4b - review nits: the list's headroom folds into its item loop, emitBlocks inlined, panel-wrapped boundary pinned, 4c note says cubic

todo.md

@@ -64,11 +64,9 @@ proves 12, 13 spells 11's gaps in 12's grammar, and 12 rewrites code 4b and 4c c
       export persona runs in bulk walks the document twice. Both walks are linear, so this is a
       constant factor rather than 4b's class change, and the parting is what gives depth its own
       code (§8) — measure before joining them back.
-      **Settled** (the maintainer, 2026-09-18): the limit stays 500 readable lists. The one walk
-      counts items one below the list, as the readable form does, and reports its headroom; a
-      list falling back to the directive form refuses when that form's extra level no longer
-      fits. Counting every list twice was rejected for halving the limit, counting the directive
-      form once for doubling the parser's frames per level.
+      **Settled** (the maintainer, 2026-09-18): the limit stays 500 readable lists, the walk
+      reporting its headroom (§11). Counting every list twice was rejected for halving the limit,
+      counting the directive form once for doubling the parser's frames per level.
       **Measured** (2026-09-18): `adfDocumentFault` walks a 9 MB document in 52 ms against 314 ms
       for the emit, so its two walks stay parted.
 - [ ] **4c — The scanning rule's remaining sites (`0.2.0`).** A trailing-anchored regex re-walks
@@ -90,9 +88,10 @@ proves 12, 13 spells 11's gaps in 12's grammar, and 12 rewrites code 4b and 4c c
       `readDirectiveContent`'s scan splits into named steps with that fix rather than keeping its
       complexity (the maintainer, 2026-09-16). A sixth 4b leaves behind: the parser asks
       `commonMarkSpelling` at every directive-spelled list it reads, and the answer spells the whole
-      subtree below, so nested directive lists cost O(depth × subtree) — 250 rule-first levels parse
-      in 1.3 s at 16.5 kB, 1.5 MB of that shape at 250 levels in 0.6 s — bounded by the depth guard like
-      `readNestedDirective` (the maintainer, 2026-09-18).
+      subtree below, itself quadratic in the depth left, so nested directive lists cost about the
+      cube of their depth — 250 rule-first levels parse in 1.3 s at 16.5 kB, 1.5 MB of that shape
+      at 250 levels in 0.6 s — bounded by the depth guard like `readNestedDirective` (the
+      maintainer, 2026-09-18).
 - [ ] **4d — What the gate says while it runs (`0.2.1`).** `ci.sh` runs nine legs and announces
       none of them, so five minutes of a Gitea run read as silence and a hang cannot be told from
       a slow pull — the maintainer hit exactly this on the `0.1.0` release. Three causes, each its