The previous "navbar in PROTECTED_ROLES" change was Codex-flagged as a
no-op: PROTECTED_ROLES only PREVENTS strip-pass deletion of an existing
fill, it doesn't ADD one. The actual food-app brief failure was that the
sub-agent emitted a bottom navigation row WITHOUT any fill at all,
relying on the parent surface for visual contrast — but the parent (the
cream root frame) doesn't supply that contrast, so the nav blends
straight into the cream background and visually disappears.
New deterministic pass: `injectMissingNavSurfaceFill`. For each direct
child of the page root whose role is one of {navbar, nav, tab-bar,
bottom-tab-bar, top-nav-bar, top-app-bar, tab-row} AND whose fill is
empty/missing, set `fill = [{type: solid, color: '$color-surface'}]`
so the renderer resolves it through the seeded palette and the nav
gets a visible white surface separation from the cream root.
Scope contract:
- Only direct children of the passed root frame (page root). Nav frames
nested inside cards / sections / banners are left alone.
- Never overrides an existing fill — sub-agent intent (e.g. an
intentionally dark `top-app-bar`) is preserved.
- Pure mutation; returns `true` when any nav was patched.
Wired into the same hook point as `stripRedundantSectionFills` (via
`design-canvas-ops.ts::generationCleanup`), so every generation cycle
sees both a strip pass (remove hedge fills) and an inject pass (add
the missing nav surface). Five new tests cover all nav role variants,
preservation of existing fills, scope (no recurse into cards), and
no-op on unrelated roles.
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