diff --git a/setup b/setup
index 08bf540a7..83b468bdd 100755
--- a/setup
+++ b/setup
@@ -195,7 +195,17 @@ while [ $# -gt 0 ]; do
 done
 
 case "$HOST" in
-  claude|codex|kiro|factory|opencode|cursor|slate|auto) ;;
+  claude|codex|kiro|factory|opencode|cursor|auto) ;;
+  slate)
+    echo ""
+    echo "Slate is not yet a first-class install target (docs/designs/SLATE_HOST.md —"
+    echo "blocked on the host-config refactor). Slate discovers skills from"
+    echo ".claude/skills as a compatibility fallback, so a Slate user is served by"
+    echo "the Claude install today:"
+    echo ""
+    echo "  ./setup --host claude"
+    echo ""
+    exit 0 ;;
   openclaw)
     echo ""
     echo "OpenClaw integration uses a different model — OpenClaw spawns Claude Code"
@@ -323,6 +333,14 @@ elif [ "$HOST" = "cursor" ]; then
   INSTALL_CURSOR=1
 fi
 
+# A host that passes --host validation but sets no INSTALL_* flag would
+# silently configure nothing and exit 0 (the #2361 slate failure class).
+# Fail loudly if a future host lands in the accept-list without a dispatch arm.
+if [ "$HOST" != "auto" ] && [ "$INSTALL_CLAUDE" -eq 0 ] && [ "$INSTALL_CODEX" -eq 0 ] && [ "$INSTALL_KIRO" -eq 0 ] && [ "$INSTALL_FACTORY" -eq 0 ] && [ "$INSTALL_OPENCODE" -eq 0 ] && [ "$INSTALL_CURSOR" -eq 0 ]; then
+  echo "Error: no install arm exists for host '$HOST' — it passed --host validation but sets no INSTALL_* flag, so setup would configure nothing and exit 0. This is a setup bug. Valid install targets: claude, codex, kiro, factory, opencode, cursor (informational: slate, openclaw, hermes, gbrain)." >&2
+  exit 1
+fi
+
 if [ "$MODEL_OVERRIDE_SET" -eq 1 ] && [ "$INSTALL_CODEX" -eq 0 ]; then
   echo "Error: --model is supported only when Codex is selected (--host codex or --host auto with Codex installed)." >&2
   exit 1
diff --git a/test/gen-skill-docs.test.ts b/test/gen-skill-docs.test.ts
index ba1b271f2..67aa46b18 100644
--- a/test/gen-skill-docs.test.ts
+++ b/test/gen-skill-docs.test.ts
@@ -2515,9 +2515,12 @@ describe('setup script validation', () => {
     expect(claudeSection).toContain('link_claude_root_skill_alias "$SOURCE_GSTACK_DIR" "$INSTALL_SKILLS_DIR"');
   });
 
-  test('setup supports --host auto|claude|codex|kiro|opencode|cursor|slate', () => {
+  test('setup supports --host auto|claude|codex|kiro|opencode|cursor; slate is informational', () => {
     expect(setupContent).toContain('--host');
-    expect(setupContent).toContain('claude|codex|kiro|factory|opencode|cursor|slate|auto');
+    // #2361: slate moved OUT of the install accept-list (it was accepted but
+    // never dispatched — a silent exit-0 no-op) into an informational arm.
+    expect(setupContent).toContain('claude|codex|kiro|factory|opencode|cursor|auto');
+    expect(setupContent).toMatch(/^ {2}slate\)/m);
   });
 
   test('auto mode detects claude, codex, kiro, and opencode binaries', () => {
diff --git a/test/setup-help.test.ts b/test/setup-help.test.ts
index f1cbcc6e3..01ad9b991 100644
--- a/test/setup-help.test.ts
+++ b/test/setup-help.test.ts
@@ -62,3 +62,67 @@ describe('setup: --help flag (#1133)', () => {
     expect(res.stdout).toContain('Usage:');
   });
 });
+
+describe('setup: host accept-list ↔ hosts/index.ts registry cross-check (#2361)', () => {
+  // The #2361 failure class: a host passes --host validation but has no
+  // install arm, so `./setup --host <it>` configures nothing and exits 0.
+  // This cross-check derives BOTH sides — the registry from hosts/index.ts
+  // and the case arms from setup — so adding a host to either place without
+  // the other goes red at the moment of the drift, not in a user report.
+
+  const content = fs.readFileSync(SETUP_SCRIPT, 'utf-8');
+
+  function hostCaseArms(): { installTargets: string[]; namedArms: string[] } {
+    const start = content.indexOf('case "$HOST" in');
+    expect(start).toBeGreaterThan(-1);
+    const block = content.slice(start, content.indexOf('\nesac', start));
+    // The pipe list is the install accept-list; single-name arms are informational.
+    const installTargets: string[] = [];
+    const namedArms: string[] = [];
+    for (const m of block.matchAll(/^ {2}([a-z|]+)\)/gm)) {
+      const names = m[1].split('|');
+      if (names.length > 1) installTargets.push(...names.filter((n) => n !== 'auto'));
+      else if (names[0] !== 'auto') namedArms.push(names[0]);
+    }
+    return { installTargets, namedArms };
+  }
+
+  test('registry names == accept-list (minus auto) + informational arms', async () => {
+    const { ALL_HOST_CONFIGS } = await import('../hosts/index');
+    const registered = ALL_HOST_CONFIGS.map((c: { name: string }) => c.name).sort();
+    const { installTargets, namedArms } = hostCaseArms();
+    const covered = [...new Set([...installTargets, ...namedArms])].sort();
+    expect(covered).toEqual(registered);
+  });
+
+  test('every accept-listed install target has a dispatch arm (the exact #2361 hole)', () => {
+    // Set-membership alone would have passed while slate sat accepted-but-
+    // unwired: the invariant that bites is accept-list ⊆ dispatch arms.
+    const { installTargets } = hostCaseArms();
+    expect(installTargets.length).toBeGreaterThan(0);
+    for (const host of installTargets) {
+      expect(content).toMatch(new RegExp(`\\[ "\\$HOST" = "${host}" \\]`));
+    }
+  });
+
+  test('slate informational arm: explains itself, points at --host claude, exit 0', () => {
+    const res = spawnSync('bash', [SETUP_SCRIPT, '--host', 'slate'], {
+      encoding: 'utf-8',
+      timeout: 5000,
+    });
+    expect(res.status).toBe(0);
+    expect(res.stdout).toContain('./setup --host claude');
+    expect(res.stdout).toContain('.claude/skills');
+    // It must not fall through into the installer.
+    expect(res.stdout).not.toMatch(/Installing|bun install|Building/);
+  });
+
+  test('zero-dispatch guard exists: unwired host errors loudly instead of exit-0 no-op', () => {
+    // The guard is only reachable when a future host is accepted but unwired,
+    // so pin its presence and shape statically: it must name the host, call
+    // itself a setup bug, and exit 1.
+    const guard = content.match(/no install arm exists for host[^\n]*\n\s*exit 1/);
+    expect(guard).toBeTruthy();
+    expect(content).toContain("[ \"$HOST\" != \"auto\" ]");
+  });
+});