fix: stop the sdk-watch tests depending on the runner's environment

CI's `build` job went red on one case, `main refuses to run without a
repository`, which passed locally. The cause is ambient environment, not
the code under test: `main`'s `repo` parameter defaults to
`process.env.GITHUB_REPOSITORY`, which is UNSET on a developer machine
and SET on every Actions runner. Passing `undefined` therefore exercised
that default, so the throw happened locally and did not on CI.

`npm run local:gate` is a strict superset of CI's STAGES but not of its
ambient environment, so nothing local could have caught this. The test
now clears the variable around the assertion and restores it, which
makes both environments test the same thing.

The same defaulting applies to `output`, whose default is
`process.env.GITHUB_OUTPUT` — a real file on a runner, the one the job's
own outputs are read from. Every throwing case now pins it to
`undefined` via a `noAmbientOutput` helper. Nothing is written today
because these cases throw before the emit, but leaving the default in
place means a future case that stops throwing would append `filed=…` to
the live job output instead of failing an assertion.

Verified both ways: the suite is green with the variables unset, and
green with GITHUB_REPOSITORY and GITHUB_OUTPUT set as a runner sets them
— 574/574 across all of `scripts/`, with no file created at the
GITHUB_OUTPUT path.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019JWUZxLDnPgLQzjBrtk1x9
Signed-off-by: cliffhall <cliff@futurescale.com>

scripts/sdk-watch.test.mjs

@@ -392,6 +392,20 @@ function readFiled(path) {
   return JSON.parse(line.slice("filed=".length));
 }
 
+/**
+ * Options for a case that asserts a throw and so never emits.
+ *
+ * `output` is pinned to `undefined` rather than left to default. Its default is
+ * `process.env.GITHUB_OUTPUT`, which is a REAL FILE on an Actions runner — the
+ * one the job's own outputs are read from. These cases throw before reaching the
+ * emit, so nothing is written today, but leaving the default in place means a
+ * future case that stops throwing would append `filed=…` to the live job output
+ * instead of failing an assertion.
+ */
+function noAmbientOutput(readFile = fakeReadFile()) {
+  return { readFile, output: undefined };
+}
+
 test("main files nothing and emits an empty list when the whole SDK is current", () => {
   const spawn = fakeSpawn();
   const output = outputFile();
@@ -611,7 +625,7 @@ test("main throws when npm view fails rather than reporting a clean sweep", () =
   // registry outage becomes a green all-current night.
   const spawn = fakeSpawn({ npmStatus: 1 });
   assert.throws(
-    () => main("o/r", spawn, { readFile: fakeReadFile() }),
+    () => main("o/r", spawn, noAmbientOutput()),
     /npm view .* failed/,
   );
 });
@@ -619,7 +633,7 @@ test("main throws when npm view fails rather than reporting a clean sweep", () =
 test("main throws when npm view returns something that is not a version", () => {
   const spawn = fakeSpawn({ npmStdout: "\n" });
   assert.throws(
-    () => main("o/r", spawn, { readFile: fakeReadFile() }),
+    () => main("o/r", spawn, noAmbientOutput()),
     /unusable version/,
   );
 });
@@ -630,16 +644,28 @@ test("main propagates a failed issue creation", () => {
     createStatus: 1,
   });
   assert.throws(
-    () => main("o/r", spawn, { readFile: fakeReadFile() }),
+    () => main("o/r", spawn, noAmbientOutput()),
     /gh issue create failed/,
   );
 });
 
 test("main refuses to run without a repository", () => {
-  assert.throws(
-    () => main(undefined, fakeSpawn(), { readFile: fakeReadFile() }),
-    /GITHUB_REPOSITORY unset/,
-  );
+  // ⚠️ `repo` defaults to `process.env.GITHUB_REPOSITORY`, which is UNSET on a
+  // developer machine and SET on every Actions runner. So passing `undefined`
+  // exercises that default, and this assertion held locally while going red the
+  // first time CI ran it. Clear the variable so both environments test the same
+  // thing — `npm run local:gate` is a superset of CI's STAGES, but not of its
+  // ambient environment.
+  const saved = process.env.GITHUB_REPOSITORY;
+  delete process.env.GITHUB_REPOSITORY;
+  try {
+    assert.throws(
+      () => main(undefined, fakeSpawn(), noAmbientOutput()),
+      /GITHUB_REPOSITORY unset/,
+    );
+  } finally {
+    if (saved !== undefined) process.env.GITHUB_REPOSITORY = saved;
+  }
 });
 
 test("main fails on an SDK package the group table does not watch", () => {
@@ -649,5 +675,8 @@ test("main fails on an SDK package the group table does not watch", () => {
           dependencies: { "@modelcontextprotocol/something-new": "1.0.0" },
         })
       : JSON.stringify({ packages: {} });
-  assert.throws(() => main("o/r", fakeSpawn(), { readFile }), /something-new/);
+  assert.throws(
+    () => main("o/r", fakeSpawn(), noAmbientOutput(readFile)),
+    /something-new/,
+  );
 });