Unify Guardian context section collection (#42076)

## What changed

- Add typed context sections for root-conversation evidence, trusted user answers, and conversation transcripts to `codex-guardian-context`.
- Use the shared section registry when building core Guardian prompts and asynchronous Guardian V2 scoring context.
- Preserve source-role labeling while delivering authorization evidence as user-role context, and fail closed when context collection fails.

## Testing

- Cover shared section ordering and role preservation for synchronous and asynchronous targets.
- Verify trusted user answers appear exactly once as user-role input in Guardian V2 approval flows.

GitOrigin-RevId: 1d5d793ffbf166077411a66e85e039596907fb7e

codex-rs/guardian-context/src/lib.rs

@@ -14,8 +14,12 @@ use std::sync::LazyLock;
 
 use codex_protocol::models::ResponseItem;
 
+use authorization::RootConversationSection;
+use authorization::TrustedUserAnswersSection;
 use transcript::ConversationTranscriptSection;
 
+pub use authorization::GuardianRootMessage;
+
 pub use entry::ConversationTranscriptEntry;
 pub use entry::ConversationTranscriptEntryKind;
 pub use history::TranscriptHistory;
@@ -30,6 +34,7 @@ pub use transcript::TranscriptRetentionConfig;
 pub use transcript::collect_transcript;
 pub use truncation::truncate_text;
 
+mod authorization;
 mod entry;
 mod history;
 mod retention;
@@ -76,6 +81,10 @@ pub struct SectionInput<'a> {
     pub history: &'a dyn SectionHistory,
     /// Evidence sources and per-entry limits for this collection.
     pub transcript: &'a ConversationTranscriptConfig,
+    /// Bounded root evidence resolved by the host; empty when not applicable.
+    pub root_conversation: &'a [GuardianRootMessage],
+    /// Bounded, role-labeled answers verified and matched to history by the host.
+    pub trusted_user_answers: &'a [String],
 }
 
 /// Supplies repeatable, zero-copy access to a host-owned conversation snapshot.
@@ -153,6 +162,8 @@ pub struct SectionRegistry {
 pub fn default_registry() -> &'static SectionRegistry {
     static REGISTRY: LazyLock<SectionRegistry> = LazyLock::new(|| {
         let mut registry = SectionRegistry::default();
+        registry.register(RootConversationSection);
+        registry.register(TrustedUserAnswersSection);
         registry.register(ConversationTranscriptSection);
         registry
     });
@@ -178,11 +189,23 @@ impl SectionRegistry {
     }
 }
 
-/// Ordered transcript evidence produced by one section contributor.
+/// Ordered evidence with a stable section identity and source-specific content.
+///
+/// Variants preserve provenance: transcript entries carry their original roles,
+/// root messages remain line-role-labeled, and answers are host-verified fragments.
+/// All currently supported sections are delivered as user-role evidence. Source
+/// attribution never promotes their contents to developer instructions.
 #[derive(Clone, Debug, PartialEq)]
-pub struct ContextSection {
-    /// Structured evidence before consumer-specific selection and rendering.
-    pub items: Vec<ConversationTranscriptEntry>,
+pub enum ContextSection {
+    ConversationTranscript {
+        items: Vec<ConversationTranscriptEntry>,
+    },
+    RootConversation {
+        items: Vec<String>,
+    },
+    TrustedUserAnswers {
+        items: Vec<String>,
+    },
 }
 
 #[cfg(test)]