fix: header reflows under enlarged text; reopen the step-1 nowrap decision

The step-1 header decision is formally reopened (AGENTS.md (ak)): its record
attributed the residual to the wrong cause and read a measured 944px functional
failure as a robustness margin.

Mechanism — wrapping, plus a gated sticky offset:
- `flex-wrap: nowrap` removed from `.header-inner` (measured necessary AND
  sufficient) and from `.nav-list` (measured inert; removed so the prohibition
  is not contradicted by a `nowrap` in the same file), with a dead `flex: none`.
- `inset-block-start` becomes a two-band, two-term saturating clamp() so the
  header is sticky only while the masthead is one row. A media query cannot
  express this: its `rem` resolves against the browser DEFAULT font size, a
  property's against the root element. The second term catches a root BELOW the
  default, where the 80rem content cap shrinks faster than the header's px
  minimums; without it 65px of `#main` sat behind the header at 9px.
- Wrapping is the only mechanism that reflows under all THREE enlargement paths,
  because Chrome's minimum-font-size setting is invisible to @media, to
  @container and to every length unit.

Measured, 22 pages x 16 widths = 352 page-widths per method:
  root-style 32px        175/352 -> 0/352   (1280px: 944px overflow -> 0)
  minimum-font-size 32   219/352 -> 88/352  (residual is the footer email)
  default-font-size 32     0/352 -> 0/352
  default (root 16)        0/352 -> 0/352
Nav items and CTA on-screen in 1408/1408. A further 762 points across roots
9-32, both thresholds, the band seam and all five Chrome presets: 0 failing.

Normal-settings identity: 0 differences on 352 page-widths across six metrics,
with six nav items and with a seventh injected. Header 81.00px at all eight
widths >= 1056, CTA gap 0.00px. Lighthouse: 22 pages, no category below 95,
CLS 0.000 on every page.

--header-h is reworded as a FLOOR, not a constant; value unchanged.

Also in this step, per ruling:
- /bio/ print `font-weight` frozen at 400 — the circulated PDF's typography
  changes only when its content is deliberately revised, never as a side effect
  of a screen refactor. Declaration byte-identical; the constraint is recorded.
- CLAUDE.md: the two-simulation rule for enlarged text, the zsh
  no-word-splitting rule, the third (minimum-font-size) mechanism, and
  "state the grid with the count".

Two rounds of adversarial-reviewer, eleven findings, all resolved; round 2's
blocking finding was a defect in round 1's own fix. Two suggested fixes declined
with reasons in (ak). claims-auditor deliberately not run — D20.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Md3GndFqWPzK78xAoebsg5

src/styles/global.css

@@ -121,7 +121,11 @@ html {
 /* The header is sticky from 66rem up, and `scroll-padding-top` has to clear it
    or "Skip to content" drops the reader behind it — the one control that exists
    specifically for keyboard users, landing them on content they cannot see.
-   --header-h is defined in tokens.css beside the value it has to match.      */
+   `--header-h` is defined in tokens.css beside the value it has to match, and it
+   is a FLOOR — above the default text size the masthead reflows and is taller, and
+   `SiteHeader` gates stickiness so the offset is generous rather than short.
+   ⚠️ TWO SETTINGS DEFEAT THAT GATE and leave this offset short; `docs/02` §Reflow
+   names them and shows why no CSS can detect either.                         */
 @media (min-width: 66rem) {
   html {
     scroll-padding-top: calc(var(--header-h) + var(--space-4));

src/styles/tokens.css

@@ -137,15 +137,20 @@
 
   /* --- Layout ------------------------------------------------------------ */
 
-  /* Sticky-header height at >= 66rem, where the header IS sticky. global.css
-     drives `scroll-padding-top` off this, so the skip link does not drop the
-     reader behind the header. If SiteHeader's padding or nav sizing changes,
-     re-measure and change this with it — one fact living in two files.
-     [measured 2026-08-26 — headless Chrome at 1024/1100/1280/1440px, with six
-      nav items and with a seventh injected. 81px at every one: 32 padding + 48
-      reserved brand block + the 1px bottom border, which is easy to forget and
-      is why this is measured rather than added up. The brand reserves 48px so
-      the height does not change when the tagline appears at 76rem]            */
+  /* ⚠️ A FLOOR, NOT A CONSTANT: the sticky header's height AT THE DEFAULT TEXT
+     SIZE. Above the default the masthead reflows and is deliberately taller, which
+     is why the nav no longer runs off-screen. `global.css` drives
+     `scroll-padding-top` off it and `SiteHeader` gates stickiness so the offset is
+     generous rather than short — **but not in every case**: `docs/02` §Reflow lists
+     the two settings where it is still short and why no CSS can see them. If
+     SiteHeader's padding or nav sizing changes, re-measure and change this with
+     it — one fact living in two files.
+     [measured 2026-08-26, re-measured 2026-09-01 — headless Chrome, six nav items
+      and a seventh injected. 81.00px at all EIGHT widths from 1056 to 1920px
+      (1056/1100/1216/1240/1280/1440/1600/1920): 32 padding + 48 reserved brand
+      block + the 1px bottom border, which is easy to forget and is why this is
+      measured rather than added up. The brand reserves 48px so the height does not
+      change when the tagline appears at 76rem]                                 */
   --header-h: 5.0625rem;    /* 81 — measured, not chosen */
 
   --width-content: 80rem;   /* 1280 */