docs(work): map testing and editor northstars

Add repo-local northstars and ready slices for testing strategy, LSP/editor completion, and hemplate highlighting boundaries.

work/slices/SLICE-0008-cross-file-build-facts.md

@@ -0,0 +1,41 @@
+---
+id: SLICE-0008
+type: slice
+status: ready
+parent: NS-0002
+title: Surface cross-file facts without replacing build validation
+refs:
+  - REQUIREMENTS.md
+  - docs/editor-support.md
+  - docs/diagnostics.md
+  - hemx-build/src/lib.rs
+  - hemx-lsp/src/main.rs
+---
+
+## Objective
+
+Define and prove the handoff between editor-visible template facts and `cargo check`/`hemx-build` completeness checks for template/handler references.
+
+## Authority
+
+`REQUIREMENTS.md` `check/001`, `check/003`, `diagnostics/004`, and `diagnostics/005` require cross-file references visible to build validation to fail at `cargo check` with useful spans, while editor overlays remain optional glue.
+
+## Close when
+
+- A test fixture demonstrates a template/handler reference that editor diagnostics can surface and `cargo check`/build validation also rejects.
+- The LSP path reports useful spans without becoming the global source of truth.
+- Global completeness boundaries remain component-scoped unless mount/tests are needed.
+
+## Verification
+
+- `cargo test -p hemx-lsp`
+- `cargo check --workspace` or a focused compile-fail/build fixture when build validation changes.
+
+## Non-goals
+
+- Do not make the LSP own Rust type checking.
+- Do not create a persistent project index unless a later slice proves it is required.
+
+## Evidence
+
+`docs/diagnostics.md` and `hemx-build` diagnostics define the authority boundary that editor support must reflect.