Now I remember the theme

openspec/specs/interaction-tracking-taxonomy/spec.md

@@ -133,3 +133,25 @@ The taxonomy MUST prohibit including personally identifiable information (PII) i
 #### Scenario: Tracking includes only categorical metadata
 - **WHEN** tracking metadata is defined for a clickable item
 - **THEN** it contains only categorical identifiers (ids, placements, domains) and does not include user-provided content
+
+### Requirement: Theme switch event taxonomy
+The tracking taxonomy MUST define an event for theme switching.
+
+The event name MUST be `theme_switch`.
+
+The `theme_switch` event MUST include, at minimum:
+- `target_id`
+- `placement`
+- `theme`
+
+The event MUST include `prev_theme` when it is available.
+
+The taxonomy MUST define the `target_id` namespace for theme switching as:
+- `theme.switch.<theme>`
+
+The taxonomy MUST define the `placement` value for the theme switcher notch as:
+- `theme_notch`
+
+#### Scenario: Theme switch target_id is deterministic
+- **WHEN** a user selects `light` theme using the theme notch
+- **THEN** the event is emitted with `target_id=theme.switch.light` and `placement=theme_notch`