v0.8.5: Extension composability — slots, contributes, lib.require relaxation

Manifest declarations for slots (host surfaces declare injection points)
and contributes (extensions declare UI contributions). lib.require()
relaxed from library-only to any package with exports. Admin slots
aggregation endpoint. SDK renderAll() helper. 7 new tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -2,6 +2,68 @@
 
 All notable changes to Armature are documented here.
 
+## v0.8.5 — Extension Composability
+
+Extensions can now compose with each other through declared slots, UI
+contributions, and cross-package function calls. This is the last kernel
+feature before 1.0 — the platform now supports the "extensions extending
+extensions" pattern.
+
+**Manifest declarations**
+
+- Surfaces declare named `slots` in their manifest (e.g., `toolbar-actions`,
+  `note-footer`) with context documentation for extension authors.
+- Extensions declare `contributes` entries targeting `{host}:{slot}` names
+  (e.g., `notes:toolbar-actions`). Coupling is soft — install order doesn't
+  matter.
+- The kernel validates slot/contribution conventions at install time.
+
+**Backend: `lib.require()` relaxation**
+
+- `lib.require()` now works with any package that declares `exports`, not
+  just `type: "library"` packages. A full package (with surfaces, settings,
+  UI) can export callable functions for cross-package use.
+- The existing `depends` and permission model is unchanged — the called
+  function runs with the target package's permissions.
+
+**Admin slots endpoint**
+
+- `GET /api/v1/admin/slots` returns an aggregated map of all declared slots
+  across installed packages with their contributors.
+- Uninstalling a package that declares slots warns about orphaned
+  contributions in other packages.
+
+**SDK additions**
+
+- `sw.slots.renderAll(name, context)` — convenience helper for host surfaces
+  to render all components in a slot with error isolation.
+- `sw.slots.declare(name, description)` — runtime slot declaration for
+  discoverability and debugging.
+
+**Documentation**
+
+- `PACKAGE-FORMAT.md` — added `slots`, `contributes`, `depends` field docs.
+- `EXTENSION-GUIDE.md` — new "Extension Composability" section with slot
+  naming conventions, contribution patterns, and cross-package call examples.
+- `STARLARK-REFERENCE.md` — updated `lib` module to reflect exports-based
+  calling (not library-type-only).
+
+**Modified files:**
+
+- `server/sandbox/lib_module.go` — type check → exports check
+- `server/handlers/extensions.go` — composability field validation
+- `server/handlers/packages.go` — orphaned contribution warning
+- `server/main.go` — admin slots route registration
+- `src/js/sw/sdk/slots.js` — `renderAll()`, `declare()`, `declarations()`
+- `docs/PACKAGE-FORMAT.md` — slots, contributes, depends
+- `docs/EXTENSION-GUIDE.md` — composability section
+- `docs/STARLARK-REFERENCE.md` — lib module update
+- `docs/DESIGN-extension-composability.md` — status Draft → Implemented
+
+**New files:**
+
+- `server/handlers/admin_slots.go` — admin slot aggregation endpoint
+
 ## v0.8.4 — Documentation Refresh + Surface Sizing Fix
 
 Eight versions of module additions (v0.7.5–v0.8.3) shipped without a