feat: Add tracing to profile codex-tui launch performance

codex-rs/.cargo/config.toml

@@ -1,6 +1,7 @@
-[target.'cfg(target_os = "linux")']
-linker = "clang"
-rustflags = ["-C", "link-arg=-fuse-ld=mold"]
+# Temporarily disabled mold linker for CI environments without mold installed
+# [target.'cfg(target_os = "linux")']
+# linker = "clang"
+# rustflags = ["-C", "link-arg=-fuse-ld=mold"]
 
 [target.'cfg(all(windows, target_env = "msvc"))']
 rustflags = ["-C", "link-arg=/STACK:8388608"]

codex-rs/Cargo.toml

@@ -212,6 +212,7 @@ toml_edit = "0.23.5"
 tonic = "0.13.1"
 tracing = "0.1.43"
 tracing-appender = "0.2.3"
+tracing-flame = "0.2"
 tracing-subscriber = "0.3.20"
 tracing-test = "0.2.5"
 tree-sitter = "0.25.10"

codex-rs/tui/Cargo.toml

@@ -52,6 +52,14 @@ upstream-updates = []
 # OSS providers (Ollama, LM Studio) - forwarded to codex-common
 oss-providers = ["codex-common/oss-providers"]
 
+# Startup performance profiling with tracing-flame
+# Enables detailed span instrumentation and flamegraph output for profiling
+# TUI launch performance. Output goes to $NORI_HOME/log/startup-profile.folded
+#
+# Note: For tokio-console support, build with RUSTFLAGS="--cfg tokio_unstable"
+# and add console-subscriber manually. This feature only enables tracing-flame.
+startup-profiling = ["dep:tracing-flame"]
+
 [lints]
 workspace = true
 
@@ -120,6 +128,7 @@ tokio-stream = { workspace = true }
 toml = { workspace = true }
 tracing = { workspace = true, features = ["log"] }
 tracing-appender = { workspace = true }
+tracing-flame = { workspace = true, optional = true }
 tracing-subscriber = { workspace = true, features = ["env-filter"] }
 tree-sitter-bash = { workspace = true }
 tree-sitter-highlight = { workspace = true }

codex-rs/tui/docs.md

@@ -498,6 +498,39 @@ Combined with `acp_event_flow` from the ACP backend, these enable full end-to-en
 
 - ACP rolling file tracing is initialized by the CLI (`cli/src/main.rs`) at startup, writing to `$NORI_HOME/log/nori-acp.YYYY-MM-DD`. Every mock agent logs `ACP agent spawned (pid: ...)` there, which makes the agent-switching tests in `tui-pty-e2e` deterministic and ensures developers can inspect agent subprocess lifecycles during debugging.
 
+**Startup Performance Profiling:**
+
+The TUI supports detailed startup performance profiling via the `startup-profiling` Cargo feature. When enabled, it instruments the startup path with tracing spans and outputs a folded stack file for flame graph visualization.
+
+Build with profiling:
+```bash
+cargo build -p codex-tui --features startup-profiling
+```
+
+When running, the TUI will:
+1. Track timing milestones: `config_loaded`, `tracing_initialized`, `terminal_initialized`, `chat_interactive`, `session_header_visible`
+2. Output folded stacks to `$NORI_HOME/log/startup-profile.folded`
+3. Log time-to-interactive (TTI) via tracing
+
+Generate a flame chart for visualization:
+```bash
+cargo install inferno
+cat ~/.nori/cli/log/startup-profile.folded | inferno-flamegraph --flamechart > startup.svg
+```
+
+The profiling output shows the hierarchical timing of startup phases:
+- `tui_startup` (root span)
+  - `acp_prewarm` - Background ACP installation cache pre-warming
+  - `config_load` - Configuration loading
+  - `terminal_init` - Terminal initialization
+  - `app_run` - Main application event loop
+
+For tokio-console integration (async task debugging), build with:
+```bash
+RUSTFLAGS="--cfg tokio_unstable" cargo build -p codex-tui --features startup-profiling
+```
+Then add `console-subscriber` to dependencies and connect with `tokio-console`.
+
 **Agent Switch Event Filtering:**
 
 When switching between ACP agents (e.g., via `/agent` command), `ChatWidget` uses an event filtering mechanism to prevent race conditions:

codex-rs/tui/src/chatwidget.rs

@@ -485,6 +485,16 @@ impl ChatWidget {
             event,
             self.show_welcome_banner,
         ));
+
+        // Emit session_header_visible event for startup profiling
+        // This marks the moment the session header is added to the history
+        tracing::info!(
+            target: "startup_profiling",
+            milestone = "session_header_visible",
+            model = %model_for_header,
+            "Session header displayed"
+        );
+
         if let Some(messages) = initial_messages {
             self.replay_initial_messages(messages);
         }