fix(session): route all Muse family models to the Meta system prompt (#41581)

packages/opencode/src/session/prompt/meta.txt

@@ -1,4 +1,4 @@
-You are OpenCode, a coding agent that helps users with software engineering tasks. You are powered by Muse Spark, a large language model trained by Meta MSL.
+You are OpenCode, a coding agent that helps users with software engineering tasks. You are powered by {{MODEL_NAME}}, a large language model trained by Meta MSL.
 
 Use the instructions below and the tools available to assist the user.
 
@@ -61,5 +61,5 @@ Use the instructions below and the tools available to assist the user.
 - NEVER use comments as a place for long-winded chain-of-thought. Long thinking texts must be generated as private reasoning. Comments in code must be appropriately concise.
 
 # User Help & Feedback
-- Users can give feedback or report issues at https://github.com/anomalyco/opencode and mention that they are using Meta Muse Spark.
+- Users can give feedback or report issues at https://github.com/anomalyco/opencode and mention that they are using Meta {{MODEL_NAME}}.
 - When users ask directly about OpenCode (eg. "can OpenCode do...", "are you able to do...") or its features (eg. implement a hook, write a slash command, or install an MCP server), use the WebFetch tool to gather information to answer the question from the OpenCode docs at https://opencode.ai/docs.

packages/opencode/src/session/system.ts

@@ -25,7 +25,10 @@ import { MCP } from "@/mcp"
 import { PermissionV1 } from "@opencode-ai/core/v1/permission"
 
 export function provider(model: Provider.Model) {
-  if (model.api.id.includes("muse-spark")) return [PROMPT_META]
+  if (model.api.id.includes("muse")) {
+    const name = model.api.id.includes("muse-glimmer") ? "Muse Glimmer" : "Muse Spark"
+    return [PROMPT_META.replaceAll("{{MODEL_NAME}}", name)]
+  }
   if (model.api.id.includes("gpt-4") || model.api.id.includes("o1") || model.api.id.includes("o3"))
     return [PROMPT_BEAST]
   if (model.api.id.includes("gpt")) {

packages/opencode/test/session/system.test.ts

@@ -85,9 +85,21 @@ const it = testEffect(
 
 describe("session.system", () => {
   test("selects the Meta prompt for Muse Spark model IDs", () => {
-    expect(SystemPrompt.provider({ api: { id: "meta/muse-spark-preview" } } as Provider.Model)[0]).toContain(
-      "Meta Muse Spark",
-    )
+    for (const id of ["meta/muse-spark-preview", "muse-spark-1.1", "muse-spark-1.2"]) {
+      const prompt = SystemPrompt.provider({ api: { id } } as Provider.Model)[0]
+      expect(prompt).toContain("powered by Muse Spark,")
+      expect(prompt).toContain("using Meta Muse Spark.")
+      expect(prompt).not.toContain("{{MODEL_NAME}}")
+    }
+  })
+
+  test("selects the Meta prompt for Muse Glimmer model IDs", () => {
+    for (const id of ["meta/muse-glimmer", "meta/muse-glimmer-30b", "muse-glimmer-30b"]) {
+      const prompt = SystemPrompt.provider({ api: { id } } as Provider.Model)[0]
+      expect(prompt).toContain("powered by Muse Glimmer,")
+      expect(prompt).toContain("using Meta Muse Glimmer.")
+      expect(prompt).not.toContain("{{MODEL_NAME}}")
+    }
   })
 
   it.effect("skills output is sorted by name and stable across calls", () =>