diff --git a/tools/cli/installers/lib/ide/_base-ide.js b/tools/cli/installers/lib/ide/_base-ide.js
index 25122ade..5ee39cb6 100644
--- a/tools/cli/installers/lib/ide/_base-ide.js
+++ b/tools/cli/installers/lib/ide/_base-ide.js
@@ -601,6 +601,18 @@ class BaseIdeSetup {
       .join(' ');
   }
 
+  /**
+   * Flatten a relative path to a single filename for flat slash command naming
+   * Example: 'module/agents/name.md' -> 'bmad-module-agents-name.md'
+   * Used by IDEs that ignore directory structure for slash commands (e.g., Antigravity, Codex)
+   * @param {string} relativePath - Relative path to flatten
+   * @returns {string} Flattened filename with 'bmad-' prefix
+   */
+  flattenFilename(relativePath) {
+    const sanitized = relativePath.replaceAll(/[/\\]/g, '-');
+    return `bmad-${sanitized}`;
+  }
+
   /**
    * Create agent configuration file
    * @param {string} bmadDir - BMAD installation directory
diff --git a/tools/cli/installers/lib/ide/antigravity.js b/tools/cli/installers/lib/ide/antigravity.js
new file mode 100644
index 00000000..3bccd911
--- /dev/null
+++ b/tools/cli/installers/lib/ide/antigravity.js
@@ -0,0 +1,463 @@
+const path = require('node:path');
+const { BaseIdeSetup } = require('./_base-ide');
+const chalk = require('chalk');
+const { getProjectRoot, getSourcePath, getModulePath } = require('../../../lib/project-root');
+const { WorkflowCommandGenerator } = require('./shared/workflow-command-generator');
+const { TaskToolCommandGenerator } = require('./shared/task-tool-command-generator');
+const { AgentCommandGenerator } = require('./shared/agent-command-generator');
+const {
+  loadModuleInjectionConfig,
+  shouldApplyInjection,
+  filterAgentInstructions,
+  resolveSubagentFiles,
+} = require('./shared/module-injections');
+const { getAgentsFromBmad, getAgentsFromDir } = require('./shared/bmad-artifacts');
+
+/**
+ * Google Antigravity IDE setup handler
+ *
+ * Uses .agent/workflows/ directory for slash commands
+ */
+class AntigravitySetup extends BaseIdeSetup {
+  constructor() {
+    super('antigravity', 'Google Antigravity', false);
+    this.configDir = '.agent';
+    this.workflowsDir = 'workflows';
+  }
+
+  /**
+   * Collect configuration choices before installation
+   * @param {Object} options - Configuration options
+   * @returns {Object} Collected configuration
+   */
+  async collectConfiguration(options = {}) {
+    const config = {
+      subagentChoices: null,
+      installLocation: null,
+    };
+
+    const sourceModulesPath = getSourcePath('modules');
+    const modules = options.selectedModules || [];
+
+    for (const moduleName of modules) {
+      // Check for Antigravity sub-module injection config in SOURCE directory
+      const injectionConfigPath = path.join(sourceModulesPath, moduleName, 'sub-modules', 'antigravity', 'injections.yaml');
+
+      if (await this.exists(injectionConfigPath)) {
+        const fs = require('fs-extra');
+        const yaml = require('js-yaml');
+
+        try {
+          // Load injection configuration
+          const configContent = await fs.readFile(injectionConfigPath, 'utf8');
+          const injectionConfig = yaml.load(configContent);
+
+          // Ask about subagents if they exist and we haven't asked yet
+          if (injectionConfig.subagents && !config.subagentChoices) {
+            config.subagentChoices = await this.promptSubagentInstallation(injectionConfig.subagents);
+
+            if (config.subagentChoices.install !== 'none') {
+              // Ask for installation location
+              const inquirer = require('inquirer');
+              const locationAnswer = await inquirer.prompt([
+                {
+                  type: 'list',
+                  name: 'location',
+                  message: 'Where would you like to install Antigravity subagents?',
+                  choices: [
+                    { name: 'Project level (.agent/agents/)', value: 'project' },
+                    { name: 'User level (~/.agent/agents/)', value: 'user' },
+                  ],
+                  default: 'project',
+                },
+              ]);
+              config.installLocation = locationAnswer.location;
+            }
+          }
+        } catch (error) {
+          console.log(chalk.yellow(`  Warning: Failed to process ${moduleName} features: ${error.message}`));
+        }
+      }
+    }
+
+    return config;
+  }
+
+  /**
+   * Cleanup old BMAD installation before reinstalling
+   * @param {string} projectDir - Project directory
+   */
+  async cleanup(projectDir) {
+    const fs = require('fs-extra');
+    const bmadWorkflowsDir = path.join(projectDir, this.configDir, this.workflowsDir, 'bmad');
+
+    if (await fs.pathExists(bmadWorkflowsDir)) {
+      await fs.remove(bmadWorkflowsDir);
+      console.log(chalk.dim(`  Removed old BMAD workflows from ${this.name}`));
+    }
+  }
+
+  /**
+   * Setup Antigravity IDE configuration
+   * @param {string} projectDir - Project directory
+   * @param {string} bmadDir - BMAD installation directory
+   * @param {Object} options - Setup options
+   */
+  async setup(projectDir, bmadDir, options = {}) {
+    // Store project directory for use in processContent
+    this.projectDir = projectDir;
+
+    console.log(chalk.cyan(`Setting up ${this.name}...`));
+
+    // Clean up old BMAD installation first
+    await this.cleanup(projectDir);
+
+    // Create .agent/workflows directory structure
+    const agentDir = path.join(projectDir, this.configDir);
+    const workflowsDir = path.join(agentDir, this.workflowsDir);
+    const bmadWorkflowsDir = path.join(workflowsDir, 'bmad');
+
+    await this.ensureDir(bmadWorkflowsDir);
+
+    // Generate agent launchers using AgentCommandGenerator
+    // This creates small launcher files that reference the actual agents in .bmad/
+    const agentGen = new AgentCommandGenerator(this.bmadFolderName);
+    const { artifacts: agentArtifacts, counts: agentCounts } = await agentGen.collectAgentArtifacts(bmadDir, options.selectedModules || []);
+
+    // Write agent launcher files with FLATTENED naming
+    // Antigravity ignores directory structure, so we flatten to: bmad-module-agents-name.md
+    // This creates slash commands like /bmad-bmm-agents-dev instead of /dev
+    let agentCount = 0;
+    for (const artifact of agentArtifacts) {
+      const flattenedName = this.flattenFilename(artifact.relativePath);
+      const targetPath = path.join(bmadWorkflowsDir, flattenedName);
+      await this.writeFile(targetPath, artifact.content);
+      agentCount++;
+    }
+
+    // Process Antigravity specific injections for installed modules
+    // Use pre-collected configuration if available, or skip if already configured
+    if (options.preCollectedConfig && options.preCollectedConfig._alreadyConfigured) {
+      // IDE is already configured from previous installation, skip prompting
+      // Just process with default/existing configuration
+      await this.processModuleInjectionsWithConfig(projectDir, bmadDir, options, {});
+    } else if (options.preCollectedConfig) {
+      await this.processModuleInjectionsWithConfig(projectDir, bmadDir, options, options.preCollectedConfig);
+    } else {
+      await this.processModuleInjections(projectDir, bmadDir, options);
+    }
+
+    // Generate workflow commands from manifest (if it exists)
+    const workflowGen = new WorkflowCommandGenerator(this.bmadFolderName);
+    const { artifacts: workflowArtifacts } = await workflowGen.collectWorkflowArtifacts(bmadDir);
+
+    // Write workflow-command artifacts with FLATTENED naming
+    let workflowCommandCount = 0;
+    for (const artifact of workflowArtifacts) {
+      if (artifact.type === 'workflow-command') {
+        const flattenedName = this.flattenFilename(artifact.relativePath);
+        const targetPath = path.join(bmadWorkflowsDir, flattenedName);
+        await this.writeFile(targetPath, artifact.content);
+        workflowCommandCount++;
+      }
+    }
+
+    // Generate task and tool commands from manifests (if they exist)
+    const taskToolGen = new TaskToolCommandGenerator();
+    const taskToolResult = await taskToolGen.generateTaskToolCommands(projectDir, bmadDir);
+
+    console.log(chalk.green(`✓ ${this.name} configured:`));
+    console.log(chalk.dim(`  - ${agentCount} agents installed`));
+    if (workflowCommandCount > 0) {
+      console.log(chalk.dim(`  - ${workflowCommandCount} workflow commands generated`));
+    }
+    if (taskToolResult.generated > 0) {
+      console.log(
+        chalk.dim(
+          `  - ${taskToolResult.generated} task/tool commands generated (${taskToolResult.tasks} tasks, ${taskToolResult.tools} tools)`,
+        ),
+      );
+    }
+    console.log(chalk.dim(`  - Workflows directory: ${path.relative(projectDir, bmadWorkflowsDir)}`));
+    console.log(chalk.yellow(`\n  Note: Antigravity uses flattened slash commands (e.g., /bmad-module-agents-name)`));
+
+    return {
+      success: true,
+      agents: agentCount,
+    };
+  }
+
+  /**
+   * Read and process file content
+   */
+  async readAndProcess(filePath, metadata) {
+    const fs = require('fs-extra');
+    const content = await fs.readFile(filePath, 'utf8');
+    return this.processContent(content, metadata);
+  }
+
+  /**
+   * Override processContent to keep {project-root} placeholder
+   */
+  processContent(content, metadata = {}) {
+    // Use the base class method WITHOUT projectDir to preserve {project-root} placeholder
+    return super.processContent(content, metadata);
+  }
+
+  /**
+   * Get agents from source modules (not installed location)
+   */
+  async getAgentsFromSource(sourceDir, selectedModules) {
+    const fs = require('fs-extra');
+    const agents = [];
+
+    // Add core agents
+    const corePath = getModulePath('core');
+    if (await fs.pathExists(path.join(corePath, 'agents'))) {
+      const coreAgents = await getAgentsFromDir(path.join(corePath, 'agents'), 'core');
+      agents.push(...coreAgents);
+    }
+
+    // Add module agents
+    for (const moduleName of selectedModules) {
+      const modulePath = path.join(sourceDir, moduleName);
+      const agentsPath = path.join(modulePath, 'agents');
+
+      if (await fs.pathExists(agentsPath)) {
+        const moduleAgents = await getAgentsFromDir(agentsPath, moduleName);
+        agents.push(...moduleAgents);
+      }
+    }
+
+    return agents;
+  }
+
+  /**
+   * Process module injections with pre-collected configuration
+   */
+  async processModuleInjectionsWithConfig(projectDir, bmadDir, options, preCollectedConfig) {
+    // Get list of installed modules
+    const modules = options.selectedModules || [];
+    const { subagentChoices, installLocation } = preCollectedConfig;
+
+    // Get the actual source directory (not the installation directory)
+    await this.processModuleInjectionsInternal({
+      projectDir,
+      modules,
+      handler: 'antigravity',
+      subagentChoices,
+      installLocation,
+      interactive: false,
+    });
+  }
+
+  /**
+   * Process Antigravity specific injections for installed modules
+   * Looks for injections.yaml in each module's antigravity sub-module
+   */
+  async processModuleInjections(projectDir, bmadDir, options) {
+    // Get list of installed modules
+    const modules = options.selectedModules || [];
+    let subagentChoices = null;
+    let installLocation = null;
+
+    // Get the actual source directory (not the installation directory)
+    const { subagentChoices: updatedChoices, installLocation: updatedLocation } = await this.processModuleInjectionsInternal({
+      projectDir,
+      modules,
+      handler: 'antigravity',
+      subagentChoices,
+      installLocation,
+      interactive: true,
+    });
+
+    if (updatedChoices) {
+      subagentChoices = updatedChoices;
+    }
+    if (updatedLocation) {
+      installLocation = updatedLocation;
+    }
+  }
+
+  async processModuleInjectionsInternal({ projectDir, modules, handler, subagentChoices, installLocation, interactive = false }) {
+    let choices = subagentChoices;
+    let location = installLocation;
+
+    for (const moduleName of modules) {
+      const configData = await loadModuleInjectionConfig(handler, moduleName);
+
+      if (!configData) {
+        continue;
+      }
+
+      const { config, handlerBaseDir } = configData;
+
+      if (interactive) {
+        console.log(chalk.cyan(`\nConfiguring ${moduleName} ${handler} features...`));
+      }
+
+      if (interactive && config.subagents && !choices) {
+        choices = await this.promptSubagentInstallation(config.subagents);
+
+        if (choices.install !== 'none') {
+          const inquirer = require('inquirer');
+          const locationAnswer = await inquirer.prompt([
+            {
+              type: 'list',
+              name: 'location',
+              message: 'Where would you like to install Antigravity subagents?',
+              choices: [
+                { name: 'Project level (.agent/agents/)', value: 'project' },
+                { name: 'User level (~/.agent/agents/)', value: 'user' },
+              ],
+              default: 'project',
+            },
+          ]);
+          location = locationAnswer.location;
+        }
+      }
+
+      if (config.injections && choices && choices.install !== 'none') {
+        for (const injection of config.injections) {
+          if (shouldApplyInjection(injection, choices)) {
+            await this.injectContent(projectDir, injection, choices);
+          }
+        }
+      }
+
+      if (config.subagents && choices && choices.install !== 'none') {
+        await this.copySelectedSubagents(projectDir, handlerBaseDir, config.subagents, choices, location || 'project');
+      }
+    }
+
+    return { subagentChoices: choices, installLocation: location };
+  }
+
+  /**
+   * Prompt user for subagent installation preferences
+   */
+  async promptSubagentInstallation(subagentConfig) {
+    const inquirer = require('inquirer');
+
+    // First ask if they want to install subagents
+    const { install } = await inquirer.prompt([
+      {
+        type: 'list',
+        name: 'install',
+        message: 'Would you like to install Antigravity subagents for enhanced functionality?',
+        choices: [
+          { name: 'Yes, install all subagents', value: 'all' },
+          { name: 'Yes, let me choose specific subagents', value: 'selective' },
+          { name: 'No, skip subagent installation', value: 'none' },
+        ],
+        default: 'all',
+      },
+    ]);
+
+    if (install === 'selective') {
+      // Show list of available subagents with descriptions
+      const subagentInfo = {
+        'market-researcher.md': 'Market research and competitive analysis',
+        'requirements-analyst.md': 'Requirements extraction and validation',
+        'technical-evaluator.md': 'Technology stack evaluation',
+        'epic-optimizer.md': 'Epic and story breakdown optimization',
+        'document-reviewer.md': 'Document quality review',
+      };
+
+      const { selected } = await inquirer.prompt([
+        {
+          type: 'checkbox',
+          name: 'selected',
+          message: 'Select subagents to install:',
+          choices: subagentConfig.files.map((file) => ({
+            name: `${file.replace('.md', '')} - ${subagentInfo[file] || 'Specialized assistant'}`,
+            value: file,
+            checked: true,
+          })),
+        },
+      ]);
+
+      return { install: 'selective', selected };
+    }
+
+    return { install };
+  }
+
+  /**
+   * Inject content at specified point in file
+   */
+  async injectContent(projectDir, injection, subagentChoices = null) {
+    const fs = require('fs-extra');
+    const targetPath = path.join(projectDir, injection.file);
+
+    if (await this.exists(targetPath)) {
+      let content = await fs.readFile(targetPath, 'utf8');
+      const marker = `<!-- IDE-INJECT-POINT: ${injection.point} -->`;
+
+      if (content.includes(marker)) {
+        let injectionContent = injection.content;
+
+        // Filter content if selective subagents chosen
+        if (subagentChoices && subagentChoices.install === 'selective' && injection.point === 'pm-agent-instructions') {
+          injectionContent = filterAgentInstructions(injection.content, subagentChoices.selected);
+        }
+
+        content = content.replace(marker, injectionContent);
+        await fs.writeFile(targetPath, content);
+        console.log(chalk.dim(`    Injected: ${injection.point} → ${injection.file}`));
+      }
+    }
+  }
+
+  /**
+   * Copy selected subagents to appropriate Antigravity agents directory
+   */
+  async copySelectedSubagents(projectDir, handlerBaseDir, subagentConfig, choices, location) {
+    const fs = require('fs-extra');
+    const os = require('node:os');
+
+    // Determine target directory based on user choice
+    let targetDir;
+    if (location === 'user') {
+      targetDir = path.join(os.homedir(), '.agent', 'agents');
+      console.log(chalk.dim(`  Installing subagents globally to: ~/.agent/agents/`));
+    } else {
+      targetDir = path.join(projectDir, '.agent', 'agents');
+      console.log(chalk.dim(`  Installing subagents to project: .agent/agents/`));
+    }
+
+    // Ensure target directory exists
+    await this.ensureDir(targetDir);
+
+    const resolvedFiles = await resolveSubagentFiles(handlerBaseDir, subagentConfig, choices);
+
+    let copiedCount = 0;
+    for (const resolved of resolvedFiles) {
+      try {
+        const sourcePath = resolved.absolutePath;
+
+        const subFolder = path.dirname(resolved.relativePath);
+        let targetPath;
+        if (subFolder && subFolder !== '.') {
+          const targetSubDir = path.join(targetDir, subFolder);
+          await this.ensureDir(targetSubDir);
+          targetPath = path.join(targetSubDir, path.basename(resolved.file));
+        } else {
+          targetPath = path.join(targetDir, path.basename(resolved.file));
+        }
+
+        await fs.copyFile(sourcePath, targetPath);
+        console.log(chalk.green(`    ✓ Installed: ${subFolder === '.' ? '' : `${subFolder}/`}${path.basename(resolved.file, '.md')}`));
+        copiedCount++;
+      } catch (error) {
+        console.log(chalk.yellow(`    ⚠ Error copying ${resolved.file}: ${error.message}`));
+      }
+    }
+
+    if (copiedCount > 0) {
+      console.log(chalk.dim(`  Total subagents installed: ${copiedCount}`));
+    }
+  }
+}
+
+module.exports = { AntigravitySetup };
diff --git a/tools/cli/installers/lib/ide/codex.js b/tools/cli/installers/lib/ide/codex.js
index 66a00327..480d805c 100644
--- a/tools/cli/installers/lib/ide/codex.js
+++ b/tools/cli/installers/lib/ide/codex.js
@@ -212,11 +212,6 @@ class CodexSetup extends BaseIdeSetup {
     return path.join(os.homedir(), '.codex', 'prompts');
   }
 
-  flattenFilename(relativePath) {
-    const sanitized = relativePath.replaceAll(/[\\/]/g, '-');
-    return `bmad-${sanitized}`;
-  }
-
   async flattenAndWriteArtifacts(artifacts, destDir) {
     let written = 0;