Now I remember the theme

openspec/changes/archive/2026-02-11-remember-theme/proposal.md

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+## Why
+
+Theme choice is part of a user's identity and comfort on the site; returning visitors should land in the theme they previously selected. We also need measurement to understand whether the theme switcher is being used and which themes are preferred.
+
+## What Changes
+
+- Persist the user's selected theme across visits so returning users see the last-selected theme immediately.
+- Add Umami tracking for theme selection changes so theme switch usage can be measured and segmented.
+- Improve robustness of persistence by supporting either localStorage or a client-side cookie (cookie fallback when localStorage is unavailable).
+
+## Capabilities
+
+### New Capabilities
+- (none)
+
+### Modified Capabilities
+- `site-theming`: Extend theme persistence requirements to explicitly cover returning visits and define acceptable client-side persistence mechanisms / fallback behavior.
+- `analytics-umami`: Add a custom event emitted from client-side code for theme selection changes (using Umami's JS API when needed).
+- `interaction-tracking-taxonomy`: Define the theme selection event name and required event properties (at minimum `target_id` and `placement`, plus theme metadata).
+
+## Impact
+
+- Frontend: update theme switcher behavior in `site/src/layouts/BaseLayout.astro` (persistence/fallback and event emission).
+- Analytics: new Umami event(s) added; dashboards/filters can segment by selected theme and placement.
+- Specs: update the modified capabilities above to reflect the new requirements.