fix: Codespaces — skip GITHUB_TOKEN auto-enable for github-models, cap retries, fix phantom command

Closes #413

- Skip auto-enabling `github-models` and `github-copilot` providers when
  `CODESPACES=true` and only `GITHUB_TOKEN` is available (the Codespace
  machine token lacks model-inference permissions, causing immediate 429s)
- Cap retry attempts at 5 (`RETRY_MAX_ATTEMPTS`) to prevent infinite
  retry loops with 30+ minute backoff
- Replace phantom `/discover-and-add-mcps` toast with actionable message
  ("Ask the assistant to add them")
- Add `.devcontainer/` config (Node 22, Bun 1.3.10) for reproducible
  Codespace environments
- Update docs to reference `mcp_discover` tool instead of non-existent
  slash command

Author: anandgupta42

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

@@ -2330,4 +2330,28 @@ test("github-models is available when GITHUB_TOKEN set without CODESPACES", asyn
     },
   })
 })
+
+test("github-copilot is excluded when CODESPACES=true and only GITHUB_TOKEN is set", async () => {
+  await using tmp = await tmpdir({
+    init: async (dir) => {
+      await Bun.write(
+        path.join(dir, "opencode.json"),
+        JSON.stringify({
+          $schema: "https://altimate.ai/config.json",
+        }),
+      )
+    },
+  })
+  await Instance.provide({
+    directory: tmp.path,
+    init: async () => {
+      Env.set("GITHUB_TOKEN", "ghu_fake_codespace_token")
+      Env.set("CODESPACES", "true")
+    },
+    fn: async () => {
+      const providers = await Provider.list()
+      expect(providers["github-copilot"]).toBeUndefined()
+    },
+  })
+})
 // altimate_change end

packages/opencode/test/session/retry.test.ts

@@ -92,10 +92,8 @@ describe("session.retry.delay", () => {
 })
 
 describe("session.retry.max_attempts", () => {
-  test("RETRY_MAX_ATTEMPTS is defined and reasonable", () => {
-    expect(SessionRetry.RETRY_MAX_ATTEMPTS).toBeDefined()
-    expect(SessionRetry.RETRY_MAX_ATTEMPTS).toBeGreaterThanOrEqual(3)
-    expect(SessionRetry.RETRY_MAX_ATTEMPTS).toBeLessThanOrEqual(10)
+  test("RETRY_MAX_ATTEMPTS is 5", () => {
+    expect(SessionRetry.RETRY_MAX_ATTEMPTS).toBe(5)
   })
 })