R0: module-migration rails (src/ serving, live-edit cache, scriptType loading, governance) (#812)

Host enablement for the plugin ES-module migration: sandboxed /api/plugins/{id}/src/ serving, no-cache+weak-ETag/304 live-edit caching on src/+screen.js+assets, scriptType:module loader injection + scriptType/minHost manifest passthrough; constitution v1.2.0 + module playbook + signed size-exemptions register + maintainer/CI-only ESLint gate; rerunnable perf-baseline harness. Reviewed by Codex (local), Copilot, and CodeRabbit.

tests/test_plugin_src_route.py

@@ -0,0 +1,140 @@
+"""Tests for the plugin `src/` module-serving route and the live-edit cache
+contract added in R0 (module-migration rails).
+
+Covers:
+  * GET /api/plugins/{id}/src/{path} serves a plugin's ES-module source tree
+    with the right Content-Type, including nested paths.
+  * Path containment: `..`, absolute, and NUL are rejected (404) — the same
+    `safe_join` guard the assets/ route uses.
+  * The live-edit cache contract: no-cache + a weak ETag, a bodyless 304 on
+    matching If-None-Match, and no stale 304 after an in-place edit.
+  * screen.js and assets/ now also emit an ETag and honor If-None-Match
+    (previously screen.js sent no headers and assets/ never returned 304).
+
+The routes read the module-global `plugins.LOADED_PLUGINS`, so each test
+registers a fake ready plugin directly (save/restore that global) and drives
+`register_plugin_api` on a fresh FastAPI app — no full server import needed.
+"""
+
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+import plugins
+
+
+PLUGIN_ID = "srctest"
+
+
+@pytest.fixture()
+def client(tmp_path):
+    """A TestClient with `register_plugin_api` wired and a single fake ready
+    plugin whose dir (`tmp_path`) holds a src/ tree, an asset, and a screen.js.
+    Restores LOADED_PLUGINS afterward."""
+    (tmp_path / "src").mkdir()
+    (tmp_path / "src" / "main.js").write_text("import './util/x.js';\nexport const boot = 1;\n")
+    (tmp_path / "src" / "util").mkdir()
+    (tmp_path / "src" / "util" / "x.js").write_text("export const x = 42;\n")
+    (tmp_path / "src" / "theme.css").write_text(".a{color:red}\n")
+    (tmp_path / "assets").mkdir()
+    (tmp_path / "assets" / "worklet.js").write_text("// worklet\n")
+    (tmp_path / "screen.js").write_text("import './src/main.js';\n")
+
+    saved = list(plugins.LOADED_PLUGINS)
+    plugins.LOADED_PLUGINS.clear()
+    plugins.LOADED_PLUGINS.append({
+        "id": PLUGIN_ID,
+        "status": "ready",
+        "_dir": tmp_path,
+        "_manifest": {"script": "screen.js", "scriptType": "module"},
+    })
+    app = FastAPI()
+    plugins.register_plugin_api(app)
+    c = TestClient(app, raise_server_exceptions=True)
+    try:
+        yield c, tmp_path
+    finally:
+        c.close()
+        plugins.LOADED_PLUGINS.clear()
+        plugins.LOADED_PLUGINS.extend(saved)
+
+
+def test_src_file_served_with_js_media_type(client):
+    c, _ = client
+    r = c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js")
+    assert r.status_code == 200
+    # Either application/javascript or text/javascript is a valid module-script
+    # MIME (guess_type returns text/javascript on newer platforms); browsers
+    # accept both for <script type=module>.
+    assert "javascript" in r.headers["content-type"]
+    assert "export const boot" in r.text
+    assert r.headers["cache-control"] == "no-cache"
+    assert r.headers.get("etag")
+
+
+def test_src_nested_path_and_css_media_type(client):
+    c, _ = client
+    assert c.get(f"/api/plugins/{PLUGIN_ID}/src/util/x.js").status_code == 200
+    r = c.get(f"/api/plugins/{PLUGIN_ID}/src/theme.css")
+    assert r.status_code == 200
+    assert r.headers["content-type"].startswith("text/css")
+
+
+@pytest.mark.parametrize("bad", [
+    "..%2f..%2fplugin.json",     # escape the src/ dir
+    "..%2f..%2f..%2fetc%2fpasswd",
+    "%2fetc%2fpasswd",           # absolute
+    "util%2f..%2f..%2fscreen.js",
+])
+def test_src_traversal_rejected(client, bad):
+    c, _ = client
+    assert c.get(f"/api/plugins/{PLUGIN_ID}/src/{bad}").status_code == 404
+
+
+def test_src_missing_is_404(client):
+    c, _ = client
+    assert c.get(f"/api/plugins/{PLUGIN_ID}/src/nope.js").status_code == 404
+
+
+def test_src_conditional_304(client):
+    c, _ = client
+    r1 = c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js")
+    etag = r1.headers["etag"]
+    r2 = c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js", headers={"If-None-Match": etag})
+    assert r2.status_code == 304
+    assert r2.content == b""
+
+
+def test_src_no_stale_304_after_edit(client):
+    c, root = client
+    etag = c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js").headers["etag"]
+    (root / "src" / "main.js").write_text("export const boot = 2;  // edited, longer body\n")
+    r = c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js", headers={"If-None-Match": etag})
+    assert r.status_code == 200
+    assert "boot = 2" in r.text
+    assert r.headers["etag"] != etag
+
+
+def test_screen_js_now_conditional(client):
+    c, _ = client
+    r1 = c.get(f"/api/plugins/{PLUGIN_ID}/screen.js")
+    assert r1.status_code == 200
+    assert r1.headers["cache-control"] == "no-cache"
+    etag = r1.headers["etag"]
+    r2 = c.get(f"/api/plugins/{PLUGIN_ID}/screen.js", headers={"If-None-Match": etag})
+    assert r2.status_code == 304
+
+
+def test_asset_now_conditional(client):
+    c, _ = client
+    r1 = c.get(f"/api/plugins/{PLUGIN_ID}/assets/worklet.js")
+    assert r1.status_code == 200
+    etag = r1.headers["etag"]
+    r2 = c.get(f"/api/plugins/{PLUGIN_ID}/assets/worklet.js", headers={"If-None-Match": etag})
+    assert r2.status_code == 304
+
+
+def test_unready_plugin_src_is_404(client):
+    c, _ = client
+    plugins.LOADED_PLUGINS[0]["status"] = "installing"
+    assert c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js").status_code == 404