feat: milestones 6b-fix through 6e — default-editor, files plugin, workspace host, workspaceItems contribution

- Fix PluginCard openProviders display
- Add default-editor plugin (text/markdown/notes-context)
- Add files plugin with workspaceItems placement
- Add workspaceItems contribution point (Go + API + mock + SDK)
- Add WorkspaceHost component for workspace area
- WorkspaceTree dispatches selection event
- Fix default-editor layout to fill container
- Fix PluginCard unsafe .length access
- Add E2E tests: 34/34 pass
- Add bundle execution check to official-plugins check.sh
- Update docs: PLUGIN_RUNTIME, DEV_PLUGINS, MILESTONE_6B/6C/6D plans

docs/DEV_PLUGINS.md

@@ -101,6 +101,12 @@ Workbench selects by resource kind, extension/mime, context (`generic-text`,
 deterministic `pluginId/providerId` tie-break. If nothing matches, Workbench
 shows `no-provider` fallback instead of a core editor.
 
+The official `verstak.default-editor` plugin provides three openProviders:
+`verstak.default-editor.text` (generic-text), `verstak.default-editor.markdown`
+(generic-markdown), and `verstak.default-editor.notes-markdown` (notes-context).
+It uses a single unified `DefaultEditor` component with textarea-based editing,
+simple markdown preview, dirty state tracking, and Ctrl+S save.
+
 This is a cooperative contract, not a sandbox. Bundled plugins run in the same JS
 context as the desktop frontend; real isolation is deferred to the sidecar/sandbox
 milestone.

docs/MILESTONE_6B_PLAN.md

@@ -133,3 +133,16 @@ Out of scope:
 - Watcher/sync/binary streaming/external editor.
 - Sidecar/security boundary.
 - Large rewrite.
+
+## 6b-fix: Infrastructure Gaps Closed
+
+Post-review fixes before Milestone 6c:
+
+- Added `openProviders` to `verstak-sdk/schemas/contributions.json` contribution points.
+- Added provider matching tests: text/markdown preference, MIME matching, extension
+  case-insensitivity, multiple supports entries, kind mismatch.
+- Added disabled provider exclusion test in `api/app_test.go`.
+- Fixed SDK `build.sh`/`test.sh` to detect incomplete `node_modules`.
+- Documented disabled provider lifecycle: contributions remain in registry until
+  ReloadPlugins; `activeOpenProviders()` filters disabled/unloaded at request time.
+- Installed Playwright browsers for E2E tests.

docs/MILESTONE_6C_DEFAULT_EDITOR_PLAN.md

@@ -0,0 +1,65 @@
+# Milestone 6c — Default Editor Plugin
+
+## Goal
+
+Create the official Default Editor Plugin as an openProvider for text, generic
+markdown, and notes-context markdown files. Core desktop does not own or import
+the editor component.
+
+## What was built
+
+### Plugin: `verstak.default-editor`
+
+Location: `verstak-official-plugins/plugins/default-editor/`
+
+**Manifest declares 3 openProviders:**
+
+| Provider ID | Context | Extensions |
+|-------------|---------|------------|
+| `verstak.default-editor.text` | `generic-text` | `.txt`, `.log`, `.conf`, `.ini`, `.toml`, `.yaml`, `.yml`, `.json`, `.csv` |
+| `verstak.default-editor.markdown` | `generic-markdown` | `.md`, `.markdown` |
+| `verstak.default-editor.notes-markdown` | `notes-markdown` | `.md`, `.markdown` |
+
+All providers use the same `DefaultEditor` component (unified, not 3 separate editors).
+
+**Permissions:** `files.read`, `files.write`, `workbench.open`
+
+**Capabilities required:** `verstak/core/files/v1`, `verstak/core/workbench/v1`
+
+### Frontend component: `DefaultEditor`
+
+- **Modes:** text (textarea), generic-markdown (editor + preview), notes-markdown (editor + preview + notes badge)
+- **File loading:** `api.files.readText(path)` with loading/error states
+- **Saving:** `api.files.writeText(path, content, { overwrite: true })` with dirty/saved/error states
+- **Keyboard:** Ctrl+S / Cmd+S save, Tab indentation
+- **Markdown preview:** Simple renderer (no raw HTML, no script injection)
+- **Notes context:** Badge + info bar, no separate note entity, no `.verstak/notes`
+
+## Verification
+
+- `go test ./...` — PASS
+- `go vet ./...` — PASS
+- `npm run build` (frontend) — PASS
+- `npm run test:e2e` — 28/28 PASS (20 existing + 8 new)
+- `scripts/check.sh` (official-plugins) — PASS
+- `scripts/build.sh` (official-plugins) — PASS
+- SDK checks — PASS
+
+## Manual testing
+
+Until Files UI plugin exists, use platform-test diagnostics panel to manually
+open files via workbench: click "Open Text Diagnostic", "Open Markdown Diagnostic",
+or "Open Notes Diagnostic" buttons. These call `api.workbench.editResource` and
+route through the default-editor provider.
+
+## Deferred
+
+- CodeMirror/Monaco editor
+- Backlinks, internal link navigation
+- Secret widgets
+- Image asset pipeline
+- Files UI plugin
+- Notes UI plugin
+- Watcher/sync
+- External open
+- Sidecar/security isolation

docs/MILESTONE_6D_FILES_PLUGIN_PLAN.md

@@ -0,0 +1,64 @@
+# Milestone 6d — Minimal Files Plugin
+
+## Goal
+
+Create a minimal Files plugin that shows vault files/folders and opens files
+through Workbench openResource. No editor embedded.
+
+## What was built
+
+### Plugin: `verstak.files`
+
+Location: `verstak-official-plugins/plugins/files/`
+
+**Contributions:**
+- views: `verstak.files.view` → `FilesView` component
+- No sidebarItems — Files is not a global sidebar item
+
+**Permissions:** `files.read`, `files.write`, `workbench.open`, `ui.register`
+
+### Files View
+
+- Root listing on mount
+- Folder navigation (double-click)
+- File open via `api.workbench.openResource()`
+- Breadcrumb navigation
+- Create folder/file buttons
+- Refresh button
+- Loading/error/empty states
+- `.verstak` filtered out
+
+### Provider priority
+
+- default-editor: priority 50
+- platform-test diagnostic: priority 10
+- default-editor wins for normal file opens
+
+### Bundle fix
+
+Fixed missing opening quote in STYLES string (`.files-empty` → `'.files-empty'`).
+Added automated bundle execution check to `scripts/check.sh`.
+
+## 6d-hotfix
+
+- Removed sidebarItems from Files plugin (Files is not a global sidebar item)
+- Added `[frontend bundle execution]` check to `check.sh` — verifies all plugin
+  bundles parse via `new Function()` and register via `VerstakPluginRegister`
+- Updated E2E tests: Files no longer expected in global sidebar
+- Documented: sidebarItems are global shell navigation, not workspace template tabs
+
+## Verification
+
+- `go test ./...` — PASS
+- `go vet ./...` — PASS
+- `npm run build` — PASS
+- `npm run test:e2e` — 34/34 PASS
+- Official plugins — 3 plugins built, bundle execution check passes
+- SDK — 11/11 tests pass
+
+## Deferred
+
+- Notes plugin, rename/move/trash UI, drag-and-drop, context menu,
+  watcher/inotify, sync, external open, binary streaming, sidecar/security,
+  workspace template host (Milestone 6d2)
+

docs/PLUGIN_RUNTIME.md

@@ -335,10 +335,27 @@ extension/mime, context, user preference, priority, then deterministic
 `pluginId/providerId` fallback. If nothing matches, Workbench returns
 `status: "no-provider"` and shows the fallback view instead of a core editor.
 
+Disabled/failed/missing-required-capability plugins are excluded from provider
+selection at request time by `activeOpenProviders()`. Their contributions may
+remain in the registry until the next `ReloadPlugins()` cycle, but they never
+match during routing.
+
 Draft app-global preferences are `defaultTextEditorProvider`,
 `defaultMarkdownEditorProvider`, and `defaultNotesMarkdownEditorProvider`.
 Vault-scoped and per-extension overrides are deferred.
 
+### Default Editor Plugin
+
+The official `verstak.default-editor` plugin (`verstak-official-plugins/plugins/default-editor/`)
+provides openProviders for text, generic markdown, and notes-context markdown files.
+It uses `api.files.readText` / `api.files.writeText` for file I/O and mounts through
+the standard `PluginBundleHost` / provider host mechanism. Core does not import or
+reference this plugin directly.
+
+Provider plugins may have no sidebar item — openProviders are contribution points
+for workbench routing, not navigation. Plugin Manager displays openProviders in the
+contributions summary.
+
 ### API methods
 
 `settings`