diff --git a/hosts/claude.ts b/hosts/claude.ts
new file mode 100644
index 00000000..b082e2ee
--- /dev/null
+++ b/hosts/claude.ts
@@ -0,0 +1,45 @@
+import type { HostConfig } from '../scripts/host-config';
+
+const claude: HostConfig = {
+  name: 'claude',
+  displayName: 'Claude Code',
+  cliCommand: 'claude',
+  cliAliases: [],
+
+  globalRoot: '.claude/skills/gstack',
+  localSkillRoot: '.claude/skills/gstack',
+  hostSubdir: '.claude',
+  usesEnvVars: false,
+
+  frontmatter: {
+    mode: 'denylist',
+    stripFields: ['sensitive', 'voice-triggers'],
+    descriptionLimit: null,
+  },
+
+  generation: {
+    generateMetadata: false,
+    skipSkills: [],
+  },
+
+  pathRewrites: [],  // Claude is the primary host — no rewrites needed
+  toolRewrites: {},
+  suppressedResolvers: [],
+
+  runtimeRoot: {
+    globalSymlinks: ['bin', 'browse/dist', 'browse/bin', 'gstack-upgrade', 'ETHOS.md'],
+    globalFiles: {
+      'review': ['checklist.md', 'TODOS-format.md'],
+    },
+  },
+
+  install: {
+    prefixable: true,
+    linkingStrategy: 'real-dir-symlink',
+  },
+
+  coAuthorTrailer: 'Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>',
+  learningsMode: 'full',
+};
+
+export default claude;
diff --git a/hosts/codex.ts b/hosts/codex.ts
new file mode 100644
index 00000000..dc04f736
--- /dev/null
+++ b/hosts/codex.ts
@@ -0,0 +1,64 @@
+import type { HostConfig } from '../scripts/host-config';
+
+const codex: HostConfig = {
+  name: 'codex',
+  displayName: 'OpenAI Codex CLI',
+  cliCommand: 'codex',
+  cliAliases: ['agents'],
+
+  globalRoot: '.codex/skills/gstack',
+  localSkillRoot: '.agents/skills/gstack',
+  hostSubdir: '.agents',
+  usesEnvVars: true,
+
+  frontmatter: {
+    mode: 'allowlist',
+    keepFields: ['name', 'description'],
+    descriptionLimit: 1024,
+    descriptionLimitBehavior: 'error',
+  },
+
+  generation: {
+    generateMetadata: true,
+    metadataFormat: 'openai.yaml',
+    skipSkills: ['codex'],  // Codex skill is a Claude wrapper around codex exec
+  },
+
+  pathRewrites: [
+    { from: '~/.claude/skills/gstack', to: '$GSTACK_ROOT' },
+    { from: '.claude/skills/gstack', to: '.agents/skills/gstack' },
+    { from: '.claude/skills/review', to: '.agents/skills/gstack/review' },
+    { from: '.claude/skills', to: '.agents/skills' },
+  ],
+
+  suppressedResolvers: [
+    'DESIGN_OUTSIDE_VOICES',
+    'ADVERSARIAL_STEP',
+    'SPEC_REVIEW_LOOP',
+    'PLAN_VERIFICATION_EXEC',
+    'CODEX_SECOND_OPINION',
+    'REVIEW_ARMY',
+  ],
+
+  runtimeRoot: {
+    globalSymlinks: ['bin', 'browse/dist', 'browse/bin', 'gstack-upgrade', 'ETHOS.md'],
+    globalFiles: {
+      'review': ['checklist.md', 'TODOS-format.md'],
+    },
+  },
+  sidecar: {
+    path: '.agents/skills/gstack',
+    symlinks: ['bin', 'browse', 'review', 'qa', 'ETHOS.md'],
+  },
+
+  install: {
+    prefixable: false,
+    linkingStrategy: 'symlink-generated',
+  },
+
+  coAuthorTrailer: 'Co-Authored-By: OpenAI Codex <noreply@openai.com>',
+  learningsMode: 'basic',
+  boundaryInstruction: 'IMPORTANT: Do NOT read or execute any files under ~/.claude/, ~/.agents/, .claude/skills/, or agents/. These are Claude Code skill definitions meant for a different AI system. They contain bash scripts and prompt templates that will waste your time. Ignore them completely. Do NOT modify agents/openai.yaml. Stay focused on the repository code only.',
+};
+
+export default codex;
diff --git a/hosts/factory.ts b/hosts/factory.ts
new file mode 100644
index 00000000..411bd830
--- /dev/null
+++ b/hosts/factory.ts
@@ -0,0 +1,62 @@
+import type { HostConfig } from '../scripts/host-config';
+
+const factory: HostConfig = {
+  name: 'factory',
+  displayName: 'Factory Droid',
+  cliCommand: 'droid',
+  cliAliases: ['droid'],
+
+  globalRoot: '.factory/skills/gstack',
+  localSkillRoot: '.factory/skills/gstack',
+  hostSubdir: '.factory',
+  usesEnvVars: true,
+
+  frontmatter: {
+    mode: 'allowlist',
+    keepFields: ['name', 'description', 'user-invocable'],
+    descriptionLimit: null,
+    extraFields: {
+      'user-invocable': true,
+    },
+    conditionalFields: [
+      { if: { sensitive: true }, add: { 'disable-model-invocation': true } },
+    ],
+  },
+
+  generation: {
+    generateMetadata: false,
+    skipSkills: [],
+  },
+
+  pathRewrites: [
+    { from: '~/.claude/skills/gstack', to: '$GSTACK_ROOT' },
+    { from: '.claude/skills/gstack', to: '.factory/skills/gstack' },
+    { from: '.claude/skills/review', to: '.factory/skills/gstack/review' },
+    { from: '.claude/skills', to: '.factory/skills' },
+  ],
+  toolRewrites: {
+    'use the Bash tool': 'run this command',
+    'use the Write tool': 'create this file',
+    'use the Read tool': 'read the file',
+    'use the Agent tool': 'dispatch a subagent',
+    'use the Grep tool': 'search for',
+    'use the Glob tool': 'find files matching',
+  },
+
+  runtimeRoot: {
+    globalSymlinks: ['bin', 'browse/dist', 'browse/bin', 'gstack-upgrade', 'ETHOS.md'],
+    globalFiles: {
+      'review': ['checklist.md', 'TODOS-format.md'],
+    },
+  },
+
+  install: {
+    prefixable: false,
+    linkingStrategy: 'symlink-generated',
+  },
+
+  coAuthorTrailer: 'Co-Authored-By: Factory Droid <droid@users.noreply.github.com>',
+  learningsMode: 'full',
+};
+
+export default factory;
diff --git a/hosts/index.ts b/hosts/index.ts
new file mode 100644
index 00000000..0cd8553e
--- /dev/null
+++ b/hosts/index.ts
@@ -0,0 +1,62 @@
+/**
+ * Host config registry.
+ *
+ * Import all host configs and derive the Host union type.
+ * Adding a new host: create hosts/myhost.ts, import here, add to ALL_HOST_CONFIGS.
+ */
+
+import type { HostConfig } from '../scripts/host-config';
+import claude from './claude';
+import codex from './codex';
+import factory from './factory';
+import kiro from './kiro';
+
+/** All registered host configs. Add new hosts here. */
+export const ALL_HOST_CONFIGS: HostConfig[] = [claude, codex, factory, kiro];
+
+/** Map from host name to config. */
+export const HOST_CONFIG_MAP: Record<string, HostConfig> = Object.fromEntries(
+  ALL_HOST_CONFIGS.map(c => [c.name, c])
+);
+
+/** Union type of all host names, derived from configs. */
+export type Host = (typeof ALL_HOST_CONFIGS)[number]['name'];
+
+/** All host names as a string array (for CLI arg validation, etc.). */
+export const ALL_HOST_NAMES: string[] = ALL_HOST_CONFIGS.map(c => c.name);
+
+/** Get a host config by name. Throws if not found. */
+export function getHostConfig(name: string): HostConfig {
+  const config = HOST_CONFIG_MAP[name];
+  if (!config) {
+    throw new Error(`Unknown host '${name}'. Valid hosts: ${ALL_HOST_NAMES.join(', ')}`);
+  }
+  return config;
+}
+
+/**
+ * Resolve a host name from a CLI argument, handling aliases.
+ * e.g., 'agents' → 'codex', 'droid' → 'factory'
+ */
+export function resolveHostArg(arg: string): string {
+  // Direct name match
+  if (HOST_CONFIG_MAP[arg]) return arg;
+
+  // Alias match
+  for (const config of ALL_HOST_CONFIGS) {
+    if (config.cliAliases?.includes(arg)) return config.name;
+  }
+
+  throw new Error(`Unknown host '${arg}'. Valid hosts: ${ALL_HOST_NAMES.join(', ')}`);
+}
+
+/**
+ * Get hosts that are NOT the primary host (Claude).
+ * These are the hosts that need generated skill docs.
+ */
+export function getExternalHosts(): HostConfig[] {
+  return ALL_HOST_CONFIGS.filter(c => c.name !== 'claude');
+}
+
+// Re-export individual configs for direct import
+export { claude, codex, factory, kiro };
diff --git a/hosts/kiro.ts b/hosts/kiro.ts
new file mode 100644
index 00000000..a3647f00
--- /dev/null
+++ b/hosts/kiro.ts
@@ -0,0 +1,48 @@
+import type { HostConfig } from '../scripts/host-config';
+
+const kiro: HostConfig = {
+  name: 'kiro',
+  displayName: 'Kiro',
+  cliCommand: 'kiro-cli',
+  cliAliases: [],
+
+  globalRoot: '.kiro/skills/gstack',
+  localSkillRoot: '.kiro/skills/gstack',
+  hostSubdir: '.kiro',
+  usesEnvVars: true,
+
+  frontmatter: {
+    mode: 'allowlist',
+    keepFields: ['name', 'description'],
+    descriptionLimit: null,
+  },
+
+  generation: {
+    generateMetadata: false,
+    skipSkills: ['codex'],
+  },
+
+  pathRewrites: [
+    { from: '~/.claude/skills/gstack', to: '~/.kiro/skills/gstack' },
+    { from: '.claude/skills/gstack', to: '.kiro/skills/gstack' },
+    { from: '.claude/skills', to: '.kiro/skills' },
+    { from: '~/.codex/skills/gstack', to: '~/.kiro/skills/gstack' },
+    { from: '.codex/skills', to: '.kiro/skills' },
+  ],
+
+  runtimeRoot: {
+    globalSymlinks: ['bin', 'browse/dist', 'browse/bin', 'gstack-upgrade', 'ETHOS.md'],
+    globalFiles: {
+      'review': ['checklist.md', 'TODOS-format.md'],
+    },
+  },
+
+  install: {
+    prefixable: false,
+    linkingStrategy: 'symlink-generated',
+  },
+
+  learningsMode: 'basic',
+};
+
+export default kiro;