fix: preserve mode-specific model selections across mode switches

lua/opencode/core.lua

@@ -106,8 +106,6 @@ M.open = Promise.async(function(opts)
       state.last_sent_context = nil
       context.unload_attachments()
 
-      state.current_model = nil
-      state.current_mode = nil
       M.ensure_current_mode():await()
 
       state.active_session = M.create_new_session():await()
@@ -267,6 +265,12 @@ function M.configure_provider()
     local model_str = string.format('%s/%s', selection.provider, selection.model)
     state.current_model = model_str
 
+    if state.current_mode then
+      local mode_map = vim.deepcopy(state.user_mode_model_map)
+      mode_map[state.current_mode] = model_str
+      state.user_mode_model_map = mode_map
+    end
+
     if state.windows then
       ui.focus_input()
     else
@@ -456,8 +460,13 @@ M.switch_to_mode = Promise.async(function(mode)
 
   local agent_config = opencode_config and opencode_config.agent or {}
   local mode_config = agent_config[mode] or {}
-  if mode_config.model and mode_config.model ~= '' then
+
+  if state.user_mode_model_map[mode] then
+    state.current_model = state.user_mode_model_map[mode]
+  elseif mode_config.model and mode_config.model ~= '' then
     state.current_model = mode_config.model
+  elseif opencode_config and opencode_config.model and opencode_config.model ~= '' then
+    state.current_model = opencode_config.model
   end
   return true
 end)

lua/opencode/state.lua

@@ -26,6 +26,7 @@
 ---@field active_session Session|nil
 ---@field restore_points RestorePoint[]
 ---@field current_model string|nil
+---@field user_mode_model_map table<string, string>
 ---@field current_model_info table|nil
 ---@field current_variant string|nil
 ---@field messages OpencodeMessage[]|nil
@@ -76,6 +77,7 @@ local _state = {
   active_session = nil,
   restore_points = {},
   current_model = nil,
+  user_mode_model_map = {},
   current_model_info = nil,
   current_variant = nil,
   -- messages

tests/unit/core_spec.lua

@@ -481,13 +481,15 @@ describe('opencode.core', function()
             model = 'anthropic/claude-3-opus',
           },
         },
+        model = 'gpt-4',
       })
 
       stub(config_file, 'get_opencode_agents').returns(agents_promise)
       stub(config_file, 'get_opencode_config').returns(config_promise)
 
       state.current_mode = nil
       state.current_model = nil
+      state.user_mode_model_map = {}
 
       local promise = core.switch_to_mode('custom')
       local success = promise:wait()
@@ -500,57 +502,82 @@ describe('opencode.core', function()
       config_file.get_opencode_config:revert()
     end)
 
-    it('does not change current model when mode has no model configured', function()
+    it('returns false when mode is invalid', function()
+      local Promise = require('opencode.promise')
+      local agents_promise = Promise.new()
+      agents_promise:resolve({ 'plan', 'build' })
+
+      stub(config_file, 'get_opencode_agents').returns(agents_promise)
+
+      local promise = core.switch_to_mode('nonexistent')
+      local success = promise:wait()
+
+      assert.is_false(success)
+
+      config_file.get_opencode_agents:revert()
+    end)
+
+    it('returns false when mode is empty', function()
+      local promise = core.switch_to_mode('')
+      local success = promise:wait()
+      assert.is_false(success)
+
+      promise = core.switch_to_mode(nil)
+      success = promise:wait()
+      assert.is_false(success)
+    end)
+
+    it('respects user_mode_model_map priority: uses model stored in mode_model_map for mode', function()
       local Promise = require('opencode.promise')
       local agents_promise = Promise.new()
       agents_promise:resolve({ 'plan', 'build' })
       local config_promise = Promise.new()
       config_promise:resolve({
         agent = {
-          plan = {},
+          plan = { model = 'gpt-4' },
         },
+        model = 'gpt-3',
       })
-
       stub(config_file, 'get_opencode_agents').returns(agents_promise)
       stub(config_file, 'get_opencode_config').returns(config_promise)
 
       state.current_mode = nil
-      state.current_model = 'existing/model'
+      state.current_model = 'should-be-overridden'
+      state.user_mode_model_map = { plan = 'anthropic/claude-3-haiku' }
 
       local promise = core.switch_to_mode('plan')
       local success = promise:wait()
-
       assert.is_true(success)
       assert.equal('plan', state.current_mode)
-      assert.equal('existing/model', state.current_model)
+      assert.equal('anthropic/claude-3-haiku', state.current_model)
 
       config_file.get_opencode_agents:revert()
       config_file.get_opencode_config:revert()
     end)
 
-    it('returns false when mode is invalid', function()
+    it('falls back to config model if nothing else matches', function()
       local Promise = require('opencode.promise')
       local agents_promise = Promise.new()
       agents_promise:resolve({ 'plan', 'build' })
-
+      local config_promise = Promise.new()
+      config_promise:resolve({
+        agent = {
+          plan = {},
+        },
+        model = 'default-model',
+      })
       stub(config_file, 'get_opencode_agents').returns(agents_promise)
-
-      local promise = core.switch_to_mode('nonexistent')
+      stub(config_file, 'get_opencode_config').returns(config_promise)
+      state.current_mode = nil
+      state.current_model = 'old-model'
+      state.user_mode_model_map = {}
+      local promise = core.switch_to_mode('plan')
       local success = promise:wait()
-
-      assert.is_false(success)
-
+      assert.is_true(success)
+      assert.equal('plan', state.current_mode)
+      assert.equal('default-model', state.current_model)
       config_file.get_opencode_agents:revert()
-    end)
-
-    it('returns false when mode is empty', function()
-      local promise = core.switch_to_mode('')
-      local success = promise:wait()
-      assert.is_false(success)
-
-      promise = core.switch_to_mode(nil)
-      success = promise:wait()
-      assert.is_false(success)
+      config_file.get_opencode_config:revert()
     end)
   end)
 end)