Add configurable hook context spill limits (#34393)

## What changed

- Add `additionalContextLimit` to command hook configuration for events that can emit `additionalContext`.
- Apply the limit independently to each hook's context before it is sent to the model. Unset values retain the 2,500-token default, while `0` disables spilling for that hook.
- Expose configured limits through app-server hook and requirements responses, and show them in the TUI hooks browser.

## Testing

- Cover JSON and TOML parsing, discovery and hashing, per-hook spilling behavior, app-server responses, and TUI rendering.

GitOrigin-RevId: 55ddc2dbbdf9067dceee3e1968c03617bbf6bcea

codex-rs/app-server-protocol/src/protocol/v2/config.rs

@@ -484,6 +484,13 @@ pub enum ConfiguredHookHandler {
         #[serde(rename = "statusMessage")]
         #[ts(rename = "statusMessage")]
         status_message: Option<String>,
+        /// Approximate token threshold for spilling this hook's `additionalContext` to disk.
+        /// `null` uses 2,500 tokens; `0` disables spilling for this hook. The threshold is
+        /// evaluated against the original context; a spilled preview also includes recovery
+        /// metadata.
+        #[serde(rename = "additionalContextLimit")]
+        #[ts(rename = "additionalContextLimit")]
+        additional_context_limit: Option<usize>,
     },
     #[serde(rename = "prompt")]
     #[ts(rename = "prompt")]

codex-rs/app-server-protocol/src/protocol/v2/plugin.rs

@@ -519,6 +519,9 @@ pub struct HookMetadata {
     pub command: Option<String>,
     pub timeout_sec: u64,
     pub status_message: Option<String>,
+    /// Configured `additionalContext` spill threshold.
+    /// `null` uses 2,500 tokens; `0` disables spilling.
+    pub additional_context_limit: Option<usize>,
     pub source_path: AbsolutePathBuf,
     pub source: HookSource,
     pub plugin_id: Option<String>,