fix: the gate installs a fresh machine as the stable room it is

A fresh device.conf says CHANNEL=stable, and the gate asked the fresh
install's updater about canary's manifest, which that machine never reads.
Found running the gate on 0.2.6.6: the updater check failed before any
upgrade was tried. The package was not at fault.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

tests/test-deployment-support.sh

@@ -272,8 +272,11 @@ check("the repository copy is proven to be the gated file",
 gate = (root / "tools/release-gate.sh").read_text()
 gate_code = "\n".join(line for line in gate.splitlines()
                       if not line.lstrip().startswith("#"))
-check("the gate runs a fresh install",
-      '"$ROOT/tools/validate-trixie-release.sh" "$candidate"\n' in gate_code)
+check("the gate runs a fresh install, as the stable room a new machine is",
+      'env VALIDATION_CHANNEL=stable \\\n    "$ROOT/tools/validate-trixie-release.sh" "$candidate"\n'
+      in gate_code)
+check("which is what a fresh device.conf says",
+      "CHANNEL=stable" in (root / "lib/classroom_config.py").read_text())
 check("and the upgrade from what canary and stable serve, as rooms of each",
       "for channel in canary stable" in gate_code
       and 'VALIDATION_CHANNEL="$channel"' in gate_code)

tools/release-gate.sh

@@ -118,7 +118,10 @@ run() {
     record "PASS  $label  ($(( (SECONDS - started) / 60 )) min)"
 }
 
-run "fresh install of $version" \
+# A new machine is a stable room: that is what a fresh device.conf says,
+# so that is the manifest its updater is asked about.
+run "fresh install of $version (a new machine, on stable)" \
+    env VALIDATION_CHANNEL=stable \
     "$ROOT/tools/validate-trixie-release.sh" "$candidate"
 
 for channel in canary stable; do