diff --git a/src/mux-interface.ts b/src/mux-interface.ts
index 1eddd1da..9bc7dfec 100644
--- a/src/mux-interface.ts
+++ b/src/mux-interface.ts
@@ -16,6 +16,7 @@ import type {
   OpenCodeConfig,
   CodexConfig,
   EffortLevel,
+  GeminiConfig,
 } from './types.js';
 
 /**
@@ -64,6 +65,7 @@ export interface CreateSessionOptions {
   allowedTools?: string;
   openCodeConfig?: OpenCodeConfig;
   codexConfig?: CodexConfig;
+  geminiConfig?: GeminiConfig;
   /** When restoring after reboot, resume a previous Claude conversation by its session ID */
   resumeSessionId?: string;
   /** Extra env vars exported before launching the CLI (e.g., CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS). Ephemeral — not written to disk. */
@@ -83,6 +85,7 @@ export interface RespawnPaneOptions {
   allowedTools?: string;
   openCodeConfig?: OpenCodeConfig;
   codexConfig?: CodexConfig;
+  geminiConfig?: GeminiConfig;
   /** Resume a previous Claude conversation when respawning */
   resumeSessionId?: string;
   /** Extra env vars exported before launching the CLI (preserved across respawns). */
diff --git a/src/session.ts b/src/session.ts
index a6281069..3b45835d 100644
--- a/src/session.ts
+++ b/src/session.ts
@@ -48,6 +48,7 @@ import {
   type OpenCodeConfig,
   type CodexConfig,
   type EffortLevel,
+  type GeminiConfig,
 } from './types.js';
 import type { TerminalMultiplexer, MuxSession } from './mux-interface.js';
 import { TaskTracker, type BackgroundTask } from './task-tracker.js';
@@ -133,7 +134,22 @@ const NEWLINE_SPLIT_PATTERN = /\r?\n/;
 
 /** True for external-CLI run modes (non-Claude) that use their own TUI and output format. */
 export function isExternalCliMode(mode: SessionMode): boolean {
-  return mode === 'opencode' || mode === 'codex';
+  return mode === 'opencode' || mode === 'codex' || mode === 'gemini';
+}
+
+function getModeLabel(mode: SessionMode): string {
+  switch (mode) {
+    case 'opencode':
+      return 'OpenCode';
+    case 'codex':
+      return 'Codex';
+    case 'gemini':
+      return 'Gemini';
+    case 'shell':
+      return 'Shell';
+    case 'claude':
+      return 'Claude';
+  }
 }
 
 /**
@@ -351,6 +367,8 @@ export class Session extends EventEmitter {
   private _openCodeConfig: OpenCodeConfig | undefined;
   // Codex configuration (only for mode === 'codex')
   private _codexConfig: CodexConfig | undefined;
+  // Gemini configuration (only for mode === 'gemini')
+  private _geminiConfig: GeminiConfig | undefined;
   private _resumeSessionId: string | undefined;
 
   // Ephemeral env overrides (e.g., CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS). Exported by tmux
@@ -421,6 +439,8 @@ export class Session extends EventEmitter {
       openCodeConfig?: OpenCodeConfig;
       /** Codex configuration (only for mode === 'codex') */
       codexConfig?: CodexConfig;
+      /** Gemini configuration (only for mode === 'gemini') */
+      geminiConfig?: GeminiConfig;
       /** Resume a previous Claude conversation (used after server reboot) */
       resumeSessionId?: string;
       /** Extra env vars exported to the CLI at spawn time (no disk persistence) */
@@ -481,6 +501,11 @@ export class Session extends EventEmitter {
       this._codexConfig = config.codexConfig;
     }
 
+    // Apply Gemini configuration
+    if (config.geminiConfig) {
+      this._geminiConfig = config.geminiConfig;
+    }
+
     // Apply env overrides (exported at spawn, not persisted to disk).
     // Legacy migration: pre-0.7.2 carried effort as the CLAUDE_CODE_EFFORT_LEVEL env var,
     // which hard-locks /effort switching. Extract it into _effort (--settings soft default)
@@ -985,6 +1010,7 @@ export class Session extends EventEmitter {
       cliLatestVersion: this._cliLatestVersion || undefined,
       openCodeConfig: this._openCodeConfig,
       codexConfig: this._codexConfig,
+      geminiConfig: this._geminiConfig,
       resumeSessionId: this._resumeSessionId,
       effort: this._effort,
       attachmentHistory: this.attachmentHistory.length > 0 ? this.attachmentHistory : undefined,
@@ -1224,7 +1250,7 @@ export class Session extends EventEmitter {
 
     this._resetBuffers();
 
-    const modeLabel = this.mode === 'opencode' ? 'OpenCode' : this.mode === 'codex' ? 'Codex' : 'Claude';
+    const modeLabel = getModeLabel(this.mode);
     console.log(
       `[Session] Starting interactive ${modeLabel} session` + (this._useMux ? ` (with ${this._mux!.backend})` : '')
     );
@@ -1243,6 +1269,7 @@ export class Session extends EventEmitter {
             allowedTools: this._allowedTools,
             openCodeConfig: this._openCodeConfig,
             codexConfig: this._codexConfig,
+            geminiConfig: this._geminiConfig,
             resumeSessionId: this._resumeSessionId,
             envOverrides: this._envOverrides,
             effort: this._effort,
@@ -1258,6 +1285,7 @@ export class Session extends EventEmitter {
             allowedTools: this._allowedTools,
             openCodeConfig: this._openCodeConfig,
             codexConfig: this._codexConfig,
+            geminiConfig: this._geminiConfig,
             resumeSessionId: this._resumeSessionId,
             envOverrides: this._envOverrides,
             effort: this._effort,
@@ -1331,6 +1359,10 @@ export class Session extends EventEmitter {
       if (this.mode === 'codex') {
         throw new Error('Codex sessions require tmux. Direct PTY fallback is not supported.');
       }
+      // Gemini sessions require tmux for Gemini/Google auth env injection via setenv
+      if (this.mode === 'gemini') {
+        throw new Error('Gemini sessions require tmux. Direct PTY fallback is not supported.');
+      }
       try {
         // Pass --session-id to use the SAME ID as the Codeman session
         // This ensures subagents can be directly matched to the correct tab
diff --git a/src/tmux-manager.ts b/src/tmux-manager.ts
index 74987265..6e288055 100644
--- a/src/tmux-manager.ts
+++ b/src/tmux-manager.ts
@@ -41,9 +41,17 @@ import {
   type OpenCodeConfig,
   type CodexConfig,
   type EffortLevel,
+  type GeminiConfig,
 } from './types.js';
 import { buildEffortCliArgs } from './session-cli-builder.js';
-import { wrapWithNice, SAFE_PATH_PATTERN, findClaudeDir, resolveOpenCodeDir, resolveCodexDir } from './utils/index.js';
+import {
+  wrapWithNice,
+  SAFE_PATH_PATTERN,
+  findClaudeDir,
+  resolveOpenCodeDir,
+  resolveCodexDir,
+  resolveGeminiDir,
+} from './utils/index.js';
 import type {
   TerminalMultiplexer,
   MuxSession,
@@ -571,6 +579,35 @@ export function buildCodexCommand(config?: CodexConfig): string {
   return parts.join(' ');
 }
 
+/**
+ * Build the Gemini CLI command with appropriate flags.
+ *
+ * `--skip-trust` avoids a first-run workspace trust prompt inside Codeman.
+ * Approval mode defaults to `yolo` for parity with Codeman's Claude default
+ * of `--dangerously-skip-permissions`; users can override it later through
+ * Gemini config once Codeman exposes richer Gemini settings.
+ */
+function buildGeminiCommand(config?: GeminiConfig): string {
+  const parts = ['gemini', '--skip-trust'];
+
+  const approvalMode = config?.approvalMode || 'yolo';
+  if (['default', 'auto_edit', 'yolo', 'plan'].includes(approvalMode)) {
+    parts.push('--approval-mode', approvalMode);
+  }
+
+  if (config?.model) {
+    const safeModel = /^[a-zA-Z0-9._\-/]+$/.test(config.model) ? config.model : undefined;
+    if (safeModel) parts.push('--model', safeModel);
+  }
+
+  if (config?.resumeSession) {
+    const safeId = /^[a-zA-Z0-9._-]+$/.test(config.resumeSession) ? config.resumeSession : undefined;
+    if (safeId) parts.push('--resume', safeId);
+  }
+
+  return parts.join(' ');
+}
+
 /**
  * Build the spawn command for any session mode.
  * Shared by createSession() and respawnPane() to avoid duplication.
@@ -597,6 +634,7 @@ function buildSpawnCommand(options: {
   allowedTools?: string;
   openCodeConfig?: OpenCodeConfig;
   codexConfig?: CodexConfig;
+  geminiConfig?: GeminiConfig;
   resumeSessionId?: string;
   effort?: EffortLevel;
 }): string {
@@ -624,6 +662,9 @@ function buildSpawnCommand(options: {
   if (options.mode === 'codex') {
     return buildCodexCommand(options.codexConfig);
   }
+  if (options.mode === 'gemini') {
+    return buildGeminiCommand(options.geminiConfig);
+  }
   return '$SHELL';
 }
 
@@ -674,6 +715,38 @@ function setCodexEnvVars(tmuxCmd: string, muxName: string): void {
   }
 }
 
+/**
+ * Set sensitive environment variables for Gemini on a tmux session via setenv.
+ * Gemini Pro/Ultra users usually authenticate via cached Google login; these
+ * variables cover API-key and Vertex AI paths without putting secrets in ps.
+ */
+function setGeminiEnvVars(muxName: string): void {
+  const sensitiveVars = [
+    'GEMINI_API_KEY',
+    'GEMINI_MODEL',
+    'GOOGLE_API_KEY',
+    'GOOGLE_CLOUD_PROJECT',
+    'GOOGLE_CLOUD_LOCATION',
+    'GOOGLE_APPLICATION_CREDENTIALS',
+    'GOOGLE_GENAI_USE_VERTEXAI',
+  ];
+  for (const key of sensitiveVars) {
+    const val = process.env[key];
+    if (val) {
+      const escaped = val.replace(/'/g, "'\\''");
+      try {
+        execSync(`tmux setenv -t '${muxName}' ${key} '${escaped}'`, {
+          encoding: 'utf8',
+          timeout: EXEC_TIMEOUT_MS,
+          stdio: ['pipe', 'pipe', 'pipe'],
+        });
+      } catch {
+        /* Non-critical — key may not be needed */
+      }
+    }
+  }
+}
+
 /**
  * Set OPENCODE_CONFIG_CONTENT on a tmux session via setenv.
  * Uses tmux setenv to avoid shell metacharacter injection from user-supplied JSON.
@@ -930,6 +1003,10 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
       const dir = resolveCodexDir();
       return { pathExport: dir ? `export PATH="${dir}:$PATH" && ` : '', dir };
     }
+    if (mode === 'gemini') {
+      const dir = resolveGeminiDir();
+      return { pathExport: dir ? `export PATH="${dir}:$PATH" && ` : '', dir };
+    }
     return { pathExport: '', dir: null };
   }
 
@@ -953,6 +1030,13 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
     setCodexEnvVars(this.tmux(), muxName);
   }
 
+  /**
+   * Configure Gemini-specific environment on a tmux session.
+   */
+  private _configureGemini(muxName: string): void {
+    setGeminiEnvVars(muxName);
+  }
+
   /**
    * Creates a new tmux session wrapping Claude CLI or a shell.
    * In test mode: creates an in-memory session only (no real tmux session).
@@ -969,6 +1053,7 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
       allowedTools,
       openCodeConfig,
       codexConfig,
+      geminiConfig,
       resumeSessionId,
       envOverrides,
       effort,
@@ -1007,6 +1092,12 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
     if (mode === 'opencode' && !cliDir) {
       throw new Error('OpenCode CLI not found. Install with: curl -fsSL https://opencode.ai/install | bash');
     }
+    if (mode === 'codex' && !cliDir) {
+      throw new Error('Codex CLI not found. Install with: npm install -g @openai/codex');
+    }
+    if (mode === 'gemini' && !cliDir) {
+      throw new Error('Gemini CLI not found. Install with: npm install -g @google/gemini-cli');
+    }
 
     const envExportsStr = this.buildEnvExports(sessionId, muxName, mode).join(' && ');
 
@@ -1018,6 +1109,7 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
       allowedTools,
       openCodeConfig,
       codexConfig,
+      geminiConfig,
       resumeSessionId,
       effort,
     });
@@ -1067,6 +1159,10 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
       } else if (mode === 'codex') {
         this._configureCodex(muxName);
       }
+      // For Gemini: set Gemini/Google auth env vars via tmux setenv
+      if (mode === 'gemini') {
+        this._configureGemini(muxName);
+      }
 
       // Apply user-supplied env overrides (e.g., CLAUDE_CODE_EFFORT_LEVEL) via tmux setenv
       // so secret values stay off the bash command line. Must run before respawn-pane.
@@ -1224,6 +1320,7 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
       allowedTools,
       openCodeConfig,
       codexConfig,
+      geminiConfig,
       resumeSessionId,
       envOverrides,
       effort,
@@ -1247,6 +1344,7 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
       allowedTools,
       openCodeConfig,
       codexConfig,
+      geminiConfig,
       resumeSessionId,
       effort,
     });
@@ -1261,6 +1359,10 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
       } else if (mode === 'codex') {
         this._configureCodex(muxName);
       }
+      // For Gemini: set Gemini/Google auth env vars via tmux setenv before respawn
+      if (mode === 'gemini') {
+        this._configureGemini(muxName);
+      }
 
       // Re-apply user env overrides before respawn so the new shell inherits them.
       this.applyEnvOverrides(muxName, envOverrides);
diff --git a/src/types/session.ts b/src/types/session.ts
index 4cf742d9..460f6e67 100644
--- a/src/types/session.ts
+++ b/src/types/session.ts
@@ -8,10 +8,12 @@
  * - SessionConfig — creation-time config (id, workingDir, createdAt)
  * - SessionOutput — captured stdout/stderr/exitCode
  * - SessionStatus — 'idle' | 'busy' | 'stopped' | 'error'
- * - SessionMode — 'claude' | 'shell' | 'opencode' | 'codex' (which CLI backend)
+ * - SessionMode — 'claude' | 'shell' | 'opencode' | 'codex' | 'gemini' (which CLI backend)
  * - ClaudeMode — CLI permission mode ('dangerously-skip-permissions' | 'normal' | 'allowedTools')
  * - SessionColor — visual differentiation color
  * - OpenCodeConfig — OpenCode-specific settings (model, autoAllowTools, continueSession)
+ * - CodexConfig — Codex (OpenAI CLI)-specific settings (model, resumeSessionId)
+ * - GeminiConfig — Gemini CLI-specific settings (model, approvalMode, resumeSession)
  *
  * Cross-domain relationships:
  * - SessionState.respawnConfig embeds RespawnConfig (respawn domain)
@@ -39,7 +41,7 @@ export type SessionStatus = 'idle' | 'busy' | 'stopped' | 'error';
 export type ClaudeMode = 'dangerously-skip-permissions' | 'normal' | 'allowedTools';
 
 /** Session mode: which CLI backend a session runs */
-export type SessionMode = 'claude' | 'shell' | 'opencode' | 'codex';
+export type SessionMode = 'claude' | 'shell' | 'opencode' | 'codex' | 'gemini';
 
 /**
  * Valid Claude CLI effort levels (claude >= 2.1.154).
@@ -85,6 +87,16 @@ export interface CodexConfig {
   renderMode?: CodexRenderMode;
 }
 
+/** Gemini CLI session configuration */
+export interface GeminiConfig {
+  /** Model identifier (e.g., "gemini-2.5-pro"). Passed via --model. */
+  model?: string;
+  /** Gemini approval mode for tool calls. */
+  approvalMode?: 'default' | 'auto_edit' | 'yolo' | 'plan';
+  /** Resume a previous Gemini session ("latest", index, or session id). */
+  resumeSession?: string;
+}
+
 /**
  * Configuration for creating a new session
  */
@@ -214,6 +226,8 @@ export interface SessionState {
   openCodeConfig?: OpenCodeConfig;
   /** Codex-specific configuration (only for mode === 'codex') */
   codexConfig?: CodexConfig;
+  /** Gemini-specific configuration (only for mode === 'gemini') */
+  geminiConfig?: GeminiConfig;
   /** Claude conversation session ID to resume after reboot (set by restore script) */
   resumeSessionId?: string;
   /** Claude CLI effort level (soft default via --settings, switchable in-session via /effort) */
diff --git a/src/utils/gemini-cli-resolver.ts b/src/utils/gemini-cli-resolver.ts
new file mode 100644
index 00000000..6f0b5099
--- /dev/null
+++ b/src/utils/gemini-cli-resolver.ts
@@ -0,0 +1,67 @@
+/**
+ * @fileoverview Resolve the Gemini CLI binary across common install paths.
+ *
+ * Mirrors codex-cli-resolver.ts and opencode-cli-resolver.ts. Finds the
+ * `gemini` binary and provides an augmented PATH directory for tmux sessions.
+ *
+ * @module utils/gemini-cli-resolver
+ */
+
+import { execSync } from 'node:child_process';
+import { existsSync } from 'node:fs';
+import { dirname, join } from 'node:path';
+import { homedir } from 'node:os';
+import { EXEC_TIMEOUT_MS } from '../config/exec-timeout.js';
+
+/** Common directories where the Gemini CLI binary may be installed */
+const GEMINI_SEARCH_DIRS = [
+  join(homedir(), '.gemini', 'bin'),
+  join(homedir(), '.local', 'bin'),
+  '/usr/local/bin',
+  join(homedir(), '.bun', 'bin'),
+  join(homedir(), '.npm-global', 'bin'),
+  join(homedir(), 'bin'),
+];
+
+/** Cached directory containing the gemini binary (empty string = searched but not found) */
+let _geminiDir: string | null = null;
+
+/**
+ * Finds the directory containing the `gemini` binary.
+ * Checks `which gemini` first, then falls back to common install locations.
+ *
+ * @returns Directory path, or null if not found
+ */
+export function resolveGeminiDir(): string | null {
+  if (_geminiDir !== null) return _geminiDir || null;
+
+  try {
+    const result = execSync('which gemini', {
+      encoding: 'utf-8',
+      timeout: EXEC_TIMEOUT_MS,
+    }).trim();
+    if (result && existsSync(result)) {
+      _geminiDir = dirname(result);
+      return _geminiDir;
+    }
+  } catch {
+    // Gemini not in PATH, will check common locations
+  }
+
+  for (const dir of GEMINI_SEARCH_DIRS) {
+    if (existsSync(join(dir, 'gemini'))) {
+      _geminiDir = dir;
+      return _geminiDir;
+    }
+  }
+
+  _geminiDir = '';
+  return null;
+}
+
+/**
+ * Check if Gemini CLI is available on the system.
+ */
+export function isGeminiAvailable(): boolean {
+  return resolveGeminiDir() !== null;
+}
diff --git a/src/utils/index.ts b/src/utils/index.ts
index d6e76fc5..5d7f5219 100644
--- a/src/utils/index.ts
+++ b/src/utils/index.ts
@@ -29,3 +29,4 @@ export { wrapWithNice } from './nice-wrapper.js';
 export { findClaudeDir, getAugmentedPath } from './claude-cli-resolver.js';
 export { resolveOpenCodeDir } from './opencode-cli-resolver.js';
 export { resolveCodexDir, isCodexAvailable } from './codex-cli-resolver.js';
+export { resolveGeminiDir } from './gemini-cli-resolver.js';
diff --git a/src/web/public/index.html b/src/web/public/index.html
index 4c4c7734..e5cb8048 100644
--- a/src/web/public/index.html
+++ b/src/web/public/index.html
@@ -305,6 +305,10 @@ <h1 class="welcome-title">Codeman</h1>
               <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><polygon points="5 3 19 12 5 21 5 3"/></svg>
               Run OpenCode
             </button>
+            <button class="welcome-btn welcome-btn-gemini" onclick="app.setRunMode('gemini'); app.runGemini()">
+              <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><polygon points="5 3 19 12 5 21 5 3"/></svg>
+              Run Gemini
+            </button>
           </div>
           <div class="welcome-qr" id="welcomeQr" onclick="app.toggleWelcomeQrSize()">
             <div class="welcome-qr-inner" id="welcomeQrInner"></div>
@@ -400,6 +404,9 @@ <h3 class="history-title">Resume Conversation</h3>
               <button class="run-mode-option" data-mode="codex" onclick="app.setRunMode('codex')">
                 <span class="run-mode-dot codex"></span>Codex
               </button>
+              <button class="run-mode-option" data-mode="gemini" onclick="app.setRunMode('gemini')">
+                <span class="run-mode-dot gemini"></span>Gemini
+              </button>
               <div class="run-mode-sep"></div>
               <div class="run-mode-header">Recent Sessions</div>
               <div class="run-mode-history" id="runModeHistory"></div>
diff --git a/src/web/public/mobile.css b/src/web/public/mobile.css
index e429ee0f..6b8ef7e7 100644
--- a/src/web/public/mobile.css
+++ b/src/web/public/mobile.css
@@ -777,6 +777,20 @@ html.mobile-init .file-browser-panel {
     border-color: rgba(16, 185, 129, 0.5);
   }
 
+  /* Gemini mode colors on mobile */
+  .btn-toolbar.btn-run.mode-gemini,
+  .btn-toolbar.btn-run-gear.mode-gemini {
+    background: #10243f;
+    border-color: rgba(96, 165, 250, 0.3);
+    color: #dbeafe;
+  }
+
+  .btn-toolbar.btn-run.mode-gemini:active,
+  .btn-toolbar.btn-run-gear.mode-gemini:active {
+    background: #174ea6;
+    border-color: rgba(96, 165, 250, 0.5);
+  }
+
   /* Run mode dropdown menu — positioned above toolbar on mobile */
   .run-mode-menu {
     bottom: 100%;
diff --git a/src/web/public/session-ui.js b/src/web/public/session-ui.js
index 2a2e07f7..33141854 100644
--- a/src/web/public/session-ui.js
+++ b/src/web/public/session-ui.js
@@ -1,5 +1,5 @@
 /**
- * @fileoverview Quick start (case loading, session spawning for Claude/Shell/OpenCode),
+ * @fileoverview Quick start (case loading, session spawning for Claude/Shell/OpenCode/Codex/Gemini),
  * session options modal (per-session settings, color picker, rename),
  * session options tabs (Ralph config tab), case settings (CRUD, links),
  * create case modal, and mobile case picker.
@@ -151,7 +151,7 @@ Object.assign(CodemanApp.prototype, {
     return this.run();
   },
 
-  /** Run using the selected mode (Claude Code, OpenCode, or Codex) */
+  /** Run using the selected mode (Claude Code, OpenCode, Codex, or Gemini) */
   async run() {
     const mode = this._runMode || 'claude';
     if (mode === 'opencode') {
@@ -160,6 +160,9 @@ Object.assign(CodemanApp.prototype, {
     if (mode === 'codex') {
       return this.runCodex();
     }
+    if (mode === 'gemini') {
+      return this.runGemini();
+    }
     return this.runClaude();
   },
 
@@ -257,7 +260,7 @@ Object.assign(CodemanApp.prototype, {
       gearBtn.className = `btn-toolbar btn-run-gear mode-${mode}`;
     }
     if (label) {
-      label.textContent = mode === 'opencode' ? 'Run OC' : mode === 'codex' ? 'Run CX' : 'Run';
+      label.textContent = mode === 'opencode' ? 'Run OC' : mode === 'codex' ? 'Run CX' : mode === 'gemini' ? 'Run GM' : 'Run';
     }
   },
 
@@ -640,6 +643,47 @@ Object.assign(CodemanApp.prototype, {
     }
   },
 
+  async runGemini() {
+    const caseName = document.getElementById('quickStartCase').value || 'testcase';
+
+    this.terminal.clear();
+    this.terminal.writeln(`\x1b[1;32m Starting Gemini session in ${caseName}...\x1b[0m`);
+    this.terminal.writeln('');
+    this.terminal.focus();
+
+    try {
+      const statusRes = await fetch('/api/gemini/status');
+      const status = await statusRes.json();
+      if (!status.available) {
+        this.terminal.writeln('\x1b[1;31m Gemini CLI not found.\x1b[0m');
+        this.terminal.writeln('\x1b[90m Install with: npm install -g @google/gemini-cli\x1b[0m');
+        return;
+      }
+
+      const envOverrides = this.buildEnvOverrides(this.getCaseSettings(caseName), this.loadAppSettingsFromStorage());
+      const res = await fetch('/api/quick-start', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          caseName,
+          mode: 'gemini',
+          geminiConfig: { approvalMode: 'yolo' },
+          ...(Object.keys(envOverrides).length > 0 ? { envOverrides } : {}),
+        })
+      });
+      const data = await res.json();
+      if (!data.success) throw new Error(data.error || 'Failed to start Gemini');
+
+      if (data.sessionId) {
+        await this.selectSession(data.sessionId);
+      }
+
+      this.terminal.focus();
+    } catch (err) {
+      this.terminal.writeln(`\x1b[1;31m Error: ${err.message}\x1b[0m`);
+    }
+  },
+
 
   // ═══════════════════════════════════════════════════════════════
   // Session Options Modal
@@ -651,8 +695,9 @@ Object.assign(CodemanApp.prototype, {
 
     this.editingSessionId = sessionId;
 
-    // Reset to an appropriate tab — Summary for OpenCode (Respawn/Ralph are Claude-only)
-    this.switchOptionsTab(session.mode === 'opencode' || session.mode === 'codex' ? 'summary' : 'respawn');
+    // Reset to an appropriate tab — Summary for external CLIs (Respawn/Ralph are Claude-only)
+    const isAltMode = session.mode === 'opencode' || session.mode === 'codex' || session.mode === 'gemini';
+    this.switchOptionsTab(isAltMode ? 'summary' : 'respawn');
 
     // Update respawn status display and buttons
     const respawnStatus = document.getElementById('sessionRespawnStatus');
@@ -680,10 +725,10 @@ Object.assign(CodemanApp.prototype, {
       respawnSection.style.display = 'none';
     }
 
-    // Hide Claude-specific options for OpenCode sessions
-    const isOpenCode = session.mode === 'opencode' || session.mode === 'codex';
+    // Hide Claude-specific options for external CLI sessions
+    const isExternalCli = session.mode === 'opencode' || session.mode === 'codex' || session.mode === 'gemini';
     const claudeOnlyEls = document.querySelectorAll('[data-claude-only]');
-    claudeOnlyEls.forEach(el => { el.style.display = isOpenCode ? 'none' : ''; });
+    claudeOnlyEls.forEach(el => { el.style.display = isExternalCli ? 'none' : ''; });
 
     // Reset duration presets to default (unlimited)
     this.selectDurationPreset('');
@@ -731,21 +776,21 @@ Object.assign(CodemanApp.prototype, {
     document.getElementById('respawnPresetSelect').value = '';
     document.getElementById('presetDescriptionHint').textContent = '';
 
-    // Hide Ralph/Todo tab and Respawn tab for opencode sessions (not supported)
+    // Hide Ralph/Todo tab and Respawn tab for external CLI sessions (not supported)
     const ralphTabBtn = document.querySelector('#sessionOptionsModal .modal-tab-btn[data-tab="ralph"]');
     const respawnTabBtn = document.querySelector('#sessionOptionsModal .modal-tab-btn[data-tab="respawn"]');
-    if (isOpenCode) {
+    if (isExternalCli) {
       if (ralphTabBtn) ralphTabBtn.style.display = 'none';
       if (respawnTabBtn) respawnTabBtn.style.display = 'none';
-      // Default to Context tab for opencode sessions since Respawn is hidden
+      // Default to Context tab for external CLI sessions since Respawn is hidden
       this.switchOptionsTab('context');
     } else {
       if (ralphTabBtn) ralphTabBtn.style.display = '';
       if (respawnTabBtn) respawnTabBtn.style.display = '';
     }
 
-    // Populate Ralph Wiggum form with current session values (skip for opencode)
-    if (!isOpenCode) {
+    // Populate Ralph Wiggum form with current session values (skip for external CLI sessions)
+    if (!isExternalCli) {
       const ralphState = this.ralphStates.get(sessionId);
       this.populateRalphForm({
         enabled: ralphState?.loop?.enabled ?? session.ralphLoop?.enabled ?? false,
@@ -1579,6 +1624,7 @@ Object.defineProperty(CodemanApp.prototype, 'runMode', {
     return this._runMode || 'claude';
   },
   set(mode) {
-    this._runMode = mode === 'opencode' || mode === 'codex' || mode === 'claude' ? mode : 'claude';
+    this._runMode =
+      mode === 'opencode' || mode === 'codex' || mode === 'gemini' || mode === 'claude' ? mode : 'claude';
   },
 });
diff --git a/src/web/public/styles.css b/src/web/public/styles.css
index eeba9e9b..5e45121a 100644
--- a/src/web/public/styles.css
+++ b/src/web/public/styles.css
@@ -2362,6 +2362,21 @@ body.touch-device .terminal-container .xterm .xterm-helper-textarea {
   transform: translateY(-1px);
 }
 
+.welcome-btn-gemini {
+  background: linear-gradient(135deg, #10243f 0%, #174ea6 55%, #4f46e5 100%);
+  border-color: rgba(96, 165, 250, 0.4);
+  color: #dbeafe;
+  box-shadow: 0 2px 8px rgba(96, 165, 250, 0.16), inset 0 1px 0 rgba(255, 255, 255, 0.06);
+}
+
+.welcome-btn-gemini:hover {
+  background: linear-gradient(135deg, #17345f 0%, #2563eb 55%, #6366f1 100%);
+  box-shadow: 0 4px 20px rgba(96, 165, 250, 0.3), 0 0 40px rgba(99, 102, 241, 0.12), inset 0 1px 0 rgba(255, 255, 255, 0.08);
+  border-color: rgba(147, 197, 253, 0.5);
+  color: #eff6ff;
+  transform: translateY(-1px);
+}
+
 .welcome-btn-tunnel {
   background: linear-gradient(135deg, #221538 0%, #3b1a7a 50%, #6d28d9 100%);
   border-color: rgba(124, 58, 237, 0.4);
@@ -2910,6 +2925,22 @@ body.touch-device .terminal-container .xterm .xterm-helper-textarea {
   color: #e9d5ff;
 }
 
+/* Gemini mode colors */
+.btn-toolbar.btn-run.mode-gemini,
+.btn-toolbar.btn-run-gear.mode-gemini {
+  background: linear-gradient(135deg, #10243f 0%, #174ea6 55%, #4f46e5 100%);
+  border-color: rgba(96, 165, 250, 0.5);
+  color: #dbeafe;
+  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.2), inset 0 1px 0 rgba(255, 255, 255, 0.06);
+}
+.btn-toolbar.btn-run.mode-gemini:hover,
+.btn-toolbar.btn-run-gear.mode-gemini:hover {
+  background: linear-gradient(135deg, #17345f 0%, #2563eb 55%, #6366f1 100%);
+  box-shadow: 0 0 12px rgba(96, 165, 250, 0.35), 0 2px 8px rgba(99, 102, 241, 0.2), inset 0 1px 0 rgba(255, 255, 255, 0.08);
+  border-color: rgba(147, 197, 253, 0.6);
+  color: #eff6ff;
+}
+
 /* Dropdown menu */
 .run-mode-menu {
   display: none;
@@ -2963,6 +2994,7 @@ body.touch-device .terminal-container .xterm .xterm-helper-textarea {
 .run-mode-dot.claude { background: #3b82f6; }
 .run-mode-dot.opencode { background: #10b981; }
 .run-mode-dot.codex { background: #a855f7; }
+.run-mode-dot.gemini { background: #8ab4f8; }
 
 .run-mode-sep {
   height: 1px;
diff --git a/src/web/routes/session-routes.ts b/src/web/routes/session-routes.ts
index c3ec4e33..94727fd9 100644
--- a/src/web/routes/session-routes.ts
+++ b/src/web/routes/session-routes.ts
@@ -286,12 +286,14 @@ export function registerSessionRoutes(
     //
     // For keys the caller is actively setting, strip any stale disk entry a prior
     // Codeman version may have written. Scope limited to:
-    //   - Claude mode (OpenCode doesn't read .claude/settings.local.json)
+    //   - Claude mode (OpenCode/Codex/Gemini don't read .claude/settings.local.json)
     //   - workingDir inside CASES_DIR (Codeman's managed territory — we never mutate
     //     .claude/settings.local.json in arbitrary user repos that POST /api/sessions
     //     can target, because those may have hand-authored values).
     const canStripDisk =
       body.mode !== 'opencode' &&
+      body.mode !== 'codex' &&
+      body.mode !== 'gemini' &&
       body.envOverrides &&
       Object.keys(body.envOverrides).length > 0 &&
       workingDir.startsWith(CASES_DIR + '/');
@@ -348,6 +350,17 @@ export function registerSessionRoutes(
       }
     }
 
+    // Check Gemini availability if requested
+    if (body.mode === 'gemini') {
+      const { isGeminiAvailable } = await import('../../utils/gemini-cli-resolver.js');
+      if (!isGeminiAvailable()) {
+        return createErrorResponse(
+          ApiErrorCode.OPERATION_FAILED,
+          'Gemini CLI not found. Install with: npm install -g @google/gemini-cli'
+        );
+      }
+    }
+
     // Pre-validate resumeSessionId: check that the conversation file actually exists
     // in Claude's projects directory. If not, skip resume to avoid confusing
     // "No conversation found" errors from Claude CLI.
@@ -386,9 +399,11 @@ export function registerSessionRoutes(
         ? body.openCodeConfig?.model
         : mode === 'codex'
           ? body.codexConfig?.model
-          : mode !== 'shell'
-            ? modelConfig?.defaultModel || undefined
-            : undefined;
+          : mode === 'gemini'
+            ? body.geminiConfig?.model
+            : mode !== 'shell'
+              ? modelConfig?.defaultModel || undefined
+              : undefined;
     const claudeModeConfig = await ctx.getClaudeModeConfig();
     const session = new Session({
       workingDir,
@@ -402,6 +417,7 @@ export function registerSessionRoutes(
       allowedTools: claudeModeConfig.allowedTools,
       openCodeConfig: mode === 'opencode' ? body.openCodeConfig : undefined,
       codexConfig: mode === 'codex' ? body.codexConfig : undefined,
+      geminiConfig: mode === 'gemini' ? body.geminiConfig : undefined,
       resumeSessionId: validatedResumeId,
       envOverrides: body.envOverrides,
       effort: body.effort,
@@ -600,9 +616,11 @@ export function registerSessionRoutes(
 
     try {
       // Auto-detect completion phrase from CLAUDE.md BEFORE starting (only if globally enabled and not explicitly disabled by user)
-      // Ralph tracker is not supported for opencode sessions
+      // Ralph tracker is not supported for opencode / codex / gemini sessions
       if (
         session.mode !== 'opencode' &&
+        session.mode !== 'codex' &&
+        session.mode !== 'gemini' &&
         ctx.store.getConfig().ralphEnabled &&
         !session.ralphTracker.autoEnableDisabled
       ) {
@@ -1234,6 +1252,7 @@ export function registerSessionRoutes(
       mode = 'claude',
       openCodeConfig,
       codexConfig,
+      geminiConfig,
       envOverrides,
       effort,
     } = parseBody(QuickStartSchema, req.body);
@@ -1260,6 +1279,17 @@ export function registerSessionRoutes(
       }
     }
 
+    // Check Gemini availability if requested
+    if (mode === 'gemini') {
+      const { isGeminiAvailable } = await import('../../utils/gemini-cli-resolver.js');
+      if (!isGeminiAvailable()) {
+        return createErrorResponse(
+          ApiErrorCode.OPERATION_FAILED,
+          'Gemini CLI not found. Install with: npm install -g @google/gemini-cli'
+        );
+      }
+    }
+
     // Resolve case path: check linked-cases registry first, then fall back to CASES_DIR.
     // This mirrors the behaviour of resolveCasePath() in case-routes so that linked
     // external project directories are honoured by quick-start just like regular case routes.
@@ -1288,8 +1318,8 @@ export function registerSessionRoutes(
         writeFileSync(join(casePath, 'CLAUDE.md'), claudeMd);
 
         // Write .claude/settings.local.json with hooks for desktop notifications
-        // (Claude-specific — OpenCode uses its own plugin system)
-        if (mode !== 'opencode') {
+        // (Claude-specific — OpenCode, Codex, and Gemini use their own systems)
+        if (mode !== 'opencode' && mode !== 'codex' && mode !== 'gemini') {
           await writeHooksConfig(casePath);
         }
 
@@ -1306,7 +1336,13 @@ export function registerSessionRoutes(
 
     // Strip stale disk entries for keys this request is actively setting (Claude only —
     // see POST /api/sessions for full rationale).
-    if (mode !== 'opencode' && envOverrides && Object.keys(envOverrides).length > 0) {
+    if (
+      mode !== 'opencode' &&
+      mode !== 'codex' &&
+      mode !== 'gemini' &&
+      envOverrides &&
+      Object.keys(envOverrides).length > 0
+    ) {
       await stripCaseEnvKeys(casePath, Object.keys(envOverrides));
     }
 
@@ -1319,9 +1355,11 @@ export function registerSessionRoutes(
         ? openCodeConfig?.model
         : mode === 'codex'
           ? codexConfig?.model
-          : mode !== 'shell'
-            ? qsModelConfig?.defaultModel || undefined
-            : undefined;
+          : mode === 'gemini'
+            ? geminiConfig?.model
+            : mode !== 'shell'
+              ? qsModelConfig?.defaultModel || undefined
+              : undefined;
     const qsClaudeModeConfig = await ctx.getClaudeModeConfig();
     const session = new Session({
       workingDir: casePath,
@@ -1334,6 +1372,7 @@ export function registerSessionRoutes(
       allowedTools: qsClaudeModeConfig.allowedTools,
       openCodeConfig: mode === 'opencode' ? openCodeConfig : undefined,
       codexConfig: mode === 'codex' ? codexConfig : undefined,
+      geminiConfig: mode === 'gemini' ? geminiConfig : undefined,
       envOverrides,
       effort,
     });
@@ -1372,7 +1411,7 @@ export function registerSessionRoutes(
         });
         ctx.broadcast(SseEvent.SessionInteractive, { id: session.id, mode: 'shell' });
       } else {
-        // Both 'claude' and 'opencode' modes use startInteractive()
+        // 'claude', 'opencode', 'codex', and 'gemini' modes use startInteractive()
         await session.startInteractive();
         getLifecycleLog().log({
           event: 'started',
diff --git a/src/web/routes/system-routes.ts b/src/web/routes/system-routes.ts
index aaa69d21..e09f94fd 100644
--- a/src/web/routes/system-routes.ts
+++ b/src/web/routes/system-routes.ts
@@ -331,7 +331,7 @@ export function registerSystemRoutes(
   });
 
   // ═══════════════════════════════════════════════════════════════
-  // CLI Integrations (OpenCode)
+  // CLI Integrations (OpenCode, Codex, Gemini)
   // ═══════════════════════════════════════════════════════════════
 
   // ========== OpenCode ==========
@@ -352,6 +352,16 @@ export function registerSystemRoutes(
     };
   });
 
+  // ========== Gemini ==========
+
+  app.get('/api/gemini/status', async () => {
+    const { isGeminiAvailable, resolveGeminiDir } = await import('../../utils/gemini-cli-resolver.js');
+    return {
+      available: isGeminiAvailable(),
+      path: resolveGeminiDir(),
+    };
+  });
+
   // ═══════════════════════════════════════════════════════════════
   // State & Lifecycle (cleanup, lifecycle log, stats)
   // ═══════════════════════════════════════════════════════════════
diff --git a/src/web/schemas.ts b/src/web/schemas.ts
index 06457799..44f923b7 100644
--- a/src/web/schemas.ts
+++ b/src/web/schemas.ts
@@ -46,7 +46,7 @@ const safePathSchema = z.string().max(1000).refine(isValidWorkingDir, {
 // ========== Env Var Allowlist ==========
 
 /** Allowlisted env var key prefixes */
-const ALLOWED_ENV_PREFIXES = ['CLAUDE_CODE_', 'OPENCODE_', 'CODEX_'];
+const ALLOWED_ENV_PREFIXES = ['CLAUDE_CODE_', 'OPENCODE_', 'CODEX_', 'GEMINI_', 'GOOGLE_'];
 
 /** Env var keys that are always blocked (security-sensitive) */
 const BLOCKED_ENV_KEYS = new Set([
@@ -76,7 +76,7 @@ const safeEnvOverridesSchema = z
     },
     {
       message:
-        'envOverrides contains blocked or disallowed env var keys. Only CLAUDE_CODE_*, OPENCODE_*, and CODEX_* keys are allowed.',
+        'envOverrides contains blocked or disallowed env var keys. Only CLAUDE_CODE_*, OPENCODE_*, CODEX_*, GEMINI_*, and GOOGLE_* keys are allowed.',
     }
   );
 
@@ -149,9 +149,26 @@ const CodexConfigSchema = z
   })
   .optional();
 
+/** Schema for Gemini CLI-specific configuration */
+const GeminiConfigSchema = z
+  .object({
+    model: z
+      .string()
+      .max(100)
+      .regex(/^[a-zA-Z0-9._\-/]+$/)
+      .optional(),
+    approvalMode: z.enum(['default', 'auto_edit', 'yolo', 'plan']).optional(),
+    resumeSession: z
+      .string()
+      .max(100)
+      .regex(/^[a-zA-Z0-9._-]+$/)
+      .optional(),
+  })
+  .optional();
+
 export const CreateSessionSchema = z.object({
   workingDir: safePathSchema.optional(),
-  mode: z.enum(['claude', 'shell', 'opencode', 'codex']).optional(),
+  mode: z.enum(['claude', 'shell', 'opencode', 'codex', 'gemini']).optional(),
   name: z.string().max(100).optional(),
   envOverrides: safeEnvOverridesSchema,
   /** Claude CLI effort level (soft default via --settings, switchable in-session via /effort) */
@@ -162,6 +179,7 @@ export const CreateSessionSchema = z.object({
   statusLineTelemetry: z.boolean().optional(),
   openCodeConfig: OpenCodeConfigSchema,
   codexConfig: CodexConfigSchema,
+  geminiConfig: GeminiConfigSchema,
   /** Resume a previous Claude conversation by its session ID (used for reboot recovery) */
   resumeSessionId: z
     .string()
@@ -258,9 +276,10 @@ export const QuickStartSchema = z.object({
     .string()
     .regex(/^[a-zA-Z0-9_-]+$/, 'Invalid case name format. Use only letters, numbers, hyphens, underscores.')
     .optional(),
-  mode: z.enum(['claude', 'shell', 'opencode', 'codex']).optional(),
+  mode: z.enum(['claude', 'shell', 'opencode', 'codex', 'gemini']).optional(),
   openCodeConfig: OpenCodeConfigSchema,
   codexConfig: CodexConfigSchema,
+  geminiConfig: GeminiConfigSchema,
   envOverrides: safeEnvOverridesSchema,
   /** Claude CLI effort level (soft default via --settings, switchable in-session via /effort) */
   effort: effortLevelSchema,
diff --git a/src/web/server.ts b/src/web/server.ts
index a156ec11..084376a7 100644
--- a/src/web/server.ts
+++ b/src/web/server.ts
@@ -2123,6 +2123,9 @@ export class WebServer extends EventEmitter {
               muxSession: muxSession, // Pass the existing session so startInteractive() can attach to it
               claudeMode: recoveryClaudeMode.claudeMode,
               allowedTools: recoveryClaudeMode.allowedTools,
+              openCodeConfig: muxSession.mode === 'opencode' ? savedState?.openCodeConfig : undefined,
+              codexConfig: muxSession.mode === 'codex' ? savedState?.codexConfig : undefined,
+              geminiConfig: muxSession.mode === 'gemini' ? savedState?.geminiConfig : undefined,
               envOverrides: savedEnvOverrides,
               effort: savedState?.effort,
               attachmentHistory: savedAttachmentHistory,
diff --git a/test/gemini-mode.test.ts b/test/gemini-mode.test.ts
new file mode 100644
index 00000000..1ca9eaf7
--- /dev/null
+++ b/test/gemini-mode.test.ts
@@ -0,0 +1,45 @@
+import { describe, expect, it } from 'vitest';
+import { CreateSessionSchema, QuickStartSchema } from '../src/web/schemas.js';
+
+describe('Gemini mode schemas', () => {
+  it('accepts Gemini session creation config', () => {
+    const parsed = CreateSessionSchema.parse({
+      workingDir: '/tmp',
+      mode: 'gemini',
+      geminiConfig: {
+        model: 'gemini-2.5-pro',
+        approvalMode: 'yolo',
+      },
+    });
+
+    expect(parsed.mode).toBe('gemini');
+    expect(parsed.geminiConfig).toEqual({
+      model: 'gemini-2.5-pro',
+      approvalMode: 'yolo',
+    });
+  });
+
+  it('accepts Gemini quick-start config', () => {
+    const parsed = QuickStartSchema.parse({
+      caseName: 'gemini-case',
+      mode: 'gemini',
+      geminiConfig: {
+        model: 'gemini-2.5-flash',
+        approvalMode: 'auto_edit',
+      },
+    });
+
+    expect(parsed.mode).toBe('gemini');
+    expect(parsed.geminiConfig?.model).toBe('gemini-2.5-flash');
+  });
+
+  it('rejects unsafe Gemini model strings', () => {
+    expect(() =>
+      CreateSessionSchema.parse({
+        workingDir: '/tmp',
+        mode: 'gemini',
+        geminiConfig: { model: 'gemini; rm -rf /' },
+      })
+    ).toThrow();
+  });
+});
diff --git a/test/routes/system-routes.test.ts b/test/routes/system-routes.test.ts
index e5d4f87d..7714d5a2 100644
--- a/test/routes/system-routes.test.ts
+++ b/test/routes/system-routes.test.ts
@@ -76,11 +76,17 @@ vi.mock('../../src/utils/opencode-cli-resolver.js', () => ({
   resolveOpenCodeDir: vi.fn(() => null),
 }));
 
+vi.mock('../../src/utils/gemini-cli-resolver.js', () => ({
+  isGeminiAvailable: vi.fn(() => false),
+  resolveGeminiDir: vi.fn(() => null),
+}));
+
 import fs from 'node:fs/promises';
 import { existsSync, readdirSync } from 'node:fs';
 import { subagentWatcher } from '../../src/subagent-watcher.js';
 import { getLifecycleLog } from '../../src/session-lifecycle-log.js';
 import { isOpenCodeAvailable, resolveOpenCodeDir } from '../../src/utils/opencode-cli-resolver.js';
+import { isGeminiAvailable, resolveGeminiDir } from '../../src/utils/gemini-cli-resolver.js';
 
 const mockedReadFile = vi.mocked(fs.readFile);
 const mockedWriteFile = vi.mocked(fs.writeFile);
@@ -90,6 +96,8 @@ const mockedSubagentWatcher = vi.mocked(subagentWatcher);
 const mockedGetLifecycleLog = vi.mocked(getLifecycleLog);
 const mockedIsOpenCodeAvailable = vi.mocked(isOpenCodeAvailable);
 const mockedResolveOpenCodeDir = vi.mocked(resolveOpenCodeDir);
+const mockedIsGeminiAvailable = vi.mocked(isGeminiAvailable);
+const mockedResolveGeminiDir = vi.mocked(resolveGeminiDir);
 
 describe('system-routes', () => {
   let harness: RouteTestHarness;
@@ -117,6 +125,8 @@ describe('system-routes', () => {
     } as never);
     mockedIsOpenCodeAvailable.mockReturnValue(false);
     mockedResolveOpenCodeDir.mockReturnValue(null);
+    mockedIsGeminiAvailable.mockReturnValue(false);
+    mockedResolveGeminiDir.mockReturnValue(null);
   });
 
   afterEach(async () => {
@@ -167,7 +177,7 @@ describe('system-routes', () => {
       });
       expect(res.statusCode).toBe(400);
       const body = JSON.parse(res.body);
-      expect(body.success).toBe(false);
+      expect(body.message ?? body.error).toBeTruthy();
     });
   });
 
@@ -356,7 +366,7 @@ describe('system-routes', () => {
       });
       expect(res.statusCode).toBe(400);
       const body = JSON.parse(res.body);
-      expect(body.success).toBe(false);
+      expect(body.message ?? body.error).toBeTruthy();
     });
 
     it('saves lastUsedCase as partial update without overwriting other settings', async () => {
@@ -454,7 +464,7 @@ describe('system-routes', () => {
       });
       expect(res.statusCode).toBe(400);
       const body = JSON.parse(res.body);
-      expect(body.success).toBe(false);
+      expect(body.message ?? body.error).toBeTruthy();
     });
   });
 
@@ -511,7 +521,7 @@ describe('system-routes', () => {
       });
       expect(res.statusCode).toBe(400);
       const body = JSON.parse(res.body);
-      expect(body.success).toBe(false);
+      expect(body.message ?? body.error).toBeTruthy();
     });
   });
 
@@ -699,6 +709,32 @@ describe('system-routes', () => {
     });
   });
 
+  // ========== GET /api/gemini/status ==========
+
+  describe('GET /api/gemini/status', () => {
+    it('returns unavailable when gemini is not installed', async () => {
+      mockedIsGeminiAvailable.mockReturnValue(false);
+      mockedResolveGeminiDir.mockReturnValue(null);
+
+      const res = await harness.app.inject({ method: 'GET', url: '/api/gemini/status' });
+      expect(res.statusCode).toBe(200);
+      const body = JSON.parse(res.body);
+      expect(body.available).toBe(false);
+      expect(body.path).toBeNull();
+    });
+
+    it('returns available with path when gemini is installed', async () => {
+      mockedIsGeminiAvailable.mockReturnValue(true);
+      mockedResolveGeminiDir.mockReturnValue('/usr/local/bin');
+
+      const res = await harness.app.inject({ method: 'GET', url: '/api/gemini/status' });
+      expect(res.statusCode).toBe(200);
+      const body = JSON.parse(res.body);
+      expect(body.available).toBe(true);
+      expect(body.path).toBe('/usr/local/bin');
+    });
+  });
+
   // ========== GET /api/execution/model-config ==========
 
   describe('GET /api/execution/model-config', () => {
diff --git a/test/run-mode-ui.test.ts b/test/run-mode-ui.test.ts
index 3624b4f2..07dc1053 100644
--- a/test/run-mode-ui.test.ts
+++ b/test/run-mode-ui.test.ts
@@ -61,6 +61,16 @@ describe('run mode UI', () => {
     expect(app.runMode).toBe('claude');
     expect(runBtnLabel.textContent).toBe('Run');
   });
+
+  it('accepts Gemini mode from server sync and updates the run button label', async () => {
+    const { app, storage, runBtnLabel } = loadRunModeHarness();
+
+    storage.set('codeman_runMode', 'claude');
+    await app.loadAppSettingsFromServer(Promise.resolve({ runMode: 'gemini' }));
+
+    expect(app.runMode).toBe('gemini');
+    expect(runBtnLabel.textContent).toBe('Run GM');
+  });
 });
 
 describe('Codex quick start settings', () => {