diff --git a/src/cli.ts b/src/cli.ts
index 6f249a3e..03883bc3 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -631,11 +631,16 @@ program
   .alias('check-deps')
   .description('Check Codeman tool dependencies (Node, Claude CLI, tmux, LibreOffice, MS Office)')
   .option('--json', 'Output structured JSON instead of a table')
-  .option('--category <name>', 'Only check one category (core|office|documents|media|other)')
+  .option('--category <name>', 'Only check one category (core|office|other)')
   .action(async (options) => {
     const { createRealHost, checkAll } = await import('./utils/dependency-checker.js');
     const { renderTable, renderJson, computeExitCode } = await import('./utils/dependency-report.js');
-    const { DEPENDENCY_REGISTRY } = await import('./config/dependency-registry.js');
+    const { DEPENDENCY_REGISTRY, TOOL_CATEGORIES } = await import('./config/dependency-registry.js');
+
+    if (options.category && !(TOOL_CATEGORIES as readonly string[]).includes(options.category)) {
+      console.error(`Unknown category "${options.category}". Valid categories: ${TOOL_CATEGORIES.join(', ')}`);
+      process.exit(2);
+    }
 
     const host = createRealHost();
     const registry = options.category
diff --git a/src/config/dependency-registry.ts b/src/config/dependency-registry.ts
index 2e4a6220..bc04c485 100644
--- a/src/config/dependency-registry.ts
+++ b/src/config/dependency-registry.ts
@@ -8,7 +8,11 @@
  */
 
 export type ProbeEnvironment = 'linux' | 'darwin' | 'win32' | 'wsl';
-export type ToolCategory = 'core' | 'office' | 'other';
+
+/** The valid `--category` filter values; single source of truth for the type, the CLI
+ *  help text, and CLI input validation. */
+export const TOOL_CATEGORIES = ['core', 'office', 'other'] as const;
+export type ToolCategory = (typeof TOOL_CATEGORIES)[number];
 
 /** Resolve a binary on the PATH and read its version. */
 export interface PathResolver {
@@ -49,7 +53,7 @@ export const DEPENDENCY_REGISTRY: ToolDependency[] = [
     label: 'Node.js',
     category: 'core',
     required: true,
-    minVersion: '18.0.0',
+    minVersion: '22.0.0',
     resolvers: [{ match: ALL, resolver: { kind: 'path', bins: ['node'], versionArg: '--version' } }],
     installHint: { linux: 'https://nodejs.org', darwin: 'brew install node', wsl: 'https://nodejs.org' },
   },
@@ -86,14 +90,6 @@ export const DEPENDENCY_REGISTRY: ToolDependency[] = [
     usedBy: ['Codex sessions'],
     resolvers: [{ match: ALL, resolver: { kind: 'path', bins: ['codex'], versionArg: '--version' } }],
   },
-  {
-    id: 'gemini',
-    label: 'Gemini CLI',
-    category: 'core',
-    required: false,
-    usedBy: ['Gemini sessions'],
-    resolvers: [{ match: ALL, resolver: { kind: 'path', bins: ['gemini'], versionArg: '--version' } }],
-  },
   {
     id: 'libreoffice',
     label: 'LibreOffice',
@@ -108,6 +104,22 @@ export const DEPENDENCY_REGISTRY: ToolDependency[] = [
     ],
     installHint: { linux: 'sudo apt install libreoffice', darwin: 'brew install --cask libreoffice' },
   },
+  {
+    id: 'pdftoppm',
+    label: 'pdftoppm',
+    category: 'office',
+    required: false,
+    usedBy: ['document preview', 'PDF/Office first-page thumbnails'],
+    // poppler's pdftoppm prints its version to stderr; presence is what matters here.
+    resolvers: [
+      { match: ['linux', 'darwin', 'wsl'], resolver: { kind: 'path', bins: ['pdftoppm'], versionArg: '-v' } },
+    ],
+    installHint: {
+      linux: 'sudo apt install poppler-utils',
+      darwin: 'brew install poppler',
+      wsl: 'sudo apt install poppler-utils',
+    },
+  },
   {
     id: 'msoffice',
     label: 'MS Office',
diff --git a/test/dependency-checker.test.ts b/test/dependency-checker.test.ts
index cc82966c..b3bb5573 100644
--- a/test/dependency-checker.test.ts
+++ b/test/dependency-checker.test.ts
@@ -22,8 +22,8 @@ describe('DEPENDENCY_REGISTRY', () => {
       .map((t) => t.id)
       .sort();
     expect(required).toEqual(['node', 'tmux']);
-    // all four agent CLIs are optional (Codeman runs any of them)
-    const agentClis = ['claude', 'opencode', 'codex', 'gemini'];
+    // all agent CLIs are optional (Codeman runs any of them)
+    const agentClis = ['claude', 'opencode', 'codex'];
     expect(DEPENDENCY_REGISTRY.filter((t) => agentClis.includes(t.id)).every((t) => t.required === false)).toBe(true);
     const office = DEPENDENCY_REGISTRY.filter((t) => t.category === 'office');
     expect(office.every((t) => t.required === false)).toBe(true);