## ADDED Requirements

### Requirement: Keyboard handler uses stable selectedSpanId
The SpanAnnotationManager keyboard handler SHALL use a `useRef` for `selectedSpanId` to prevent stale closure reads. The `handleDeleteSpan` function SHALL be wrapped in `useCallback` with proper dependencies.

#### Scenario: Delete correct span via keyboard
- **WHEN** user selects span A, then selects span B, then presses Delete
- **THEN** span B is deleted (not span A from a stale closure)

### Requirement: Preview primitive uses ref instead of state
The SpanAnnotationManager preview primitive (shown during span drawing on mouse move) SHALL use a `useRef` instead of `useState` to avoid a state/effect feedback loop and unnecessary re-renders.

#### Scenario: Mouse move during drawing does not cause re-render cascade
- **WHEN** the user moves the mouse while drawing a span annotation
- **THEN** the preview primitive updates via ref mutation without triggering a React re-render

### Requirement: Preview primitive cleanup on unmount
The SpanAnnotationManager SHALL detach the preview primitive in the `useEffect` cleanup function when the component unmounts, preventing a leaked canvas primitive.

#### Scenario: Component unmounts during drawing
- **WHEN** the user navigates away while mid-draw
- **THEN** the preview primitive is detached from the chart

### Requirement: fitContent not called on every span change
The SpanAnnotationManager reconciliation effect SHALL NOT call `chart.timeScale().fitContent()` on every span annotation change. `fitContent()` SHALL only be called on initial chart load.

#### Scenario: Span annotation added preserves zoom
- **WHEN** the user adds a new span annotation
- **THEN** the chart maintains the current scroll position and zoom level (no fitContent reset)

### Requirement: Incremental primitive updates
The SpanAnnotationManager SHALL update only the selection state of existing primitives on selection change instead of detaching all and re-attaching all. Full recreation SHALL only occur when the annotation list itself changes (add/remove/edit).

#### Scenario: Selection change is O(1)
- **WHEN** the user clicks a different span annotation
- **THEN** only the previously selected and newly selected primitives are updated (not all N primitives)

#### Scenario: Annotation add triggers full reconciliation
- **WHEN** a new span annotation is added
- **THEN** the primitive list is reconciled (new primitive added, existing ones kept)
