feat(acp): add acp session events (#2938)

Author: georgeharker

doc/usage/events.md

@@ -10,6 +10,7 @@ In order to enable a tighter integration between CodeCompanion and your Neovim c
 
 The events that are fired from within the plugin are:
 
+- `CodeCompanionACPSessionPre` - Fired after ACP authentication completes but before a new session is established; allows subscribers to modify the connection (e.g. inject MCP servers) synchronously
 - `CodeCompanionChatACPModeChanged` - Fired after the ACP mode has been changed in the chat
 - `CodeCompanionChatCreated` - Fired after a chat has been created for the first time
 - `CodeCompanionChatOpened` - Fired after a chat has been opened

lua/codecompanion/acp/init.lua

@@ -24,6 +24,7 @@ local adapter_utils = require("codecompanion.utils.adapters")
 local config = require("codecompanion.config")
 local jsonrpc = require("codecompanion.utils.jsonrpc")
 local log = require("codecompanion.utils.log")
+local utils = require("codecompanion.utils")
 
 local TIMEOUTS = {
   DEFAULT = 2e4, -- 20 seconds
@@ -168,6 +169,11 @@ function Connection:connect_and_initialize()
     return nil
   end
 
+  utils.fire("ACPSessionPre", {
+    adapter_modified = self.adapter_modified,
+    agent_capabilities = self._agent_info and self._agent_info.agentCapabilities,
+  })
+
   if not self:_establish_session() then
     return nil
   end
@@ -237,6 +243,11 @@ function Connection:ensure_session()
     return false
   end
 
+  utils.fire("ACPSessionPre", {
+    adapter_modified = self.adapter_modified,
+    agent_capabilities = self._agent_info and self._agent_info.agentCapabilities,
+  })
+
   if not self:_establish_session() then
     return false
   end