fix(agent): honor model:inherit and show subagents in /agents dialog

- Skip parseModel for "inherit" model value so subagents without an
  explicit model inherit the parent session's model instead of
  producing a ProviderModelNotFoundError
- Expose listAll() from local agent context returning all non-hidden
  agents regardless of mode
- Switch /agents dialog to listAll() with Primary/Subagents grouping
  so externally-installed subagents (e.g. get-shit-done) are visible
- Improve set() toast to distinguish subagents from missing agents

Tested with get-shit-done global install (~/.config/opencode/agents/).

Author: flacks

packages/opencode/src/agent/agent.ts

@@ -217,7 +217,7 @@ export namespace Agent {
           options: {},
           native: false,
         }
-      if (value.model) item.model = Provider.parseModel(value.model)
+      if (value.model && value.model !== "inherit") item.model = Provider.parseModel(value.model)
       item.variant = value.variant ?? item.variant
       item.prompt = value.prompt ?? item.prompt
       item.description = value.description ?? item.description

packages/opencode/src/cli/cmd/tui/component/dialog-agent.tsx

@@ -8,11 +8,12 @@ export function DialogAgent() {
   const dialog = useDialog()
 
   const options = createMemo(() =>
-    local.agent.list().map((item) => {
+    local.agent.listAll().map((item) => {
       return {
         value: item.name,
         title: item.name,
         description: item.native ? "native" : item.description,
+        category: item.mode === "subagent" ? "Subagents" : "Primary",
       }
     }),
   )

packages/opencode/src/cli/cmd/tui/context/local.tsx

@@ -56,16 +56,26 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
         list() {
           return agents()
         },
+        listAll() {
+          return visibleAgents()
+        },
         current() {
           return agents().find((x) => x.name === agentStore.current)!
         },
         set(name: string) {
-          if (!agents().some((x) => x.name === name))
+          const target = visibleAgents().find((x) => x.name === name)
+          if (!target)
             return toast.show({
               variant: "warning",
               message: `Agent not found: ${name}`,
               duration: 3000,
             })
+          if (target.mode === "subagent")
+            return toast.show({
+              variant: "warning",
+              message: `${name} is a subagent — invoke it with @${name}`,
+              duration: 3000,
+            })
           setAgentStore("current", name)
         },
         move(direction: 1 | -1) {