test: cover the $schema layout in the integration fixture

tests/integration/fixtures/reference/plugin.json

@@ -1,4 +1,5 @@
 {
+  "$schema": "https://agent-plugins.org/schemas/1.0.0/plugin.schema.json",
   "name": "demo",
   "version": "0.1.0",
   "description": "Reference plugin for integration tests.",

tests/integration/test_antigravity.py

@@ -1,6 +1,11 @@
 """Antigravity end-to-end via folder install: `agy plugin install <dir>` loads the
 skill and MCP server, and an ambient env var reaches the server.
 
+Checks:
+    1. `agy plugin install <dir>` accepts the generated files.
+    2. It reports exactly one skill and one MCP server.
+    3. An ambient env var reaches the MCP server.
+
 AGY forwards the ambient environment. It can't resolve a `./` command, so we point
 it at the committed probe by absolute path. Auth lives under HOME (can't isolate),
 so we install into the real home; the `_clean_agy` fixture uninstalls before and

tests/integration/test_claude.py

@@ -2,6 +2,13 @@
 skill, `--config` sets the userConfig the server resolves
 (`${user_config.demo_host}`), and a session starts the server (via the generated
 `${CLAUDE_PLUGIN_ROOT}` command). Needs a session (auth), so it's `integration`.
+
+Checks:
+    1. `plugin marketplace add` + `plugin install` accept the generated files.
+    2. `plugin details` reports the skill.
+    3. `--config demo_host=...` sets the userConfig declared in the manifest.
+    4. A session starts the server via `${CLAUDE_PLUGIN_ROOT}`, and the config
+       value arrives as DEMO_HOST (`${user_config.demo_host}` resolved).
 """
 
 from __future__ import annotations

tests/integration/test_codex.py

@@ -1,6 +1,13 @@
 """Codex end-to-end via folder install: the plugin installs, its MCP server starts,
 and a user env var resolves into it.
 
+Checks:
+    1. Marketplace install accepts the generated files.
+    2. A session starts the MCP server.
+    3. A user env var reaches it, i.e. Codex applied the `.codex-plugin/`
+       `env_vars` overlay to the spec server. **Needs Codex 0.150.0+**; older
+       versions read the spec mcp.json only and drop the variable.
+
 Codex-legacy can't resolve a `./` command, so we point it at the committed probe
 by absolute path. Needs a session (auth), so it's marked `integration`.
 """

tests/integration/test_gemini.py

@@ -2,6 +2,12 @@
 the extension and its skill, the generated `${extensionPath}` command resolves the
 committed probe, and an ambient env var reaches the server.
 
+Checks:
+    1. `gemini extensions install <dir>` accepts the generated extension.
+    2. The extension and its skill are listed after install.
+    3. The `${extensionPath}` command in gemini-extension.json resolves.
+    4. An ambient env var reaches the MCP server.
+
 Gemini forwards the ambient environment. It prompts to trust the folder (answered
 on stdin) and installs into the real home; the `_clean_gemini` fixture uninstalls
 before and after (before too, to recover from a crashed prior run).