Add canonical repository structure instructions

Author: ToolboxAid

docs_build/dev/ProjectInstructions/README.txt

@@ -40,3 +40,6 @@ READ THIS FIRST
 9. Follow OWNER governance decisions.
 10. When guidance conflicts, newest OWNER-approved guidance wins.
 11. Batch Governance Mode is the default for governance, documentation, and administrative work.
+
+Addendum index:
+- Canonical Repository Structure: project-instructions/addendums/canonical-repository-structure.md

project-instructions/addendums/canonical-repository-structure.md

@@ -0,0 +1,78 @@
+# Canonical Repository Structure
+
+## Purpose
+
+Prevent technical debt by requiring all new and modified code to follow one repository structure.
+
+## Canonical Structure
+
+Tools:
+- toolbox/{tool-name}/index.html
+
+Tool assets:
+- assets/toolbox/{tool-name}/js/index.js
+- assets/toolbox/{tool-name}/css/index.css
+
+Themes:
+- assets/theme-v1/
+- assets/theme-v2/
+
+Shared JavaScript:
+- assets/js/shared/
+
+Engine:
+- src/engine/{feature-name}/
+
+API:
+- api/{feature-name}/
+
+Server:
+- server/{feature-name}/
+
+Tests:
+- tests/toolbox/{tool-name}/
+- tests/engine/{feature-name}/
+- tests/api/{feature-name}/
+- tests/server/{feature-name}/
+- tests/js/shared/
+- tests/regression/
+
+## Rules
+
+- Theme first. Use theme styles whenever possible.
+- Tool CSS is allowed only when a requirement cannot be satisfied by the active theme.
+- Every tool must be independently testable.
+- Regression tests do not replace tool-level tests.
+- Shared functionality belongs in assets/js/shared/.
+- New development must follow the canonical structure.
+- No new scattered JavaScript folders.
+- No new scattered CSS folders.
+- No new scattered test folders.
+
+## Legacy Migration
+
+When a tool is modified:
+
+1. Review JS location.
+2. Review CSS location.
+3. Review test location.
+4. Move touched files into the canonical structure.
+5. Update imports.
+6. Update tests.
+7. Remove legacy references.
+
+Legacy files may only be deleted when no active references remain.
+
+## Folder Ownership
+
+A folder may contain only assets related to that feature.
+
+Example:
+
+assets/toolbox/text-to-speech/
+
+may not contain files used exclusively by another tool.
+
+Shared functionality must be moved to:
+
+assets/js/shared/