feat(acp): Add agent switcher to ACP CLI (#84)

Implements agent/model switching for ACP mode:
- Add /agent slash command to open agent picker popup
- Add agent_picker component in nori/ with SelectionViewParams
- Track pending agent selection - switch happens on next prompt
submission
- Modify /model to show disabled options in ACP mode with redirect to
/agent
- Add list_available_agents() and AcpAgentInfo to ACP registry
- Add AppEvent variants for SetPendingAgent, ClearPendingAgent,
SubmitWithAgentSwitch
- Add ACP file tracing initialization to TUI
- Add E2E tests for agent switching behavior

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Nori <contact@tilework.tech>

Author: 3 people

codex-rs/acp/src/lib.rs

@@ -14,8 +14,10 @@ pub use backend::AcpBackendConfig;
 pub use connection::AcpConnection;
 pub use connection::ApprovalRequest;
 pub use registry::AcpAgentConfig;
+pub use registry::AcpAgentInfo;
 pub use registry::AcpProviderInfo;
 pub use registry::get_agent_config;
+pub use registry::list_available_agents;
 pub use tracing_setup::init_file_tracing;
 pub use translator::TranslatedEvent;
 pub use translator::translate_session_update;

codex-rs/acp/src/registry.rs

@@ -6,6 +6,49 @@
 use anyhow::Result;
 use std::time::Duration;
 
+/// Information about an available ACP agent for display in the picker
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct AcpAgentInfo {
+    /// Model name used to select this agent (e.g., "mock-model", "gemini-2.5-flash")
+    pub model_name: String,
+    /// Display name shown in the picker
+    pub display_name: String,
+    /// Description of the agent
+    pub description: String,
+    /// Provider slug for this agent
+    pub provider_slug: String,
+}
+
+/// Get list of all available ACP agents for the agent picker
+pub fn list_available_agents() -> Vec<AcpAgentInfo> {
+    vec![
+        AcpAgentInfo {
+            model_name: "mock-model".to_string(),
+            display_name: "Mock ACP".to_string(),
+            description: "Mock agent for testing".to_string(),
+            provider_slug: "mock-acp".to_string(),
+        },
+        AcpAgentInfo {
+            model_name: "mock-model-alt".to_string(),
+            display_name: "Mock ACP Alt".to_string(),
+            description: "Alternate mock agent for testing".to_string(),
+            provider_slug: "mock-acp-alt".to_string(),
+        },
+        AcpAgentInfo {
+            model_name: "gemini-2.5-flash".to_string(),
+            display_name: "Gemini 2.5 Flash".to_string(),
+            description: "Google Gemini via ACP".to_string(),
+            provider_slug: "gemini-acp".to_string(),
+        },
+        AcpAgentInfo {
+            model_name: "claude-4.5".to_string(),
+            display_name: "Claude 4.5".to_string(),
+            description: "Anthropic Claude via ACP".to_string(),
+            provider_slug: "claude-acp".to_string(),
+        },
+    ]
+}
+
 /// Default idle timeout for ACP streaming (5 minutes)
 const DEFAULT_STREAM_IDLE_TIMEOUT: Duration = Duration::from_secs(300);
 

codex-rs/tui-pty-e2e/docs.md

@@ -145,7 +145,7 @@ This delay allows the PTY subprocess time to process input and update the displa
 | `@/codex-rs/tui-pty-e2e/tests/input_handling.rs` | Text editing, backspace, Ctrl-C clearing, arrow key navigation with snapshot testing |
 | `@/codex-rs/tui-pty-e2e/tests/streaming.rs` | Prompt submission with timing delays, agent response streaming |
 | `@/codex-rs/tui-pty-e2e/tests/acp_mode.rs` | ACP mode startup, response flow, and approval bridging - validates TUI works with ACP wire API and mock agent; includes test for permission request display |
-| `@/codex-rs/tui-pty-e2e/tests/agent_switching.rs` | ACP agent subprocess lifecycle - verifies subprocess spawning, cleanup on session switch, and different agents use different processes (Linux only) |
+| `@/codex-rs/tui-pty-e2e/tests/agent_switching.rs` | ACP agent subprocess lifecycle and event isolation - verifies subprocess spawning, cleanup on session switch, different agents use different processes, and event filtering prevents cross-agent contamination (Linux only) |
 | `@/codex-rs/tui-pty-e2e/tests/live_acp.rs` | Live authenticated ACP tests for Gemini and Claude with real API connections (opt-in, marked `#[ignore]`) |
 
 **Snapshot Files:**
@@ -237,7 +237,9 @@ See `@/codex-rs/mock-acp-agent/docs.md` for full list of env vars.
 
 **Agent Subprocess Lifecycle Testing (`agent_switching.rs`):**
 
-Linux-only tests that verify ACP subprocess lifecycle management by parsing the `.codex-acp.log` file for PID entries:
+Linux-only tests that verify ACP subprocess lifecycle management and event isolation:
+
+*Subprocess Management Tests:*
 - `acp_log_path()` method on `TuiSession` returns the path to the ACP tracing log file
 - Tests extract PIDs from log lines matching `"ACP agent spawned (pid: Some(...))"`
 - Uses `/proc/{pid}` filesystem to verify process existence and zombie state
@@ -248,6 +250,11 @@ Linux-only tests that verify ACP subprocess lifecycle management by parsing the
   - Cleanup happens when session switches, not when individual prompt turns end
   - Different models (`mock-model` vs `mock-model-alt`) spawn different subprocesses
 
+*Event Isolation Tests:*
+- `extract_agent_messages_from_log()` helper parses `Mock agent:` log entries from ACP log file
+- `test_agent_switch_message_flow_mock_to_mock_alt` verifies that after switching agents, the NEW agent receives and responds to prompts (catches race conditions where OLD agent events could leak)
+- `test_agent_switch_logs_correct_sequence` verifies the expected log sequence during agent switch: agent receives prompt, logs receipt, sends response
+
 **Binary Discovery:**
 
 `codex_binary_path()` locates the compiled binary: