enable-resume (#3537)

Adding the ability to resume conversations.
we have one verb `resume`. 

Behavior:

`tui`:
`codex resume`: opens session picker
`codex resume --last`: continue last message
`codex resume <session id>`: continue conversation with `session id`

`exec`:
`codex resume --last`: continue last conversation
`codex resume <session id>`: continue conversation with `session id`

Implementation:
- I added a function to find the path in `~/.codex/sessions/` with a
`UUID`. This is helpful in resuming with session id.
- Added the above mentioned flags
- Added lots of testing

codex-rs/core/src/config.rs

@@ -161,9 +161,6 @@ pub struct Config {
     /// Base URL for requests to ChatGPT (as opposed to the OpenAI API).
     pub chatgpt_base_url: String,
 
-    /// Experimental rollout resume path (absolute path to .jsonl; undocumented).
-    pub experimental_resume: Option<PathBuf>,
-
     /// Include an experimental plan tool that the model can use to update its current plan and status of each step.
     pub include_plan_tool: bool,
 
@@ -603,9 +600,6 @@ pub struct ConfigToml {
     /// Base URL for requests to ChatGPT (as opposed to the OpenAI API).
     pub chatgpt_base_url: Option<String>,
 
-    /// Experimental rollout resume path (absolute path to .jsonl; undocumented).
-    pub experimental_resume: Option<PathBuf>,
-
     /// Experimental path to a file whose contents replace the built-in BASE_INSTRUCTIONS.
     pub experimental_instructions_file: Option<PathBuf>,
 
@@ -892,8 +886,6 @@ impl Config {
                 .and_then(|info| info.auto_compact_token_limit)
         });
 
-        let experimental_resume = cfg.experimental_resume;
-
         // Load base instructions override from a file if specified. If the
         // path is relative, resolve it against the effective cwd so the
         // behaviour matches other path-like config values.
@@ -954,8 +946,6 @@ impl Config {
                 .chatgpt_base_url
                 .or(cfg.chatgpt_base_url)
                 .unwrap_or("https://chatgpt.com/backend-api/".to_string()),
-
-            experimental_resume,
             include_plan_tool: include_plan_tool.unwrap_or(false),
             include_apply_patch_tool: include_apply_patch_tool.unwrap_or(false),
             tools_web_search_request,
@@ -1481,7 +1471,6 @@ model_verbosity = "high"
                 model_reasoning_summary: ReasoningSummary::Detailed,
                 model_verbosity: None,
                 chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
-                experimental_resume: None,
                 base_instructions: None,
                 include_plan_tool: false,
                 include_apply_patch_tool: false,
@@ -1539,7 +1528,6 @@ model_verbosity = "high"
             model_reasoning_summary: ReasoningSummary::default(),
             model_verbosity: None,
             chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
-            experimental_resume: None,
             base_instructions: None,
             include_plan_tool: false,
             include_apply_patch_tool: false,
@@ -1612,7 +1600,6 @@ model_verbosity = "high"
             model_reasoning_summary: ReasoningSummary::default(),
             model_verbosity: None,
             chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
-            experimental_resume: None,
             base_instructions: None,
             include_plan_tool: false,
             include_apply_patch_tool: false,
@@ -1671,7 +1658,6 @@ model_verbosity = "high"
             model_reasoning_summary: ReasoningSummary::Detailed,
             model_verbosity: Some(Verbosity::High),
             chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
-            experimental_resume: None,
             base_instructions: None,
             include_plan_tool: false,
             include_apply_patch_tool: false,