Coverage measures the page's Node tests and runs the Rust on Postgres (#407)

page-unit.ts and native-bridge.ts run the page's script outside a
browser, so the page's coverage counted none of what they test, and
native.ts read as mostly untested. In a coverage run they now run the
script from a file of its own, named as the browser names it, under
NODE_V8_COVERAGE (scripts/coverage-node.sh, before the browser suite in
npm run coverage:page and coverage.sh api), and the report's teardown
takes their record in, mapped to web/src by the build's source map: the
page's lines went from 73.3% to 80.0% of 3,043, native.ts to 93 of 120.

The cargo tests in coverage.sh's container run on Postgres, as
production does, when IPX_TEST_DATABASE_URL names the _test database,
from the shell or else /src/.envrc (that variable only); on SQLite
without it. The integration tests' own files are left out of the
totals; a crate's inline mod tests cannot be on stable Rust.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/dom-stub.ts

@@ -7,6 +7,9 @@
 // native.ts replaces that surface on the element and a proxy that answers everything would prove
 // nothing about whether it worked.
 import vm from 'node:vm';
+import fs from 'node:fs';
+import path from 'node:path';
+import { pathToFileURL } from 'node:url';
 import { webcrypto } from 'node:crypto';
 
 // The VM's side is the page's script, whose types are its own (web/src): a test reaches into it by
@@ -142,4 +145,15 @@ class MediaElement {
   get readyState() { return this._ready; }
 }
 
-export { makeContext, vm, MediaElement };
+/// The name to run the page's script under. In a coverage run (IPX_COVERAGE=1, #407), a file of its
+/// own named as the browser names it, so NODE_V8_COVERAGE's record of it, which the page's report
+/// takes in (tests/ui/coverage-teardown.ts), maps back to web/src through its inline source map.
+function scriptName(js: string, name: string): string {
+  if (!process.env.IPX_COVERAGE) return name;
+  const file = path.resolve('target/coverage/node-page/app.js');
+  fs.mkdirSync(path.dirname(file), { recursive: true });
+  fs.writeFileSync(file, js);
+  return pathToFileURL(file).href;
+}
+
+export { makeContext, vm, MediaElement, scriptName };