Initial TrueGrowth source import

openspec/changes/update-canvas-batch-flow-layout/specs/canvas-insertion/spec.md

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+## ADDED Requirements
+
+### Requirement: Batch canvas insertion uses viewport flow layout
+
+Batch canvas insertion SHALL place inserted items left-to-right using the current canvas viewport width in canvas coordinates, then wrap to a new row when the next item would exceed that width.
+
+For media items inserted through the batch path, the final insertion size SHALL remain stable for the batch flow and SHALL NOT be rewritten after load in a way that changes the batch spacing.
+
+#### Scenario: Wide viewport fits multiple items on one row
+- **GIVEN** the current canvas viewport can fit multiple batch items at the active zoom
+- **WHEN** a batch insertion runs
+- **THEN** items SHALL be inserted left-to-right on the same row until the next item would exceed the viewport width
+
+#### Scenario: Narrow or zoomed-in viewport wraps items
+- **GIVEN** the current canvas viewport cannot fit the next batch item at the active zoom
+- **WHEN** a batch insertion runs
+- **THEN** the next item SHALL be inserted at the batch start x coordinate on the next row
+- **AND** the next row SHALL start after the tallest item in the previous row plus the configured vertical gap
+
+#### Scenario: Batch insertion scrolls to the batch center
+- **GIVEN** one or more items were inserted by a batch insertion
+- **WHEN** insertion completes
+- **THEN** the canvas SHALL scroll toward the center of the inserted batch bounds
+
+#### Scenario: Batch media sizes stay stable
+- **GIVEN** image or video items are inserted through the batch flow
+- **WHEN** the media finishes loading
+- **THEN** the batch spacing SHALL remain based on the original batch layout size
+- **AND** later media resizing SHALL NOT shift the row spacing for the completed batch