reads the FULL row array rather than the rendered subset.
A collapsed node's children are absent from `line_to_row` by
construction, so asking the rendered view would answer "no" for every
collapsed node and make expanding impossible.
TAB ON A LEAF REPORTS rather than silently doing nothing. The outline's
`g` is already a dead binding — bound, dispatched, no feedback — and
this primitive must not add a second one.
Tests: fold hides ALL descendants while the node and its SIBLING
survive; state and selection survive a re-render; a leaf reports; and a
depthless panel is unchanged by TAB. The fold test is bite-verified —
disabling only the ancestor filter fails it on "descendants hidden".
Verified: fmt, diff-check, clippy with and without crdt, --lib 1896, m4
149, listview 21/21, and the full serialized luajit sweep at 3453
passed / 0 failed. That count reconciles exactly: main is 3450 (Stage
3's 3449 sweep predated its capability-fallback pin) plus these three
tests.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Levi Neuwirth
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