Support typed content in contextual prompt fragments (#54776)

## Why

Contextual fragments and extension-owned world-state sections currently return strings, limiting them to text content.

## What changed

- Return `ContentItem` from fragment bodies and rendering, preserving classification and attribution. Apply text markers only to `InputText`; pass other content through unchanged.
- Allow extension prompt and world-state contributions to carry typed content, and preserve media in context-window hints.
- Hash non-text world-state fragments by their serialized content and role while retaining the existing text hashing behavior.
- Add shared content-to-tool-output conversion that preserves image references, image detail, and audio.

## Testing

Add coverage for typed world-state hashing and preservation of image content and attribution. Expand code-mode output tests to cover input text, output text, file-backed and inline images, and audio.

GitOrigin-RevId: 2ed00d466a3f169b151202f3eef71e667ea64be1

codex-rs/ext/git-attribution/src/world_state.rs

@@ -1,6 +1,7 @@
 use codex_extension_api::PreviousWorldStateSection;
 use codex_extension_api::RenderedWorldStateFragment;
 use codex_extension_api::WorldStateSectionContribution;
+use codex_extension_api::input_text;
 use serde_json::Value;
 
 const WORLD_STATE_ID: &str = "git_attribution";
@@ -36,13 +37,13 @@ pub(super) fn git_attribution_world_state_section(enabled: bool) -> WorldStateSe
             | (true, PreviousWorldStateSection::Known(_)) => Some(RenderedWorldStateFragment::new(
                 "developer",
                 (START_MARKER, END_MARKER),
-                ENABLED_INSTRUCTIONS,
+                input_text(ENABLED_INSTRUCTIONS),
             )),
             (false, PreviousWorldStateSection::Known(Value::Bool(true)))
             | (false, PreviousWorldStateSection::Unknown) => Some(RenderedWorldStateFragment::new(
                 "developer",
                 (START_MARKER, END_MARKER),
-                DISABLED_INSTRUCTIONS,
+                input_text(DISABLED_INSTRUCTIONS),
             )),
             (false, PreviousWorldStateSection::Absent)
             | (false, PreviousWorldStateSection::Known(_)) => None,