fix: correct Copilot GPT-5.2 token limits

packages/opencode/src/provider/provider.ts

@@ -617,6 +617,18 @@ export namespace Provider {
   export type Info = z.infer<typeof Info>
 
   function fromModelsDevModel(provider: ModelsDev.Provider, model: ModelsDev.Model): Model {
+    const limit = iife(() => {
+      if (!provider.id.startsWith("github-copilot")) return model.limit
+      if (model.id !== "gpt-5.2" && model.id !== "gpt-5.2-codex") return model.limit
+
+      // models.dev currently reports incorrect limits for these Copilot models, causing premature compaction.
+      return {
+        ...model.limit,
+        context: 400000,
+        input: 272000,
+        output: 128000,
+      }
+    })
     const m: Model = {
       id: model.id,
       providerID: provider.id,
@@ -649,9 +661,9 @@ export namespace Provider {
           : undefined,
       },
       limit: {
-        context: model.limit.context,
-        input: model.limit.input,
-        output: model.limit.output,
+        context: limit.context,
+        input: limit.input,
+        output: limit.output,
       },
       capabilities: {
         temperature: model.temperature,

packages/opencode/test/provider/provider.test.ts

@@ -2148,3 +2148,40 @@ test("custom model with variants enabled and disabled", async () => {
     },
   })
 })
+
+test("github-copilot gpt-5.2 and gpt-5.2-codex token limits are overridden", async () => {
+  await using tmp = await tmpdir({
+    init: async (dir) => {
+      await Bun.write(
+        path.join(dir, "opencode.json"),
+        JSON.stringify({
+          $schema: "https://opencode.ai/config.json",
+        }),
+      )
+    },
+  })
+
+  await Instance.provide({
+    directory: tmp.path,
+    init: async () => {
+      Env.set("GITHUB_TOKEN", "test-token")
+    },
+    fn: async () => {
+      const providers = await Provider.list()
+      const copilot = providers["github-copilot"]
+      expect(copilot).toBeDefined()
+
+      const gpt52 = copilot.models["gpt-5.2"]
+      expect(gpt52).toBeDefined()
+      expect(gpt52.limit.context).toBe(400000)
+      expect(gpt52.limit.input).toBe(272000)
+      expect(gpt52.limit.output).toBe(128000)
+
+      const gpt52codex = copilot.models["gpt-5.2-codex"]
+      expect(gpt52codex).toBeDefined()
+      expect(gpt52codex.limit.context).toBe(400000)
+      expect(gpt52codex.limit.input).toBe(272000)
+      expect(gpt52codex.limit.output).toBe(128000)
+    },
+  })
+})