feat(codex): declare gpt-5.6 context window for Claude Code takeover

- Update Codex OAuth presets to the gpt-5.6 family (haiku -> gpt-5.6-luna)
  and bump the custom Codex template default model
- Inject CLAUDE_CODE_MAX_CONTEXT_TOKENS / CLAUDE_CODE_AUTO_COMPACT_WINDOW
  (372000, the ChatGPT Codex catalog window with a ~353K effective budget,
  openai/codex#31860) into effective live settings so Claude Code stops
  assuming a 200K window and compacts before the upstream rejects the prompt
- Gate the injected defaults on every configured model being gpt-5.6*:
  gpt-5.5's upstream catalog oscillates between 272K and 372K and must not
  inherit them; explicit user values always win
- Strip the injected values on switch-away backfill (mirror-inverse of the
  injection conditions) so program defaults never harden into per-provider
  explicit values, and keep both keys out of the shared common-config snippet

tests/config/claudeProviderPresets.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it } from "vitest";
 import { providerPresets } from "@/config/claudeProviderPresets";
+import { applyTemplateValues } from "@/utils/providerConfigUtils";
 
 describe("Kimi For Coding Provider Preset", () => {
   const kimiForCoding = providerPresets.find(
@@ -28,6 +29,47 @@ describe("Kimi For Coding Provider Preset", () => {
   });
 });
 
+describe("Codex Provider Preset", () => {
+  const codex = providerPresets.find((p) => p.name === "Codex");
+
+  it("should include the Codex preset", () => {
+    expect(codex).toBeDefined();
+  });
+
+  it("should override Claude Code's 200K fallback for GPT models", () => {
+    const env = (codex!.settingsConfig as any).env;
+    expect(env).toHaveProperty(
+      "CLAUDE_CODE_MAX_CONTEXT_TOKENS",
+      "${CLAUDE_CODE_MAX_CONTEXT_TOKENS}",
+    );
+    expect(env).toHaveProperty(
+      "CLAUDE_CODE_AUTO_COMPACT_WINDOW",
+      "${CLAUDE_CODE_AUTO_COMPACT_WINDOW}",
+    );
+  });
+
+  it("should expose the Codex-catalog 372K window for both context knobs", () => {
+    const values = codex!.templateValues as any;
+    expect(values?.CLAUDE_CODE_MAX_CONTEXT_TOKENS).toMatchObject({
+      defaultValue: "372000",
+      editorValue: "372000",
+    });
+    expect(values?.CLAUDE_CODE_AUTO_COMPACT_WINDOW).toMatchObject({
+      defaultValue: "372000",
+      editorValue: "372000",
+    });
+  });
+
+  it("should resolve both context placeholders into Claude Code env values", () => {
+    const config = applyTemplateValues(
+      codex!.settingsConfig,
+      codex!.templateValues,
+    ) as any;
+    expect(config.env.CLAUDE_CODE_MAX_CONTEXT_TOKENS).toBe("372000");
+    expect(config.env.CLAUDE_CODE_AUTO_COMPACT_WINDOW).toBe("372000");
+  });
+});
+
 describe("AWS Bedrock Provider Presets", () => {
   const bedrockAksk = providerPresets.find(
     (p) => p.name === "AWS Bedrock (AKSK)",