chore: remove stale planning artifacts (#2)

* feat: add flexible studio depth foundations

- add context manifests, engine references, and studio policy gates

- refresh Truthmark 2.2.1 generated surfaces and lane docs

- update OpenSpec tasks and validation coverage

* docs: add Open Game Studio product truth

- add product-capability truth doc for the Codex-native CLI

- cross-link product and engineering truth in route YAML

- update product truth index

* chore: remove stale planning artifacts

---------

Co-authored-by: MerlinH <merlinh221@gmail.com>

engine_reference/unity/plugins.md

@@ -0,0 +1,34 @@
+reviewer: Open Game Studio seed review
+date: 2026-06-14
+source-link: https://docs.unity3d.com/Manual/Packages.html
+
+# Unity Package And Plugin Reference
+
+version-applicability: Unity package manifest, editor tooling, and plugin integrations.
+
+## Prefer
+
+- Keep package changes explicit in `Packages/manifest.json`.
+- Separate editor-only code from runtime assemblies.
+
+## Avoid
+
+- Avoid machine-local package paths unless the task explicitly requires them.
+- Avoid broad editor automation that mutates unrelated assets.
+
+## Pitfalls
+
+- Package resolution can differ across Unity versions.
+- Editor scripts can run during import and produce unexpected asset changes.
+
+## Verification Notes
+
+- Report package manifest diffs and any editor menu or importer smoke check.
+
+## Role Notes
+
+- Tools programmers and engine programmers receive this when package or editor work is relevant.
+
+## Official Links
+
+- https://docs.unity3d.com/Manual/Packages.html