Improve ACPX adapter configuration (#5290)

## Thinking Path

> - Paperclip orchestrates AI agents across several adapter
implementations.
> - ACPX is a local adapter path that can proxy Claude and Codex-style
execution.
> - Its configuration needed stronger schema defaults, provider-aware
model handling, and better UI support.
> - Plugin authors also need clear docs for managed resources.
> - This pull request improves ACPX adapter configuration and documents
plugin-managed resources.
> - The benefit is a more predictable adapter setup path without
changing unrelated control-plane behavior.

## What Changed

- Improved ACPX config schema, execution config handling, UI build
config, and route coverage.
- Added ACPX model filtering support and tests.
- Updated the agent config form and storybook coverage for ACPX
model/provider behavior.
- Expanded plugin authoring documentation for managed resources.

## Verification

- `pnpm install --frozen-lockfile`
- `pnpm exec vitest run server/src/__tests__/acpx-local-execute.test.ts
server/src/__tests__/adapter-routes.test.ts
ui/src/lib/acpx-model-filter.test.ts`

## Risks

- Low-to-medium risk: adapter configuration behavior changes can affect
ACPX users, but the change is isolated to ACPX/plugin-doc surfaces and
covered by targeted adapter tests.

## Model Used

- OpenAI GPT-5 Codex via Paperclip `codex_local` adapter, with
shell/git/GitHub CLI tool use.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

ui/src/lib/acpx-model-filter.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from "vitest";
+import { filterAcpxModelsByAgent } from "./acpx-model-filter";
+
+const mixedModels = [
+  { id: "claude-sonnet-4-6", label: "Claude: Claude Sonnet 4.6" },
+  { id: "gpt-5.3-codex", label: "Codex: gpt-5.3-codex" },
+  { id: "provider/custom-model", label: "Custom model" },
+];
+
+describe("filterAcpxModelsByAgent", () => {
+  it("keeps only Claude models when ACPX Claude is selected", () => {
+    expect(filterAcpxModelsByAgent(mixedModels, "claude").map((model) => model.id)).toEqual([
+      "claude-sonnet-4-6",
+    ]);
+  });
+
+  it("keeps only Codex models when ACPX Codex is selected", () => {
+    expect(filterAcpxModelsByAgent(mixedModels, "codex").map((model) => model.id)).toEqual([
+      "gpt-5.3-codex",
+    ]);
+  });
+
+  it("does not show built-in provider models for custom ACP commands", () => {
+    expect(filterAcpxModelsByAgent(mixedModels, "custom")).toEqual([]);
+  });
+});

ui/src/lib/acpx-model-filter.ts

@@ -0,0 +1,16 @@
+import type { AdapterModel } from "../api/agents";
+import { models as CLAUDE_LOCAL_MODELS } from "@paperclipai/adapter-claude-local";
+import { models as CODEX_LOCAL_MODELS } from "@paperclipai/adapter-codex-local";
+
+const claudeModelIds = new Set(CLAUDE_LOCAL_MODELS.map((model) => model.id));
+const codexModelIds = new Set(CODEX_LOCAL_MODELS.map((model) => model.id));
+
+export function filterAcpxModelsByAgent(models: AdapterModel[], acpxAgent: string): AdapterModel[] {
+  if (acpxAgent === "claude") {
+    return models.filter((model) => claudeModelIds.has(model.id) || model.label.startsWith("Claude: "));
+  }
+  if (acpxAgent === "codex") {
+    return models.filter((model) => codexModelIds.has(model.id) || model.label.startsWith("Codex: "));
+  }
+  return [];
+}