fix: report errors on promise:wait failures

I ran into an issue where I'd messed up my opencode config and I was
getting unhelpful "Error executing vim.schedule lua callback: [NULL]"
errors.

The combo of promises and pcalls is kind of gross but it's better to
report the errors than swallow them and surface unhelpful, generic
errors.

Author: cameronr

lua/opencode/config_file.lua

@@ -10,7 +10,16 @@ function M.get_opencode_config()
     local state = require('opencode.state')
     M.config_promise = state.api_client:get_config()
   end
-  return M.config_promise:wait() --[[@as OpencodeConfigFile|nil]]
+  local ok, result = pcall(function()
+    return M.config_promise:wait()
+  end)
+
+  if not ok then
+    vim.notify('Error fetching Opencode config: ' .. vim.inspect(result), vim.log.levels.ERROR)
+    return nil
+  end
+
+  return result --[[@as OpencodeConfigFile|nil]]
 end
 
 ---@return OpencodeProject|nil
@@ -19,7 +28,15 @@ function M.get_opencode_project()
     local state = require('opencode.state')
     M.project_promise = state.api_client:get_current_project()
   end
-  return M.project_promise:wait() --[[@as OpencodeProject|nil]]
+  local ok, result = pcall(function()
+    return M.project_promise:wait()
+  end)
+  if not ok then
+    vim.notify('Error fetching Opencode project: ' .. vim.inspect(result), vim.log.levels.ERROR)
+    return nil
+  end
+
+  return result --[[@as OpencodeProject|nil]]
 end
 
 ---@return OpencodeProvidersResponse|nil
@@ -28,7 +45,15 @@ function M.get_opencode_providers()
     local state = require('opencode.state')
     M.providers_promise = state.api_client:list_providers()
   end
-  return M.providers_promise:wait() --[[@as OpencodeProvidersResponse|nil]]
+  local ok, result = pcall(function()
+    return M.providers_promise:wait()
+  end)
+  if not ok then
+    vim.notify('Error fetching Opencode providers: ' .. vim.inspect(result), vim.log.levels.ERROR)
+    return nil
+  end
+
+  return result --[[@as OpencodeProvidersResponse|nil]]
 end
 
 function M.get_model_info(provider, model)

lua/opencode/session.lua

@@ -43,9 +43,16 @@ end
 ---@return Session[]|nil
 function M.get_all_sessions()
   local state = require('opencode.state')
-  local sessions = state.api_client:list_sessions():wait()
+  local ok, result = pcall(function()
+    return state.api_client:list_sessions():wait()
+  end)
+
+  if not ok then
+    vim.notify('Failed to fetch session list: ' .. vim.inspect(result), vim.log.levels.ERROR)
+    return nil
+  end
 
-  return vim.tbl_map(M.create_session_object, sessions)
+  return vim.tbl_map(M.create_session_object, result --[[@as Session[] ]])
 end
 
 ---Create a Session object from JSON