feat(gemini): add Gemini CLI as sixth target provider

Add `--to gemini` support for both `convert` and `install` commands,
converting Claude Code plugins into Gemini CLI-compatible format.

- Agents convert to `.gemini/skills/*/SKILL.md` with description frontmatter
- Commands convert to `.gemini/commands/*.toml` with TOML prompt format
- Namespaced commands create directory structure (workflows:plan -> workflows/plan.toml)
- Skills pass through unchanged (identical SKILL.md standard)
- MCP servers written to `.gemini/settings.json` with merge support
- Content transforms: .claude/ paths, Task calls, @agent references
- Hooks emit warning (different format in Gemini)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/targets/gemini.ts

@@ -0,0 +1,65 @@
+import path from "path"
+import { backupFile, copyDir, ensureDir, pathExists, readJson, writeJson, writeText } from "../utils/files"
+import type { GeminiBundle } from "../types/gemini"
+
+export async function writeGeminiBundle(outputRoot: string, bundle: GeminiBundle): Promise<void> {
+  const paths = resolveGeminiPaths(outputRoot)
+  await ensureDir(paths.geminiDir)
+
+  if (bundle.generatedSkills.length > 0) {
+    for (const skill of bundle.generatedSkills) {
+      await writeText(path.join(paths.skillsDir, skill.name, "SKILL.md"), skill.content + "\n")
+    }
+  }
+
+  if (bundle.skillDirs.length > 0) {
+    for (const skill of bundle.skillDirs) {
+      await copyDir(skill.sourceDir, path.join(paths.skillsDir, skill.name))
+    }
+  }
+
+  if (bundle.commands.length > 0) {
+    for (const command of bundle.commands) {
+      await writeText(path.join(paths.commandsDir, `${command.name}.toml`), command.content + "\n")
+    }
+  }
+
+  if (bundle.mcpServers && Object.keys(bundle.mcpServers).length > 0) {
+    const settingsPath = path.join(paths.geminiDir, "settings.json")
+    const backupPath = await backupFile(settingsPath)
+    if (backupPath) {
+      console.log(`Backed up existing settings.json to ${backupPath}`)
+    }
+
+    // Merge mcpServers into existing settings if present
+    let existingSettings: Record<string, unknown> = {}
+    if (await pathExists(settingsPath)) {
+      try {
+        existingSettings = await readJson<Record<string, unknown>>(settingsPath)
+      } catch {
+        // If existing file is invalid JSON, start fresh
+      }
+    }
+
+    const merged = { ...existingSettings, mcpServers: bundle.mcpServers }
+    await writeJson(settingsPath, merged)
+  }
+}
+
+function resolveGeminiPaths(outputRoot: string) {
+  const base = path.basename(outputRoot)
+  // If already pointing at .gemini, write directly into it
+  if (base === ".gemini") {
+    return {
+      geminiDir: outputRoot,
+      skillsDir: path.join(outputRoot, "skills"),
+      commandsDir: path.join(outputRoot, "commands"),
+    }
+  }
+  // Otherwise nest under .gemini
+  return {
+    geminiDir: path.join(outputRoot, ".gemini"),
+    skillsDir: path.join(outputRoot, ".gemini", "skills"),
+    commandsDir: path.join(outputRoot, ".gemini", "commands"),
+  }
+}

src/targets/index.ts

@@ -4,16 +4,19 @@ import type { CodexBundle } from "../types/codex"
 import type { DroidBundle } from "../types/droid"
 import type { CursorBundle } from "../types/cursor"
 import type { PiBundle } from "../types/pi"
+import type { GeminiBundle } from "../types/gemini"
 import { convertClaudeToOpenCode, type ClaudeToOpenCodeOptions } from "../converters/claude-to-opencode"
 import { convertClaudeToCodex } from "../converters/claude-to-codex"
 import { convertClaudeToDroid } from "../converters/claude-to-droid"
 import { convertClaudeToCursor } from "../converters/claude-to-cursor"
 import { convertClaudeToPi } from "../converters/claude-to-pi"
+import { convertClaudeToGemini } from "../converters/claude-to-gemini"
 import { writeOpenCodeBundle } from "./opencode"
 import { writeCodexBundle } from "./codex"
 import { writeDroidBundle } from "./droid"
 import { writeCursorBundle } from "./cursor"
 import { writePiBundle } from "./pi"
+import { writeGeminiBundle } from "./gemini"
 
 export type TargetHandler<TBundle = unknown> = {
   name: string
@@ -53,4 +56,10 @@ export const targets: Record<string, TargetHandler> = {
     convert: convertClaudeToPi as TargetHandler<PiBundle>["convert"],
     write: writePiBundle as TargetHandler<PiBundle>["write"],
   },
+  gemini: {
+    name: "gemini",
+    implemented: true,
+    convert: convertClaudeToGemini as TargetHandler<GeminiBundle>["convert"],
+    write: writeGeminiBundle as TargetHandler<GeminiBundle>["write"],
+  },
 }