feat(layout): plan 03 — frontend plugin ABI + handshake + load lifecycle

7 files changed, 142 insertions, 6 deletions

diff --git a/src/features/plugins/index.ts b/src/features/plugins/index.ts
index 0f2abbc..7a9d1a0 100644
--- a/src/features/plugins/index.ts
+++ b/src/features/plugins/index.ts
@@ -10,9 +10,12 @@ export type { HighlightSets } from "./logic/highlight";
 export { dependencyHighlightSets } from "./logic/highlight";
 export { isLastProvider, unloadBlockReason } from "./logic/last-provider";
 export { autoCheckBackendPrereqs } from "./logic/prereqs";
-export type { PluginNode, PluginSection } from "./logic/types";
+export type {
+  PluginNode,
+  PluginSection,
+} from "./logic/types";
 export { TIER_ORDER, tierLabel } from "./logic/types";
-export { groupByTier, pluginNodes, splitSections } from "./logic/view-model";
+export { groupByTier, pluginNodes, splitSections, withFrontendStates } from "./logic/view-model";
 export { rowBlockReason, rowChecked, rowSelectable, stateLabel } from "./logic/workspace-row";
 export type { PluginsStore, WorkspacePluginsView } from "./store.svelte";
 export { createPluginsStore } from "./store.svelte";
diff --git a/src/features/plugins/logic/types.ts b/src/features/plugins/logic/types.ts
index 702483b..d5fa4bb 100644
--- a/src/features/plugins/logic/types.ts
+++ b/src/features/plugins/logic/types.ts
@@ -25,6 +25,13 @@ export interface PluginNode {
   readonly dependsOn: readonly string[];
   /** Why the plugin is not loaded (disabled-with-reason) or gone (missing). */
   readonly reason: string | null;
+  /**
+   * The frontend-plugin (plan 03) issue line for the manager row, when the
+   * plugin's FE half is incompatible ("incompatible frontend plugin") or
+   * failed (`frontend failed: <error>`). Absent = the FE half is fine (or
+   * the plugin declares no frontend section).
+   */
+  readonly frontendIssue?: string;
   readonly section: PluginSection;
 }
 
diff --git a/src/features/plugins/logic/view-model.test.ts b/src/features/plugins/logic/view-model.test.ts
index 680ba94..661cade 100644
--- a/src/features/plugins/logic/view-model.test.ts
+++ b/src/features/plugins/logic/view-model.test.ts
@@ -1,7 +1,7 @@
 import type { PluginListResponse, PluginTier } from "@dispatch/transport-contract";
 import { describe, expect, it } from "vitest";
 import { emptyListResponse, node } from "./test-fixtures";
-import { groupByTier, pluginNodes, splitSections } from "./view-model";
+import { groupByTier, pluginNodes, splitSections, withFrontendStates } from "./view-model";
 
 function listResponse(overrides: Partial<PluginListResponse> = {}): PluginListResponse {
   return {
@@ -225,3 +225,72 @@ describe("splitSections", () => {
     expect(sections.missing.map((n) => n.id)).toEqual(["gone"]);
   });
 });
+
+// ── withFrontendStates (plan 03) — the manager rows' FE-half issues ─────────
+
+describe("withFrontendStates", () => {
+  function listWith(...ids: readonly string[]): PluginListResponse {
+    return {
+      loaded: ids.map((id) => ({
+        id,
+        name: id,
+        version: "1.0.0",
+        tier: "standard" as const,
+        trust: "local" as const,
+        locked: false,
+        dependsOn: [],
+      })),
+      disabledWithReason: [],
+      discovered: [],
+      missing: [],
+    };
+  }
+
+  it("renders the plan-mandated grammar for an incompatible FE half", () => {
+    const nodes = pluginNodes(listWith("bad"));
+    const states = new Map([["bad", { kind: "incompatible", apiVersion: "^2" } as const]]);
+    const out = withFrontendStates(nodes, states);
+    expect(out[0]?.frontendIssue).toBe("incompatible frontend plugin");
+  });
+
+  it("renders the activation error for a failed FE half", () => {
+    const nodes = pluginNodes(listWith("broken"));
+    const states = new Map([["broken", { kind: "failed", error: "boom" } as const]]);
+    const out = withFrontendStates(nodes, states);
+    expect(out[0]?.frontendIssue).toBe("frontend failed: boom");
+  });
+
+  it("a loaded FE half adds no issue line; absent states add none", () => {
+    const nodes = pluginNodes(listWith("ok", "no-fe"));
+    const states = new Map([["ok", { kind: "loaded" } as const]]);
+    const out = withFrontendStates(nodes, states);
+    expect(out.find((n) => n.id === "ok")?.frontendIssue).toBeUndefined();
+    expect(out.find((n) => n.id === "no-fe")?.frontendIssue).toBeUndefined();
+  });
+
+  it("never annotates non-loaded sections (discovered / missing rows)", () => {
+    const response: PluginListResponse = {
+      loaded: [],
+      disabledWithReason: [],
+      discovered: [
+        {
+          id: "dis",
+          name: "dis",
+          version: "1.0.0",
+          tier: "standard",
+          trust: "local",
+          dir: "/plugins/dis",
+        },
+      ],
+      missing: [],
+    };
+    const states = new Map([["dis", { kind: "failed", error: "boom" } as const]]);
+    const out = withFrontendStates(pluginNodes(response), states);
+    expect(out[0]?.frontendIssue).toBeUndefined();
+  });
+
+  it("an empty state map is the identity (no allocation on the hot path)", () => {
+    const nodes = pluginNodes(listWith("a"));
+    expect(withFrontendStates(nodes, new Map())).toBe(nodes);
+  });
+});
diff --git a/src/features/plugins/logic/view-model.ts b/src/features/plugins/logic/view-model.ts
index 20d7d68..5a66ffa 100644
--- a/src/features/plugins/logic/view-model.ts
+++ b/src/features/plugins/logic/view-model.ts
@@ -1,4 +1,5 @@
 import type { PluginListResponse } from "@dispatch/transport-contract";
+import type { FrontendPluginState } from "../../../core/plugin-abi";
 import { normalizeTier, type PluginNode, type PluginSection, TIER_ORDER } from "./types";
 
 /**
@@ -79,6 +80,34 @@ export function pluginNodes(response: PluginListResponse): readonly PluginNode[]
 }
 
 /**
+ * Merge the frontend-plugin (plan 03) per-plugin FE states into the node
+ * list — the manager rows' `frontendIssue` line. Pure input → output:
+ * - `incompatible` → the plan-mandated "incompatible frontend plugin"
+ *   grammar (the backend apiVersion-mismatch wording, FE half);
+ * - `failed` → the activation error (the FE half failed; the backend half
+ *   stays loaded).
+ * Loaded rows only — the FE states never apply to discovered/missing rows.
+ */
+export function withFrontendStates(
+  nodes: readonly PluginNode[],
+  states: ReadonlyMap<string, FrontendPluginState>,
+): readonly PluginNode[] {
+  if (states.size === 0) return nodes;
+  return nodes.map((node) => {
+    if (node.section !== "loaded") return node;
+    const state = states.get(node.id);
+    if (state === undefined) return node;
+    const issue =
+      state.kind === "incompatible"
+        ? "incompatible frontend plugin"
+        : state.kind === "failed"
+          ? `frontend failed: ${state.error}`
+          : null;
+    return issue === null ? node : { ...node, frontendIssue: issue };
+  });
+}
+
+/**
  * Cluster nodes for one manager table: tier groups in display order (Core →
  * Providers → Standard), each tier's rows sorted by id. Tiers with no rows
  * are omitted. Used by the loaded table's tier grouping (plan 07 §7.2).
diff --git a/src/features/plugins/store.svelte.ts b/src/features/plugins/store.svelte.ts
index 580293e..fe48940 100644
--- a/src/features/plugins/store.svelte.ts
+++ b/src/features/plugins/store.svelte.ts
@@ -3,6 +3,7 @@ import type {
   SetWorkspacePluginStateRequest,
   WorkspacePluginRow,
 } from "@dispatch/transport-contract";
+import type { FrontendPluginState } from "../../core/plugin-abi";
 import type { PluginOpResult, PluginScanResult, PluginsHttp } from "./adapter/http";
 import type { PluginNode } from "./logic/types";
 import { pluginNodes } from "./logic/view-model";
@@ -70,6 +71,16 @@ export interface PluginsStore {
    * connected client converges. Fire-and-forget.
    */
   onExtensionsChanged(): void;
+
+  /**
+   * The frontend-plugin (plan 03) per-plugin FE states — reported by the
+   * plugin host after every driver sync. Rendered by the manager rows:
+   * `incompatible` → "incompatible frontend plugin" (the backend-mismatch
+   * grammar), `failed` → the activation error. Absent = no FE section.
+   */
+  readonly frontendStates: ReadonlyMap<string, FrontendPluginState>;
+  /** The plugin host's post-sync report (the only writer). */
+  setFrontendStates(states: ReadonlyMap<string, FrontendPluginState>): void;
 }
 
 /** One open workspace modal's view (rows + materialized provider count). */
@@ -86,6 +97,7 @@ export function createPluginsStore(http: PluginsHttp): PluginsStore {
   let error = $state<string | null>(null);
   let lastScan = $state<PluginScanResult | null>(null);
   let workspaceView = $state<WorkspacePluginsView | null>(null);
+  let frontendStates = $state<ReadonlyMap<string, FrontendPluginState>>(new Map());
 
   // Normalized nodes — derived so the graph logic re-runs only when the list
   // changes, not on every read.
@@ -194,5 +206,13 @@ export function createPluginsStore(http: PluginsHttp): PluginsStore {
       const open = workspaceView?.workspaceId;
       if (open !== undefined) void this.openWorkspace(open);
     },
+
+    get frontendStates(): ReadonlyMap<string, FrontendPluginState> {
+      return frontendStates;
+    },
+
+    setFrontendStates(states: ReadonlyMap<string, FrontendPluginState>): void {
+      frontendStates = states;
+    },
   };
 }
diff --git a/src/features/plugins/ui/PluginManager.svelte b/src/features/plugins/ui/PluginManager.svelte
index cd3d542..fd2a8a7 100644
--- a/src/features/plugins/ui/PluginManager.svelte
+++ b/src/features/plugins/ui/PluginManager.svelte
@@ -6,7 +6,7 @@
   import { autoCheckBackendPrereqs } from "../logic/prereqs";
   import { dependencyHighlightSets } from "../logic/highlight";
   import { unloadBlockReason } from "../logic/last-provider";
-  import { splitSections } from "../logic/view-model";
+  import { splitSections, withFrontendStates } from "../logic/view-model";
   import PluginTable from "./PluginTable.svelte";
   import UnloadConfirmModal from "./UnloadConfirmModal.svelte";
 
@@ -17,9 +17,13 @@
   });
 
   // ── Derived sections + hover highlighting (§8) ────────────────────────────
-  const sections = $derived(splitSections(plugins.nodes));
+  // The FE-half states (plan 03) merge into the nodes here — one reactive
+  // derivation over both inputs (the normalized nodes + the plugin host's
+  // post-sync state map).
+  const nodes = $derived(withFrontendStates(plugins.nodes, plugins.frontendStates));
+  const sections = $derived(splitSections(nodes));
   let hoveredId = $state<string | null>(null);
-  const highlight = $derived(dependencyHighlightSets(hoveredId, plugins.nodes));
+  const highlight = $derived(dependencyHighlightSets(hoveredId, nodes));
 
   function highlightFor(id: string): "dep" | "dependent" | null {
     if (highlight.deps.has(id)) return "dep";
diff --git a/src/features/plugins/ui/PluginRow.svelte b/src/features/plugins/ui/PluginRow.svelte
index 457bd29..73e0b18 100644
--- a/src/features/plugins/ui/PluginRow.svelte
+++ b/src/features/plugins/ui/PluginRow.svelte
@@ -83,6 +83,10 @@
       {#if node.reason !== null}
         <span class="text-xs text-error">{node.reason}</span>
       {/if}
+      {#if node.frontendIssue !== undefined}
+        <!-- plan 03: the FE half's state — "incompatible frontend plugin" or the activation error -->
+        <span class="text-xs text-error">{node.frontendIssue}</span>
+      {/if}
       {#if node.dependsOn.length > 0}
         <span class="text-xs opacity-60">depends on: {node.dependsOn.join(", ")}</span>
       {/if}