feat: add plugin system with grpc runtime and native ui plugins (#1742)

* feat: add plugin system with grpc runtime and native ui plugins

- go plugin backends ship as release tarballs (per-platform binaries, checksums) that
  kandev installs from url/upload or filesystem sideload+sync, then spawns and
  supervises via hashicorp/go-plugin (unix socket / loopback tcp+automtls)
- strict typed grpc contract (kandev.plugin.v1): DeliverEvent/InvokeTool/HandleWebhook
  plus a capability-gated host service (state, secrets, emit); author sdk in
  pkg/pluginsdk; packaging cli in cmd/plugin-pack
- native frontend bundles: window.registerKandevPlugin + registry/host loader with
  dynamic routes, nav items, slots and ws handlers; plugins settings page with
  install dialog, sync button and enable/disable/uninstall
- gated behind the plugins feature flag (prod off, dev/e2e on); covered by unit and
  integration tests plus playwright e2e against a real packaged fixture plugin

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(plugins): hydrate base app context on plugin routes

Plugin-owned SPA routes classify as RouteUnknown, so the boot payload shipped
only feature flags — no workspaces, workflows, or kanban context. Native plugin
UI (e.g. host.ui.TaskCreateDialog) then had an empty store. Hydrate the same
base context as the Home route for unknown SPA routes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* feat(plugins): expose TaskCreateDialog on host.ui

Lets a native plugin open kandev's real create-task modal (prefilled via
initialValues) instead of POSTing directly.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(plugins): harden filesystem/URL sinks against CodeQL findings

Add sink-level guards on the plugin trust boundary: securejoin containment on
archive extraction (zip-slip), plugin-id validation before every fs_store path,
http/https scheme validation on install-from-URL, and non-interpolated ws-handler
error logging.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(plugins): address review findings (races, resource caps, lifecycle)

- serialize per-plugin startup to close a TOCTOU double-spawn race, and let a
  plugin restart after exhausting attempts
- bound plugin startup with an explicit 30s timeout
- reject backslash paths and cap decompressed bytes by actual size in pkgtar;
  only mark a package Signed when a verifier actually ran and passed
- delete plugin_state on uninstall; validate webhook keys against the manifest
  and cap webhook body size; restart an active plugin when a new version installs

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(plugins): sanitize plugin-id path sinks for CodeQL

Pin the plugin id to a single path segment with filepath.Base at recordPath/
configPath and pkgtar.Remove — a barrier the taint analysis recognizes.
Behaviour-identical for valid ids (already validated by safePluginID); clears
the go/path-injection alerts.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(plugins): inline plugin-id validation at path sinks for CodeQL

filepath.Base does not strip '..', so it is not a path-injection barrier. Call
the recognized safePluginID / id-pattern guard inline in Delete/GetConfig/
SetConfig and pkgtar.Remove — the same barrier that already cleared the Get sink.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(plugins): address code-review findings (backend)

- add capability-gating tests for the Host RPC service (was untested)
- close a stop-during-start orphan race so Disable/Uninstall can't leave a
  supervised subprocess behind
- on failed upgrade, remove only the new version dir (not all versions + data);
  restart the prior version
- validate manifest version and reject ids ending in .config (record-file alias)
- make Deliverer.Refresh non-blocking and cancel in-flight delivery on worker stop
- clamp out-of-range webhook status, skip-and-warn corrupt records in List,
  write records atomically, semver-aware sideload version pick

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(plugins): address code-review findings (frontend)

- wrap plugin routes + settings routes in a shared PluginErrorBoundary so a
  throwing plugin page shows a fallback instead of white-screening the SPA
- fix disable/re-enable in one session: keep the cached registration and
  re-run initialize instead of relying on a cached ES-module re-import
- prefix root-relative bundle/style URLs with apiBaseUrl (split-origin/Tauri)
- surface partial-install warnings via toast.warning instead of a bare success
- dedupe/remove injected style links on unload; gate PluginNavItems on the flag

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(plugins): serialize per-plugin lifecycle + guard config writes

- add a per-plugin keyed lock in Service so concurrent Enable/Disable/Install/
  Uninstall/UpdateConfig for one id are serialized (no status-machine race)
- take s.mu in SetConfig/GetConfig and write config atomically
- bound each plugin initialize() with a timeout so one hung bundle can't stall
  the rest of the boot load

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* test(plugins): split service_test.go to satisfy file-length lint

Move the install/URL test group into service_install_test.go; no logic change.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* ci: build and ship the e2e fixture plugin package to E2E shards

The plugin E2E specs' global-setup requires apps/backend/.build/kandev-plugin-e2e-1.0.0.tar.gz.
Build it in the E2E build job, upload it as an artifact, and download it in both
the regular and container shard jobs.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Kandev Agent <agent@kandev.dev>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Makefile

@@ -331,6 +331,15 @@ build-backend-quiet:
 	@printf "  $(DIM)Backend$(RESET)\n"
 	@$(MAKE) -s -C $(BACKEND_DIR) build >/dev/null 2>&1
 
+## Package the plugin-fixture SDK plugin used by tests/plugins/plugins.spec.ts.
+## e2e/global-setup.ts checks the resulting tar.gz exists (like it does for
+## the kandev/mock-agent binaries) but does not build it itself — this target
+## is the "make it exist" step, wired into test-e2e* below.
+.PHONY: build-e2e-plugin-package
+build-e2e-plugin-package:
+	@printf "$(CYAN)Packaging e2e fixture plugin...$(RESET)\n"
+	@$(MAKE) -C $(BACKEND_DIR) e2e-plugin-package
+
 .PHONY: build-web
 build-web:
 	@printf "$(CYAN)Building web app...$(RESET)\n"
@@ -430,17 +439,17 @@ test-scripts:
 	@node --test scripts/validate-public-docs.test.mjs
 
 .PHONY: test-e2e
-test-e2e: build-backend build-web
+test-e2e: build-backend build-web build-e2e-plugin-package
 	@printf "$(CYAN)Running E2E tests (headless, parallel)...$(RESET)\n"
 	@cd $(APPS_DIR) && $(PNPM) --filter @kandev/web e2e
 
 .PHONY: test-e2e-headed
-test-e2e-headed: build-backend build-web
+test-e2e-headed: build-backend build-web build-e2e-plugin-package
 	@printf "$(CYAN)Running E2E tests (headed)...$(RESET)\n"
 	@cd $(APPS_DIR) && $(PNPM) --filter @kandev/web e2e:headed
 
 .PHONY: test-e2e-ui
-test-e2e-ui: build-backend build-web
+test-e2e-ui: build-backend build-web build-e2e-plugin-package
 	@printf "$(CYAN)Opening Playwright UI mode...$(RESET)\n"
 	@cd $(APPS_DIR) && $(PNPM) --filter @kandev/web e2e:ui