[Codex][CLI] Gate image inputs by model modalities (#10271)

###### Summary

- Add input_modalities to model metadata so clients can determine
supported input types.
- Gate image paste/attach in TUI when the selected model does not
support images.
- Block submits that include images for unsupported models and show a
clear warning.
- Propagate modality metadata through app-server protocol/model-list
responses.
  - Update related tests/fixtures.

  ###### Rationale

  - Models support different input modalities.
- Clients need an explicit capability signal to prevent unsupported
requests.
- Backward-compatible defaults preserve existing behavior when modality
metadata is absent.

  ###### Scope

  - codex-rs/protocol, codex-rs/core, codex-rs/tui
  - codex-rs/app-server-protocol, codex-rs/app-server
  - Generated app-server types / schema fixtures

  ###### Trade-offs

- Default behavior assumes text + image when field is absent for
compatibility.
  - Server-side validation remains the source of truth.

  ###### Follow-up

- Non-TUI clients should consume input_modalities to disable unsupported
attachments.
- Model catalogs should explicitly set input_modalities for text-only
models.

  ###### Testing

  - cargo fmt --all
  - cargo test -p codex-tui
  - env -u GITHUB_APP_KEY cargo test -p codex-core --lib
  - just write-app-server-schema
- cargo run -p codex-cli --bin codex -- app-server generate-ts --out
app-server-types
  - test against local backend
  
<img width="695" height="199" alt="image"
src="https://github.com/user-attachments/assets/d22dd04f-5eba-4db9-a7c5-a2506f60ec44"
/>

---------

Co-authored-by: Josh McKinney <joshka@openai.com>

codex-rs/protocol/src/openai_models.rs

@@ -1,3 +1,8 @@
+//! Shared model metadata types exchanged between Codex services and clients.
+//!
+//! These types are serialized across core, TUI, app-server, and SDK boundaries, so field defaults
+//! are used to preserve compatibility when older payloads omit newly introduced attributes.
+
 use std::collections::HashMap;
 use std::collections::HashSet;
 
@@ -43,6 +48,38 @@ pub enum ReasoningEffort {
     XHigh,
 }
 
+/// Canonical user-input modality tags advertised by a model.
+#[derive(
+    Debug,
+    Serialize,
+    Deserialize,
+    Clone,
+    Copy,
+    PartialEq,
+    Eq,
+    Display,
+    JsonSchema,
+    TS,
+    EnumIter,
+    Hash,
+)]
+#[serde(rename_all = "lowercase")]
+#[strum(serialize_all = "lowercase")]
+pub enum InputModality {
+    /// Plain text turns and tool payloads.
+    Text,
+    /// Image attachments included in user turns.
+    Image,
+}
+
+/// Backward-compatible default when `input_modalities` is omitted on the wire.
+///
+/// Legacy payloads predate modality metadata, so we conservatively assume both text and images are
+/// accepted unless a preset explicitly narrows support.
+pub fn default_input_modalities() -> Vec<InputModality> {
+    vec![InputModality::Text, InputModality::Image]
+}
+
 /// A reasoning effort option that can be surfaced for a model.
 #[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema, PartialEq, Eq)]
 pub struct ReasoningEffortPreset {
@@ -88,6 +125,9 @@ pub struct ModelPreset {
     pub show_in_picker: bool,
     /// whether this model is supported in the api
     pub supported_in_api: bool,
+    /// Input modalities accepted when composing user turns for this preset.
+    #[serde(default = "default_input_modalities")]
+    pub input_modalities: Vec<InputModality>,
 }
 
 /// Visibility of a model in the picker or APIs.
@@ -206,6 +246,9 @@ pub struct ModelInfo {
     #[serde(default = "default_effective_context_window_percent")]
     pub effective_context_window_percent: i64,
     pub experimental_supported_tools: Vec<String>,
+    /// Input modalities accepted by the backend for this model.
+    #[serde(default = "default_input_modalities")]
+    pub input_modalities: Vec<InputModality>,
 }
 
 impl ModelInfo {
@@ -350,6 +393,7 @@ impl From<ModelInfo> for ModelPreset {
             }),
             show_in_picker: info.visibility == ModelVisibility::List,
             supported_in_api: info.supported_in_api,
+            input_modalities: info.input_modalities,
         }
     }
 }
@@ -460,6 +504,7 @@ mod tests {
             auto_compact_token_limit: None,
             effective_context_window_percent: 95,
             experimental_supported_tools: vec![],
+            input_modalities: default_input_modalities(),
         }
     }