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-0005-lsp-diagnostics-parity.md

@@ -0,0 +1,43 @@
+---
+id: SLICE-0005
+type: slice
+status: ready
+parent: NS-0002
+title: Prove LSP diagnostics parity with hemx-build
+refs:
+  - REQUIREMENTS.md
+  - docs/diagnostics.md
+  - docs/editor-support.md
+  - hemx-lsp/src/main.rs
+  - hemx-build/src/lib.rs
+---
+
+## Objective
+
+Make LSP diagnostics a faithful editor transport for `hemx-build` diagnostics across open, change, save, close, and CLI file checks.
+
+## Authority
+
+`docs/diagnostics.md` and `REQUIREMENTS.md` `diagnostics/004`, `diagnostics/005`, and `check/001` require editor overlays to share compiler authority and preserve useful spans.
+
+## Close when
+
+- A focused LSP test opens an invalid `.heml` document and observes the same diagnostic code/severity/range as the `hemx-lsp diagnostics FILE.heml` path.
+- `didChange` updates diagnostics from in-memory text.
+- `didSave` with and without text uses the documented source of truth.
+- `didClose` clears diagnostics.
+
+## Verification
+
+- `cargo test -p hemx-lsp`
+- `cargo run -p hemx-lsp -- diagnostics <fixture>.heml`
+- `cargo check --workspace` if public LSP/build types change.
+
+## Non-goals
+
+- Do not implement a second `.heml` parser in the LSP.
+- Do not add provider-specific VS Code/Neovim behavior in this slice.
+
+## Evidence
+
+`hemx-lsp/src/main.rs` already has diagnostics CLI and LSP publish paths that can be covered with protocol tests.