Add history and notes tools for token-budget sessions (#39827)

## Why

Token-budget sessions need a way to recover prior conversation context and preserve working state across context-window transitions.

## What changed

- Add direct-model `history` tools for listing windows and items, reading items, and searching conversation contents.
- Add direct-model `notes` tools for listing, reading, searching, appending, and writing persistent notes.
- Route tool calls through the configured Codex backend with trusted session and agent context, bounded request arguments, and truncation-aware output handling.
- Expose the extension when `features.token_budget.use_history_notes_history` is enabled with an OpenAI provider and Codex backend authentication.

## Testing

- Cover tool registration, configuration changes, provider and authentication requirements, backend request context, encrypted output preservation, and request and response limits.

GitOrigin-RevId: 43b259f01014ba3f30803dd7cd5634942407a9bb

codex-rs/core/src/config/config_tests.rs

@@ -654,6 +654,7 @@ async fn load_config_resolves_token_budget_config() -> std::io::Result<()> {
             r#"
 [features.token_budget]
 enabled = true
+use_history_notes_history = true
 reminder_threshold_tokens = 16000
 reminder_message_template = "Custom reminder: {n_remaining} tokens."
 guidance_message = "Preserve important state before compaction."
@@ -661,6 +662,7 @@ auto_compact_fallback_prompt = "  Write notes immediately.  "
 auto_compact_fallback_buffer_tokens = 8000
 "#,
             TokenBudgetConfig {
+                use_history_notes_history: true,
                 reminder_threshold_tokens: Some(16_000),
                 reminder_message_template: "Custom reminder: {n_remaining} tokens.".to_string(),
                 guidance_message: Some("Preserve important state before compaction.".to_string()),

codex-rs/core/src/config/mod.rs

@@ -1087,6 +1087,7 @@ const AUTO_COMPACT_FALLBACK_PROMPT_MAX_BYTES: usize = 2000;
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize)]
 pub struct TokenBudgetConfig {
+    pub use_history_notes_history: bool,
     pub reminder_threshold_tokens: Option<i64>,
     pub reminder_message_template: String,
     pub guidance_message: Option<String>,
@@ -1179,6 +1180,7 @@ impl TokenBudgetConfig {
 impl Default for TokenBudgetConfig {
     fn default() -> Self {
         Self {
+            use_history_notes_history: false,
             reminder_threshold_tokens: None,
             reminder_message_template: DEFAULT_TOKEN_BUDGET_REMINDER_MESSAGE_TEMPLATE.to_string(),
             guidance_message: None,
@@ -2718,6 +2720,9 @@ fn resolve_token_budget_config(
     }
 
     let token_budget_config = token_budget_toml_config(config_toml.features.as_ref());
+    let use_history_notes_history = token_budget_config
+        .and_then(|config| config.use_history_notes_history)
+        .unwrap_or_default();
     let reminder_threshold_tokens =
         token_budget_config.and_then(|config| config.reminder_threshold_tokens);
     let reminder_message_template = token_budget_config
@@ -2735,6 +2740,7 @@ fn resolve_token_budget_config(
         token_budget_config.and_then(|config| config.auto_compact_fallback_buffer_tokens);
 
     let token_budget = TokenBudgetConfig {
+        use_history_notes_history,
         reminder_threshold_tokens,
         reminder_message_template,
         guidance_message,