fix(scripts): make the test stubs drain, and the raw-mode guard testable (#2147)

Copilot review round 5 — four findings, all in the suppressed block.

1+4. The regression stubs did `console.log(MARKER); process.exit(1)`.
     Writing to a PIPE is asynchronous and `process.exit()` tears the
     process down without draining, so the marker can be lost outright —
     and then the stub that pins the paint-then-die path fails as "exited
     before rendering", the neighbouring branch and the wrong diagnostic
     for the thing it guards.

     Worth recording that I met this mechanism last round and did not join
     the dots: probing the drain race, a 4MB write followed by
     `process.exit()` reached the parent with the marker missing
     entirely. That was noted as a reason the repro failed, while the same
     construct stayed in the stubs. Both now set `process.exitCode` and
     let the loop drain — still exiting immediately after the write — with
     a comment, since `process.exit()` is the more obvious spelling and
     will read as a simplification to the next person. Same fix for the
     `console.error("boom")` stub, whose assertion had the same exposure.

2.   DEFAULTS claimed "every one is a hard floor as well as a default",
     which contradicts `normalizeMs` (any finite positive value passes)
     and the suite two files over, which passes 400ms against a 2000ms
     default. It rejects the shape a bad env var produces, not smallness.

3.   The raw-mode forbidden-output check was unreachable from any test:
     the real PTY happy path only exercises the pattern NOT matching, so
     a regression breaking it would stay green forever — an
     acceptance-criterion guard with nothing guarding it, which is the
     recursive form of this PR's own complaint.

     Now a `runRenderSmoke` option (`forbidOutput`), so it runs inside the
     tested state machine and against the fully drained output.
     `smoke:tui` passes its pattern in and drops the post-hoc check. It
     can only turn a pass into a failure, never rewrite an existing
     failure's message: a crash reason is more useful than "and it also
     printed X", which is usually a symptom of that crash. Three tests —
     matching, not matching, and that asymmetry.

Verified: test:scripts 213/213; `smoke:tui OK — rendered "MCP Servers" at
360ms and was still running 2000ms later`; and the no-PTY shim still
fails through the refactored path.

Signed-off-by: Cliff Hall <cliff@futurescale.com>
Signed-off-by: cliffhall <cliff@futurescale.com>

scripts/smoke-tui.mjs

@@ -152,6 +152,16 @@ try {
         USERPROFILE: work,
       },
     },
+    // Belt and braces for the acceptance criterion this fix is measured
+    // against. Survival already implies it today, since the raw-mode throw is
+    // fatal — but if Ink ever degrades it to a warning, a TUI with no keyboard
+    // input would survive happily, and this smoke is the only thing watching.
+    forbidOutput: {
+      pattern: RAW_MODE_ERROR,
+      reason:
+        `TUI rendered and survived, but still logged the raw-mode error — ` +
+        `the pseudoterminal did not take effect (flavor: ${pty.flavor})`,
+    },
     warn: (m) => console.warn(m.replace(/^render-smoke/, "smoke:tui")),
   });
 } finally {
@@ -163,17 +173,6 @@ try {
   removeSafe(work, { label: "smoke:tui" });
 }
 
-// Belt and braces for the acceptance criterion this fix is measured against.
-// Survival already implies it today, since the raw-mode throw is fatal — but
-// if Ink ever degrades to a warning instead, a TUI with no keyboard input would
-// otherwise pass silently, and this smoke is the only thing watching.
-if (result.code === 0 && RAW_MODE_ERROR.test(result.output)) {
-  fail(
-    `TUI rendered and survived, but still logged the raw-mode error — the ` +
-      `pseudoterminal did not take effect (flavor: ${pty.flavor})`,
-  );
-}
-
 if (result.code === 0) {
   console.log(`smoke:tui OK — ${result.message}`);
   process.exit(0);