Name a failed step's index in drawSteps' panics, and quote the decision's measurement as the experiment it was

docs/decisions.md

@@ -591,7 +591,7 @@ is until a real data set needs the indexed form.
 2026-09-17, Lilleman auf Larv.
 
 A path that fails below its first level then moves no seeded stream, at the cost of one
-draw-free walk per call, which allocates nothing.
+draw-free walk per call, which allocates nothing up to 16 steps.
 
 ## A country's postal codes and streets are siblings under its locality
 
@@ -848,8 +848,9 @@ the direct chain is the one a reader can predict from the tables' parents.
 replaces "The path walks are separate loops".
 Goals 2 and 11: `drawSteps` draws every path from its steps, compiled at link by
 `pathCheck` or, for a caller's path, by `probePath` into a stack buffer. The check and
-the probe stay two loops: one loop leaks the check's leaves and errors with the draw's
+the probe stay two loops: on 2026-09-29 one loop over all three walks, switching on a
-state, since Go tracks a struct's fields as one, and a repeat of a reference path rose
+mode field, leaked the check's leaves and errors with the draw's pins, arm and memo,
-from 66 to 106 allocations. `drawSteps` takes its state as parameters and a step holds
+since Go tracks a struct's fields as one, and a repeat of a reference path rose from 66
-no node, so no benchmark gained an allocation. Valid while Go's escape analysis tracks
+to 106 allocations. `drawSteps` takes its state as parameters and a step holds no node,
+so no benchmark gained an allocation. Valid while Go's escape analysis tracks
 a struct's fields as one.

path.go

@@ -187,7 +187,8 @@ func (t *table) route(tail []string, descended bool) (tableRoute, error) {
 }
 
 // pathStep is one step of a compiled path, taken at the node the steps before it
-// reached; at indexes the tail segment the step consumes. A step holds no node, so a
+// reached, a choice there resolved first; at indexes the tail where it is taken, and
+// only a table's step sits past the tail's end. A step holds no node, so a
 // caller's steps stay on its stack.
 type pathStep struct {
 	kind stepKind
@@ -199,7 +200,7 @@ type pathStep struct {
 type stepKind uint8
 
 const (
-	stepField  stepKind = iota + 1 // into a field of the template at this level, a choice there resolved first
+	stepField  stepKind = iota + 1 // into a field of the template at this level
 	stepSelect                     // pin the selected row of the table
 	stepDraw                       // draw a row of the table inside the pins
 	stepRow                        // land on the table's row node
@@ -374,13 +375,13 @@ func drawSteps(s *generatorState, n node, steps []pathStep, pins *pinSet, memo *
 		if st.kind == stepField {
 			var err error
 			if n, err = stepInto(n, st.name); err != nil {
-				panic(internalError("%v; a path's steps should have been compiled from the node they are drawn from", err))
+				panic(internalError("step %d: %v; a path's steps should have been compiled from the node they are drawn from", st.at, err))
 			}
 			continue
 		}
 		t, ok := n.(*table)
 		if !ok {
-			panic(internalError("a table's step %q on %T", st.name, n))
+			panic(internalError("step %d: a table's step of kind %d on %T", st.at, st.kind, n))
 		}
 		n = t.drawStep(s, st, pins)
 	}