docs(webview): record the narrowed TABLE-DELIM arm and its measurement

Correct the field headers to describe the delta-based TABLE-DELIM arm
instead of the old presence-based one: table-skeleton.ts's PERF
paragraph now explains that only a delimiter row completing/breaking
or a cell-count change takes the full walk, and image-field.ts drops
the false 'a table cell' entry from its list of SHAPE-only regressing
classes.

Repair the two cm-table-skeleton.test.ts comments whose stated reason
('the line carries a |') stopped being true once TABLE-DELIM became a
per-line shape delta; the offsets and negative pins they document are
unchanged.

PERF.md, PERF-log.md, LEARNING.md and TODO.md are updated in the
separate local-only .claude/ tree (per this repo's TODO-local-mode
convention) and are not part of this commit.

Author: mtskf

src/webview/cm/image/image-field.ts

@@ -62,13 +62,16 @@
 // which G2 alone cannot see. Rationale + the check itself live in that file, which also
 // owns the roster of bounded fields that keep a NARROWER structural predicate of their own
 // instead; no copy of that roster is kept here, because a copy goes stale the next time one
-// of them moves. ⚠️ PERF: that structural term is PRESENCE-based over the whole changed
-// line, so typing in the body of a list item, a blockquote line, a table cell or an ATX
-// heading — and every Enter — now takes the full walk this field's bounding exists to
-// avoid. THIS field's own full-walk cost was measured at 0.71–0.75 ms/keystroke (19 KB /
-// 150 block images and 154 KB / 1200 block images) — essentially flat in document size,
-// which the table field's is NOT, so neither field's number may be inferred from the
-// other's. Accepted on that measurement, not free: see PERF.md.
+// of them moves. ⚠️ PERF: that structural term's SHAPE arm is still PRESENCE-based over
+// the whole changed line, so typing in the body of a list item, a blockquote line, or an
+// ATX heading — and every Enter — still takes the full walk this field's bounding exists
+// to avoid. Its TABLE-DELIM arm is NOT presence-based (a per-line SHAPE-DELTA,
+// `tableRowShapeChanged`), so this field no longer full-rebuilds merely because a `|` sits
+// somewhere else in the document. THIS field's own full-walk cost was measured at
+// 0.71–0.75 ms/keystroke (19 KB / 150 block images and 154 KB / 1200 block images) —
+// essentially flat in document size, which the table field's is NOT, so neither field's
+// number may be inferred from the other's. Accepted on that measurement, not free: see
+// PERF.md.
 // A reused widget whose document position SHIFTED is reconstructed with the new
 // docFrom (cheap: same alt/safeUrl/slice, NO re-parse). The small pure leaf
 // helpers (mergeIntervals / lineExpandWithNeighbours / intersects /

src/webview/cm/table/table-skeleton.ts

@@ -24,12 +24,16 @@
 // which ORs G2 (an incomplete post-edit frontier → full walk; the later
 // background-parse publication, a `!docChanged` tree-identity change, full-walks
 // again to self-heal) with G-STRUCT (a structural reparse re-shapes boundaries
-// outside the span with a complete frontier → full walk). ⚠️ PERF: G-STRUCT is
-// PRESENCE-based over the whole changed line, and a table cell's line always
-// carries a `|`, so typing INSIDE a cell takes the full walk — exactly the
-// whole-tree materialisation + per-table `parseTable` this field exists to skip.
-// Measured and accepted, not free: see PERF.md. Soundness (bounded ≡ fullWalk,
-// ranges AND parses) is pinned by cm-table-skeleton.test.ts.
+// outside the span with a complete frontier → full walk). ⚠️ PERF: G-STRUCT's
+// TABLE-DELIM arm is a per-line SHAPE-DELTA (`tableRowShapeChanged`), not a
+// presence test over the whole changed line, so typing INSIDE a cell whose row
+// shape is unchanged stays on the bounded path this field exists to protect —
+// only a delimiter row completing/breaking or a header's cell count changing
+// takes the full walk. G-STRUCT's OTHER arm (SHAPE) is still presence-based, so
+// a list-item body, a blockquote line, an ATX heading, or any Enter still takes
+// the full walk regardless of this field. Measured and accepted, not free: see
+// PERF.md. Soundness (bounded ≡ fullWalk, ranges AND parses) is pinned by
+// cm-table-skeleton.test.ts.
 
 import { syntaxTree } from "@codemirror/language";
 import { type EditorState, StateField, type Transaction } from "@codemirror/state";

test/webview/table/cm-table-skeleton.test.ts

@@ -163,11 +163,14 @@ describe("tableSkeletonField bounded ≡ fullWalk", () => {
       mount: (parent) =>
         settledMount({ state: EditorState.create({ doc, extensions: exts() }), parent }, 10_000),
       observe: (view, requireUnstarvedFrontier) => {
-        // Offset chosen to land INSIDE the `prose` paragraph. The offset is load-bearing:
-        // an edit on either table's own lines carries a `|`, which trips the structural
-        // guard's TABLE-DELIM arm and routes the dispatch to the FULL walk — leaving this
-        // test comparing full against full and unable to see a broken boundedUpdate. The
-        // negative pin below is what keeps that from drifting back silently.
+        // Offset chosen to land INSIDE the `prose` paragraph, i.e. OUTSIDE both tables'
+        // node ranges. That is what keeps this test on the REUSE half of `boundedUpdate`
+        // (the sibling below puts the edit's span ON a table to exercise the RE-WALK half
+        // instead) — it is no longer about pipe presence: the narrowed TABLE-DELIM arm is
+        // a per-line SHAPE delta (`tableRowShapeChanged`), not "any `|` on the line", so an
+        // in-cell keystroke that leaves a row's shape unchanged stays on the bounded arm
+        // too. The negative pin below still guards against a regression that would route
+        // this specific edit to the FULL walk.
         const proseAt = doc.indexOf("prose") + 2;
         const tr = view.state.update({ changes: { from: proseAt, insert: "x" } });
         expect(touchesStructuralReparse(tr)).toBe(false); // this edit really is on the bounded arm
@@ -204,9 +207,10 @@ describe("tableSkeletonField bounded ≡ fullWalk", () => {
       mount: (parent) =>
         settledMount({ state: EditorState.create({ doc, extensions: exts() }), parent }, 10_000),
       observe: (view, requireUnstarvedFrontier) => {
-        // End of `intro` — prose, so the changed line carries no `|` and no structural
-        // shape. The negative pin keeps that from drifting into the FULL arm, where this
-        // would compare a full walk against a full walk.
+        // End of `intro` — prose, with no table-shape signal (no `|`, no delimiter row, no
+        // cell-count change) for the narrowed TABLE-DELIM arm to fire on, and no other
+        // structural shape either. The negative pin keeps that from drifting into the FULL
+        // arm, where this would compare a full walk against a full walk.
         const tr = view.state.update({ changes: { from: 5, insert: "X" } });
         expect(touchesStructuralReparse(tr)).toBe(false);
         view.dispatch(tr);