feat(providers): add ChatGPT/Codex subscription OAuth (PKCE + account-id, hardcoded catalog)

29th platform `openai-codex` (uses_oauth, Responses wire). PKCE-localhost login at
auth.openai.com (client app_EMoamEEZ73f0CkXaXp7hrann, redirect localhost:1455/auth/
callback, form token exchange, fresh-random state) reusing the claude-pro-max flow;
OAuthFlow::PkceLocalhost gained a redirect_path and OAuthConfig an authorize_extra
(empty elsewhere, so claude/xai/copilot authorize URLs stay byte-identical).

Codex-specific: the access token is a JWT carrying chatgpt_account_id, which becomes
the `chatgpt-account-id` inference header. It is derived STATELESSLY from whichever
bearer rides each request (so a rotated token needs no persisted field), and BOTH
login and refresh fail fast when the claim is absent — gated on the explicit
OAuthConfig.requires_chatgpt_account_id fact, never inferred from the token-body
encoding (a plain form endpoint is the OAuth norm and must not inherit this).

Inference rides the existing Responses wire at chatgpt.com/backend-api/codex →
/responses, with codex headers (chatgpt-account-id, originator, OpenAI-Beta
responses=experimental, codex UA) gated on SamplerConfig.openai_codex so API-key
`openai` stays byte-identical; store:false was already the global Responses default.

Catalog is HARDCODED (no live endpoint exists for this backend; read from the
official Codex CLI's model cache): gpt-5.6-sol/terra/luna + gpt-5.5, ctx 272000,
each with its real reasoning levels (low..ultra — ReasoningEffort gained Ultra).
Excluded: gpt-5.3-codex-spark (supported_in_api=false), gpt-5.4/-mini and
codex-auto-review (hidden) — they would list but fail at inference. The fetch
short-circuits before any HTTP; Kigi never shells out to the codex CLI or reads
~/.codex.

Security review fixes: redact any `account-id` header from request logs (it was
reaching debug logs), strict 3-segment JWT check (fail closed), refresh no longer
fails open on a missing claim. Inherits leak-safe pooled routing (scope
oauth/openai-codex) — never the Kimi token. Full gate green (234 suites, 0 warnings).

crates/codegen/kigi-shell/src/session/acp_session_impl/sampler_turn.rs

@@ -283,6 +283,16 @@ impl SessionActor {
         kigi_models::parse_managed_model_key(managed_key.as_deref().unwrap_or(model))
             .is_some_and(|(platform, _)| platform.sends_copilot_editor_headers())
     }
+    /// Whether `model` routes to the ChatGPT/Codex Responses platform
+    /// (openai-codex) — the gate for the sampler's Codex identity headers
+    /// (`chatgpt-account-id` + originator + OpenAI-Beta). Every other model
+    /// returns `false`, keeping the API-key `openai` Responses request
+    /// byte-identical.
+    fn model_is_openai_codex(&self, model: &str) -> bool {
+        let managed_key = self.managed_key_for_model(model);
+        kigi_models::parse_managed_model_key(managed_key.as_deref().unwrap_or(model))
+            .is_some_and(|(platform, _)| platform.sends_codex_responses_headers())
+    }
     /// LEAK guard for the stamped aux paths (auto-mode classifier, image
     /// describe). After [`crate::agent::config::stamp_session_local_sampler_fields`]
     /// has copied the SESSION model's `bearer_resolver` onto an aux
@@ -394,6 +404,8 @@ impl SessionActor {
         let anthropic_oauth = self.model_is_anthropic_oauth(&cfg.model);
         // GitHub Copilot editor-identity headers for THIS turn's model.
         let github_copilot = self.model_is_github_copilot(&cfg.model);
+        // ChatGPT/Codex identity headers for THIS turn's model.
+        let openai_codex = self.model_is_openai_codex(&cfg.model);
         let auth_scheme = model_facts.auth_scheme;
         let mut extra_headers = cfg.extra_headers;
         crate::agent::config::inject_url_derived_headers(
@@ -436,6 +448,7 @@ impl SessionActor {
             auth_scheme,
             anthropic_oauth,
             github_copilot,
+            openai_codex,
             chat_compat: cfg.chat_compat,
             extra_headers,
             context_window: cfg.context_window.get(),

crates/codegen/kigi-shell/src/session/acp_session_tests/auth_error_no_retry_tests.rs

@@ -851,6 +851,7 @@ async fn set_session_model_invalidates_byok_memo_for_same_model_id() {
                 auth_scheme: Default::default(),
                 anthropic_oauth: false,
                 github_copilot: false,
+                openai_codex: false,
                 extra_headers: Default::default(),
                 context_window: 256_000,
                 force_http1: false,

crates/codegen/kigi-shell/src/session/acp_session_tests/cancel_running_task_tests.rs

@@ -48,6 +48,7 @@ async fn persist_ack_waits_for_disk_flush_before_success() {
                 auth_scheme: Default::default(),
                 anthropic_oauth: false,
                 github_copilot: false,
+                openai_codex: false,
                 extra_headers: Default::default(),
                 context_window: 100_000,
                 force_http1: false,
@@ -346,6 +347,7 @@ async fn first_turn_memory_injection_persists_to_chat_history() {
                 auth_scheme: Default::default(),
                 anthropic_oauth: false,
                 github_copilot: false,
+                openai_codex: false,
                 context_window: 100_000,
                 force_http1: false,
                 max_retries: None,
@@ -478,6 +480,7 @@ async fn first_turn_memory_injection_disabled_does_not_persist_to_chat_history()
                 auth_scheme: Default::default(),
                 anthropic_oauth: false,
                 github_copilot: false,
+                openai_codex: false,
                 context_window: 100_000,
                 force_http1: false,
                 max_retries: None,
@@ -1748,6 +1751,7 @@ async fn cancel_propagates_to_sampler_handle_so_no_further_emission() {
                 auth_scheme: Default::default(),
                 anthropic_oauth: false,
                 github_copilot: false,
+                openai_codex: false,
                 extra_headers: Default::default(),
                 context_window: 100_000,
                 force_http1: false,

crates/codegen/kigi-shell/src/session/helpers/session_compact.rs

@@ -1592,6 +1592,7 @@ mod reasoning_compaction_regression_tests {
             auth_scheme: Default::default(),
             anthropic_oauth: false,
             github_copilot: false,
+            openai_codex: false,
             extra_headers: Default::default(),
             context_window: 256_000,
             force_http1: false,