port goose2 chat attachments into goose

ui/goose2/scripts/check-file-sizes.mjs

@@ -65,6 +65,11 @@ const EXCEPTIONS = {
     justification:
       "Session prepare/load/list logic, working-dir updates, wait_for_replay_drain helper with iteration cap, and composite prepared-session reuse remain colocated while ACP session ownership stabilizes.",
   },
+  "src-tauri/src/commands/system.rs": {
+    limit: 620,
+    justification:
+      "Desktop system commands still centralize file mentions, attachment inspection, platform-aware path dedupe, guarded image loading, and export helpers in one Tauri command surface.",
+  },
 };
 
 // Directories excluded from size checks (imported library code)

ui/goose2/src-tauri/Cargo.toml

@@ -40,6 +40,8 @@ tokio-tungstenite = "0.21.0"
 acp-client = { git = "https://github.com/block/builderbot", rev = "db184d20cb48e0c90bbd3fea4a4a871fc9d8a6ad" }
 doctor = { git = "https://github.com/block/builderbot", rev = "8e1c3ec145edc0df5f04b4427cfd758378036862" }
 ignore = "0.4.25"
+base64 = "0.22"
+mime_guess = "2"
 
 [target.'cfg(target_os = "macos")'.dependencies]
 keyring = { version = "3", features = ["apple-native"] }