[1/3] Parse exec commands and format them more nicely in the UI (#2095)

# Note for reviewers
The bulk of this PR is in in the new file, `parse_command.rs`. This file
is designed to be written TDD and implemented with Codex. Do not worry
about reviewing the code, just review the unit tests (if you want). If
any cases are missing, we'll add more tests and have Codex fix them.

I think the best approach will be to land and iterate. I have some
follow-ups I want to do after this lands. The next PR after this will
let us merge (and dedupe) multiple sequential cells of the same such as
multiple read commands. The deduping will also be important because the
model often reads the same file multiple times in a row in chunks

===

This PR formats common commands like reading, formatting, testing, etc
more nicely:

It tries to extract things like file names, tests and falls back to the
cmd if it doesn't. It also only shows stdout/err if the command failed.

<img width="770" height="238" alt="CleanShot 2025-08-09 at 16 05 15"
src="https://github.com/user-attachments/assets/0ead179a-8910-486b-aa3d-7d26264d751e"
/>
<img width="348" height="158" alt="CleanShot 2025-08-09 at 16 05 32"
src="https://github.com/user-attachments/assets/4302681b-5e87-4ff3-85b4-0252c6c485a9"
/>
<img width="834" height="324" alt="CleanShot 2025-08-09 at 16 05 56 2"
src="https://github.com/user-attachments/assets/09fb3517-7bd6-40f6-a126-4172106b700f"
/>

Part 2: https://github.com/openai/codex/pull/2097
Part 3: https://github.com/openai/codex/pull/2110

codex-rs/core/src/codex.rs

@@ -65,6 +65,7 @@ use crate::models::ResponseItem;
 use crate::models::ShellToolCallParams;
 use crate::openai_tools::ToolsConfig;
 use crate::openai_tools::get_openai_tools;
+use crate::parse_command::parse_command;
 use crate::plan_tool::handle_update_plan;
 use crate::project_doc::get_user_instructions;
 use crate::protocol::AgentMessageDeltaEvent;
@@ -402,6 +403,7 @@ impl Session {
                 call_id,
                 command: command_for_display.clone(),
                 cwd,
+                parsed_cmd: parse_command(&command_for_display),
             }),
         };
         let event = Event {

codex-rs/core/src/lib.rs

@@ -28,6 +28,7 @@ mod mcp_connection_manager;
 mod mcp_tool_call;
 mod message_history;
 mod model_provider_info;
+pub mod parse_command;
 pub use model_provider_info::BUILT_IN_OSS_MODEL_PROVIDER_ID;
 pub use model_provider_info::ModelProviderInfo;
 pub use model_provider_info::WireApi;

codex-rs/core/src/protocol.rs

@@ -21,6 +21,7 @@ use crate::config_types::ReasoningEffort as ReasoningEffortConfig;
 use crate::config_types::ReasoningSummary as ReasoningSummaryConfig;
 use crate::message_history::HistoryEntry;
 use crate::model_provider_info::ModelProviderInfo;
+use crate::parse_command::ParsedCommand;
 use crate::plan_tool::UpdatePlanArgs;
 
 /// Submission Queue Entry - requests from user
@@ -579,6 +580,7 @@ pub struct ExecCommandBeginEvent {
     pub command: Vec<String>,
     /// The command's working directory if not the default cwd for the agent.
     pub cwd: PathBuf,
+    pub parsed_cmd: Vec<ParsedCommand>,
 }
 
 #[derive(Debug, Clone, Deserialize, Serialize)]