feat: add workspace agents for reusable agent definitions across patterns

Introduce a workspace-level agent library that allows users to define
agents once and reference them from multiple orchestration patterns.

Domain model:
- Add WorkspaceAgentDefinition type with name, model, instructions, etc.
- Extend PatternAgentDefinition with optional workspaceAgentId and overrides
- Add resolution helpers that merge workspace agent base with per-pattern overrides
- Extend WorkspaceSettings with agents array and normalize on load

IPC & main process:
- Add saveWorkspaceAgent/deleteWorkspaceAgent IPC channels and handlers
- Resolve workspace agent references in buildEffectivePattern before
  sending to sidecar (no C# changes needed)

Settings UI:
- Add 'Agents' tab under Orchestration in the Settings panel
- Create WorkspaceAgentEditor component using ToolingEditorShell
- Show usage count (which patterns reference each agent)

Pattern editor integration:
- Add agent picker dropdown: 'New inline agent' or 'From library'
- Show linked badge (chain icon) on referenced agent graph nodes
- Show linked workspace agent banner in the inspector
- Add 'Save to Agent Library' action to promote inline agents
- Add 'Unlink' action to convert referenced agents back to inline

Tests:
- Add unit tests for resolution helpers (resolvePatternAgent,
  resolvePatternAgents, findWorkspaceAgentUsages, normalize)
- Update existing tooling test for new agents field

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/renderer/components/pattern-graph/GraphNodes.tsx

@@ -1,6 +1,6 @@
 import { memo } from 'react';
 import { Handle, Position, type NodeProps } from '@xyflow/react';
-import { CircleUser, Shuffle, Layers, Radio, Bot } from 'lucide-react';
+import { CircleUser, Link2, Shuffle, Layers, Radio, Bot } from 'lucide-react';
 
 import type { GraphNodeData } from '@renderer/lib/patternGraph';
 import type { PatternGraphNodeKind } from '@shared/domain/pattern';
@@ -56,6 +56,11 @@ function GraphNodeContent({ data, selected }: { data: GraphNodeData; selected: b
           SYS
         </span>
       )}
+      {data.isLinked && (
+        <span className="ml-1 flex size-4 items-center justify-center rounded bg-[var(--color-accent)]/15" title="Linked workspace agent">
+          <Link2 className="size-2.5 text-[var(--color-accent)]" />
+        </span>
+      )}
     </div>
   );
 }

src/renderer/components/pattern-graph/PatternGraphInspector.tsx

@@ -1,4 +1,4 @@
-import { Bot, ChevronDown, ChevronUp, CircleUser, Layers, Radio, Shuffle, Trash2 } from 'lucide-react';
+import { Bot, ChevronDown, ChevronUp, CircleUser, Layers, Library, Link2, Radio, Shuffle, Trash2, Unlink } from 'lucide-react';
 
 import {
   findModel,
@@ -12,6 +12,7 @@ import type {
   PatternGraph,
   PatternGraphNodeKind,
 } from '@shared/domain/pattern';
+import type { WorkspaceAgentDefinition } from '@shared/domain/workspaceAgent';
 import {
   canMoveSequential,
   findAgentForNode,
@@ -25,8 +26,11 @@ interface PatternGraphInspectorProps {
   graph: PatternGraph;
   mode: OrchestrationMode;
   selectedNodeId: string | null;
+  workspaceAgents: WorkspaceAgentDefinition[];
   onAgentChange: (agentId: string, patch: Partial<PatternAgentDefinition>) => void;
   onAgentRemove: (agentId: string) => void;
+  onAgentPromote: (agentId: string) => void;
+  onAgentUnlink: (agentId: string) => void;
   onGraphChange: (graph: PatternGraph) => void;
 }
 
@@ -118,8 +122,11 @@ function AgentNodeInspector({
   mode,
   graph,
   nodeId,
+  workspaceAgents,
   onAgentChange,
   onAgentRemove,
+  onAgentPromote,
+  onAgentUnlink,
   onGraphChange,
 }: {
   agent: PatternAgentDefinition;
@@ -127,17 +134,45 @@ function AgentNodeInspector({
   mode: OrchestrationMode;
   graph: PatternGraph;
   nodeId: string;
+  workspaceAgents: WorkspaceAgentDefinition[];
   onAgentChange: (agentId: string, patch: Partial<PatternAgentDefinition>) => void;
   onAgentRemove: (agentId: string) => void;
+  onAgentPromote: (agentId: string) => void;
+  onAgentUnlink: (agentId: string) => void;
   onGraphChange: (graph: PatternGraph) => void;
 }) {
   const model = findModel(agent.model, availableModels);
   const showReorder = mode === 'sequential' || mode === 'single' || mode === 'magentic';
   const canUp = showReorder && canMoveSequential(graph, nodeId, 'up');
   const canDown = showReorder && canMoveSequential(graph, nodeId, 'down');
+  const isLinked = Boolean(agent.workspaceAgentId);
+  const linkedWorkspaceAgent = isLinked
+    ? workspaceAgents.find((wa) => wa.id === agent.workspaceAgentId)
+    : undefined;
 
   return (
     <div className="space-y-4">
+      {/* Linked workspace agent banner */}
+      {isLinked && (
+        <div className="flex items-center justify-between rounded-lg border border-[var(--color-accent)]/20 bg-[var(--color-accent)]/5 px-3 py-2">
+          <div className="flex items-center gap-2">
+            <Link2 className="size-3.5 text-[var(--color-accent)]" />
+            <span className="text-[11px] text-[var(--color-text-secondary)]">
+              Linked to <strong className="text-[var(--color-text-primary)]">{linkedWorkspaceAgent?.name ?? 'unknown agent'}</strong>
+            </span>
+          </div>
+          <button
+            className="flex items-center gap-1 rounded px-2 py-1 text-[11px] text-[var(--color-text-muted)] transition hover:bg-[var(--color-surface-3)] hover:text-[var(--color-text-secondary)]"
+            onClick={() => onAgentUnlink(agent.id)}
+            title="Unlink from workspace agent (convert to inline)"
+            type="button"
+          >
+            <Unlink className="size-3" />
+            Unlink
+          </button>
+        </div>
+      )}
+
       <div className="flex items-center justify-between">
         <div className="flex items-center gap-2.5">
           <div className="flex size-8 items-center justify-center rounded-lg bg-[var(--color-surface-2)]">
@@ -218,6 +253,19 @@ function AgentNodeInspector({
         placeholder="System prompt for this agent..."
         value={agent.instructions}
       />
+
+      {/* Promote / Unlink action */}
+      {!isLinked && (
+        <button
+          className="flex w-full items-center justify-center gap-2 rounded-lg border border-dashed border-[var(--color-border)] px-3 py-2 text-[12px] text-[var(--color-text-muted)] transition hover:border-[var(--color-accent)]/30 hover:bg-[var(--color-accent)]/5 hover:text-[var(--color-accent)]"
+          onClick={() => onAgentPromote(agent.id)}
+          title="Save this agent to the workspace library for reuse across patterns"
+          type="button"
+        >
+          <Library className="size-3.5" />
+          Save to Agent Library
+        </button>
+      )}
     </div>
   );
 }
@@ -228,8 +276,11 @@ export function PatternGraphInspector({
   graph,
   mode,
   selectedNodeId,
+  workspaceAgents,
   onAgentChange,
   onAgentRemove,
+  onAgentPromote,
+  onAgentUnlink,
   onGraphChange,
 }: PatternGraphInspectorProps) {
   if (!selectedNodeId) {
@@ -268,8 +319,11 @@ export function PatternGraphInspector({
         mode={mode}
         graph={graph}
         nodeId={selectedNodeId}
+        workspaceAgents={workspaceAgents}
         onAgentChange={onAgentChange}
         onAgentRemove={onAgentRemove}
+        onAgentPromote={onAgentPromote}
+        onAgentUnlink={onAgentUnlink}
         onGraphChange={onGraphChange}
       />
     </div>