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dev-docs/reference/LEARNINGS.md

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+# OpenNoodl Development Learnings
+
+This document records discoveries, gotchas, and non-obvious patterns found while working on OpenNoodl. Search this file before tackling complex problems.
+
+---
+
+## Project Migration & Versioning
+
+### [2025-07-12] - Legacy Projects Are Already at Version 4
+
+**Context**: Investigating what migration work is needed for legacy Noodl v1.1.0 projects.
+
+**Discovery**: Legacy projects from Noodl v1.1.0 are already at project format version "4", which is the current version expected by the editor. This significantly reduces migration scope.
+
+**Location**: 
+- `packages/noodl-editor/src/editor/src/models/projectmodel.ts` - Contains `Upgraders` object for format 0→1→2→3→4
+- `packages/noodl-editor/src/editor/src/models/ProjectPatches/` - Node-level patches (e.g., `RouterNavigate`)
+
+**Key Points**:
+- Project format version is stored in `project.json` as `"version": "4"`
+- The existing `ProjectPatches/` system handles node-level migrations automatically on load
+- No major version migration infrastructure is needed for v1.1.0→v2.0.0
+- The `Upgraders` object has handlers for versions 0-4, upgrading sequentially
+
+**Keywords**: project migration, version upgrade, legacy project, project.json, upgraders
+
+---
+
+### [2025-07-12] - @noodl/platform FileInfo Interface
+
+**Context**: Writing utility functions that use `filesystem.listDirectory()`.
+
+**Discovery**: The `listDirectory()` function returns `FileInfo[]`, not strings. Each FileInfo has:
+- `name: string` - Just the filename
+- `fullPath: string` - Complete path
+- `isDirectory: boolean`
+
+**Location**: `packages/noodl-platform/src/filesystem/IFilesystem.ts`
+
+**Keywords**: filesystem, listDirectory, FileInfo, platform API
+
+---
+
+## Template for Future Entries
+
+```markdown
+### [YYYY-MM-DD] - Brief Title
+
+**Context**: What were you trying to do?
+
+**Discovery**: What did you learn?
+
+**Location**: What files/areas does this apply to?
+
+**Keywords**: [searchable terms]
+```