[codex] Add comp_hash to model metadata (#27532)

## Summary
- add optional `comp_hash` metadata to `ModelInfo`
- update `ModelInfo` fixtures for the shared schema change
- keep older model responses compatible by defaulting the field to
`None`

## Why
The models endpoint needs an opaque identifier for compaction-compatible
model configurations. This PR only exposes that value in model metadata;
it does not add it to turn context or change runtime behavior.

Follow-up #27520 carries the value through turn context and rollouts,
then uses it to trigger compaction.

## Stack
- based directly on `main`
- replaces #27519, which was accidentally merged into the wrong base
branch
- functionality follow-up: #27520

## Testing
- `just test -p codex-protocol
model_info_defaults_availability_nux_to_none_when_omitted`
- `just fix -p codex-core -p codex-protocol -p codex-analytics -p
codex-models-manager`

codex-rs/core/tests/suite/auto_review.rs

@@ -256,6 +256,7 @@ fn remote_model_with_auto_review_override(slug: &str, review_model: &str) -> Mod
         context_window: Some(272_000),
         max_context_window: None,
         auto_compact_token_limit: None,
+        comp_hash: None,
         effective_context_window_percent: 95,
         experimental_supported_tools: Vec::new(),
     }

codex-rs/core/tests/suite/model_switching.rs

@@ -136,6 +136,7 @@ fn test_model_info(
         context_window: Some(272_000),
         max_context_window: None,
         auto_compact_token_limit: None,
+        comp_hash: None,
         effective_context_window_percent: 95,
         experimental_supported_tools: Vec::new(),
     }
@@ -957,6 +958,7 @@ async fn model_switch_to_smaller_model_updates_token_context_window() -> Result<
         context_window: Some(large_context_window),
         max_context_window: None,
         auto_compact_token_limit: None,
+        comp_hash: None,
         effective_context_window_percent,
         experimental_supported_tools: Vec::new(),
     };

codex-rs/core/tests/suite/models_cache_ttl.rs

@@ -365,6 +365,7 @@ fn test_remote_model(slug: &str, priority: i32) -> ModelInfo {
         context_window: Some(272_000),
         max_context_window: None,
         auto_compact_token_limit: None,
+        comp_hash: None,
         effective_context_window_percent: 95,
         experimental_supported_tools: Vec::new(),
         input_modalities: default_input_modalities(),

codex-rs/core/tests/suite/personality.rs

@@ -587,6 +587,7 @@ async fn remote_model_friendly_personality_instructions_with_feature() -> anyhow
         context_window: Some(128_000),
         max_context_window: None,
         auto_compact_token_limit: None,
+        comp_hash: None,
         effective_context_window_percent: 95,
         experimental_supported_tools: Vec::new(),
         input_modalities: default_input_modalities(),
@@ -701,6 +702,7 @@ async fn user_turn_personality_remote_model_template_includes_update_message() -
         context_window: Some(128_000),
         max_context_window: None,
         auto_compact_token_limit: None,
+        comp_hash: None,
         effective_context_window_percent: 95,
         experimental_supported_tools: Vec::new(),
         input_modalities: default_input_modalities(),

codex-rs/core/tests/suite/remote_models.rs

@@ -499,6 +499,7 @@ async fn remote_models_remote_model_uses_unified_exec() -> Result<()> {
         context_window: Some(272_000),
         max_context_window: None,
         auto_compact_token_limit: None,
+        comp_hash: None,
         effective_context_window_percent: 95,
         experimental_supported_tools: Vec::new(),
     };
@@ -751,6 +752,7 @@ async fn remote_models_apply_remote_base_instructions() -> Result<()> {
         context_window: Some(272_000),
         max_context_window: None,
         auto_compact_token_limit: None,
+        comp_hash: None,
         effective_context_window_percent: 95,
         experimental_supported_tools: Vec::new(),
     };
@@ -1237,6 +1239,7 @@ fn test_remote_model_with_policy(
         context_window: Some(272_000),
         max_context_window: None,
         auto_compact_token_limit: None,
+        comp_hash: None,
         effective_context_window_percent: 95,
         experimental_supported_tools: Vec::new(),
     }

codex-rs/core/tests/suite/rmcp_client.rs

@@ -1499,6 +1499,7 @@ async fn stdio_image_responses_are_sanitized_for_text_only_model() -> anyhow::Re
                 context_window: Some(272_000),
                 max_context_window: None,
                 auto_compact_token_limit: None,
+                comp_hash: None,
                 effective_context_window_percent: 95,
                 experimental_supported_tools: Vec::new(),
                 input_modalities: vec![InputModality::Text],

codex-rs/core/tests/suite/spawn_agent_description.rs

@@ -84,6 +84,7 @@ fn test_model_info(
         context_window: Some(272_000),
         max_context_window: None,
         auto_compact_token_limit: None,
+        comp_hash: None,
         effective_context_window_percent: 95,
         experimental_supported_tools: Vec::new(),
     }

codex-rs/core/tests/suite/view_image.rs

@@ -1470,6 +1470,7 @@ async fn view_image_tool_returns_unsupported_message_for_text_only_model() -> an
         context_window: Some(272_000),
         max_context_window: None,
         auto_compact_token_limit: None,
+        comp_hash: None,
         effective_context_window_percent: 95,
         experimental_supported_tools: Vec::new(),
     };