Add OpenAI Codex adapter (.codex/skills/), 4 tool adapters total

Adapters: github-copilot, claude, codex, opencode
Agent values: github, claude, codex, opencode
85 tests passing

Author: ClankerGuru

README.md

@@ -52,6 +52,7 @@ zone.clanker.openspec.agents=github
 |-------------------|---------------------------------------------|
 | `github`          | Generates GitHub Copilot files (`.github/`)   |
 | `claude`          | Generates Claude Code files (`.claude/`)      |
+| `codex`           | Generates OpenAI Codex files (`.codex/`)      |
 | `opencode`        | Generates OpenCode/Crush files (`.opencode/`) |
 | `github,claude`   | Generates for multiple (comma-separated)      |
 | `none` or empty   | Cleans all generated files                    |

build.gradle.kts

@@ -38,8 +38,8 @@ gradlePlugin {
             id = "zone.clanker.gradle"
             implementationClass = "zone.clanker.gradle.OpenSpecSettingsPlugin"
             displayName = "OpenSpec Gradle Plugin"
-            description = "Settings plugin that generates Markdown skill and command files for AI coding assistants (GitHub Copilot, Claude Code, OpenCode/Crush). Auto-applies to root project via init script."
-            tags.set(listOf("ai", "copilot", "claude", "opencode", "openspec", "skills", "prompts", "coding-assistant"))
+            description = "Settings plugin that generates Markdown skill and command files for AI coding assistants (GitHub Copilot, Claude Code, OpenAI Codex, OpenCode/Crush). Auto-applies to root project via init script."
+            tags.set(listOf("ai", "copilot", "claude", "codex", "opencode", "openspec", "skills", "prompts", "coding-assistant"))
         }
     }
 }

src/main/kotlin/zone/clanker/gradle/OpenSpecSettingsPlugin.kt

@@ -25,6 +25,7 @@ class OpenSpecSettingsPlugin : Plugin<Settings> {
         private val AGENT_MAP = mapOf(
             "github" to "github-copilot",
             "claude" to "claude",
+            "codex" to "codex",
             "opencode" to "opencode"
         )
 

src/main/kotlin/zone/clanker/gradle/generators/ToolAdapter.kt

@@ -101,6 +101,24 @@ object GitHubCopilotAdapter : ToolAdapter {
     override fun formatSkillFile(content: SkillContent) = formatSkillWithFrontmatter(content)
 }
 
+object CodexAdapter : ToolAdapter {
+    override val toolId = "codex"
+    // Codex uses .codex/skills/<name>/SKILL.md — skills are invoked via $skill-name
+    // Codex doesn't have a separate commands directory — skills ARE the commands
+    override fun getCommandFilePath(commandId: String) = ".codex/skills/opsx-$commandId/SKILL.md"
+    override fun formatCommandFile(content: CommandContent) = buildString {
+        // Format commands as skills since Codex unifies them
+        val asSkill = SkillContent(
+            dirName = "opsx-${content.id}",
+            description = content.description,
+            instructions = content.body
+        )
+        append(formatSkillWithFrontmatter(asSkill))
+    }
+    override fun getSkillFilePath(skillDirName: String) = ".codex/skills/$skillDirName/SKILL.md"
+    override fun formatSkillFile(content: SkillContent) = formatSkillWithFrontmatter(content)
+}
+
 object OpenCodeAdapter : ToolAdapter {
     override val toolId = "opencode"
     // OpenCode reads commands from .opencode/commands/*.md (project-level)
@@ -123,6 +141,7 @@ object ToolAdapterRegistry {
     private val adapters = mapOf(
         "claude" to ClaudeAdapter,
         "github-copilot" to GitHubCopilotAdapter,
+        "codex" to CodexAdapter,
         "opencode" to OpenCodeAdapter
     )
 

src/test/kotlin/zone/clanker/gradle/ToolAdapterTest.kt

@@ -98,12 +98,12 @@ class ToolAdapterTest {
 
     @Test
     fun `ToolAdapterRegistry supportedTools lists all tools`() {
-        assertEquals(setOf("claude", "github-copilot", "opencode"), ToolAdapterRegistry.supportedTools())
+        assertEquals(setOf("claude", "github-copilot", "codex", "opencode"), ToolAdapterRegistry.supportedTools())
     }
 
     @Test
-    fun `ToolAdapterRegistry all returns three adapters`() {
-        assertEquals(3, ToolAdapterRegistry.all().size)
+    fun `ToolAdapterRegistry all returns four adapters`() {
+        assertEquals(4, ToolAdapterRegistry.all().size)
     }
 
     // ── Agent parsing ────────────────────────────────────
@@ -154,6 +154,37 @@ class ToolAdapterTest {
         assertEquals(listOf("github-copilot", "claude"), OpenSpecSettingsPlugin.parseAgents("GitHub,Claude"))
     }
 
+    // ── Codex adapter ────────────────────────────────────
+
+    @Test
+    fun `CodexAdapter command path uses codex skills dir`() {
+        // Codex unifies commands as skills
+        assertEquals(".codex/skills/opsx-propose/SKILL.md", CodexAdapter.getCommandFilePath("propose"))
+    }
+
+    @Test
+    fun `CodexAdapter skill path uses codex skills dir`() {
+        assertEquals(".codex/skills/test-skill/SKILL.md", CodexAdapter.getSkillFilePath("test-skill"))
+    }
+
+    @Test
+    fun `CodexAdapter command format has YAML frontmatter`() {
+        val output = CodexAdapter.formatCommandFile(sampleCommand)
+        assertTrue(output.startsWith("---\n"))
+        assertTrue(output.contains("name: opsx-test-cmd"))
+        assertTrue(output.contains("description:"))
+    }
+
+    @Test
+    fun `ToolAdapterRegistry returns CodexAdapter for codex`() {
+        assertEquals(CodexAdapter, ToolAdapterRegistry.get("codex"))
+    }
+
+    @Test
+    fun `parseAgents maps codex to codex`() {
+        assertEquals(listOf("codex"), OpenSpecSettingsPlugin.parseAgents("codex"))
+    }
+
     // ── OpenCode adapter ─────────────────────────────────
 
     @Test