Codex flagged: the previous fix (b3180534) read
\`doc.themes[SEMANTIC_PALETTE_THEME_AXIS]\` as the dark-mode
discriminator, but \`seedDocVariablesFromStyleGuide\` — the only
production writer of theme-related doc state — writes ONLY
\`doc.variables\`, never \`doc.themes\`. So on a real
orchestrator-emitted dark-mode design the axis is empty, the test
\`modeAxis[0] === 'Dark'\` is false, and the cascade still served
the LIGHT palette. The "production" dark-mode signal was wired to
nothing.
Fix reads the active page root's fill via \`detectThemeFromNode\`, the
same heuristic \`resolveTreeRoles\` uses at its entry point to set
\`ctx.theme\` for role defaults. The page root's fill is what the
model / user actually painted as the page background, regardless
of whether any themes axis was ever populated, so it's the
production-truthful signal.
New \`detectActivePageMode()\` helper reads the doc store + canvas
store's activePageId, finds the first frame on that page, and
runs \`detectThemeFromNode\`. Defaults to 'light' when no page root
exists or it has no fill — same conservative bias as before.
Test updated to seed a dark page-root fill on the live doc store
(replaces the prior \`themes['Mode']\` axis seed which never
matched production state). Also explicitly nulls the themes axis
to confirm the fill-based detection is the active code path.
2e577b9b00