chore: snapshot working tree - pty_exited notifications + in-flight inference WIP

feat(booterm): structured pty_exited WS notifications. Plan-validated, impl-validated, code-reviewed green (contracts build clean, contracts test 29/29, booterm + web typecheck clean).

wip: in-progress inference/provider refactor (agents.ts, provider.ts, new llama-providers.ts, removed llama-args-validator), plus arena, dispatcher, compaction, schema changes.

openspec: pty-exit-notifications complete; x-agent-flags planned (not yet implemented).

apps/web/src/hooks/terminal/useTerminalSocket.ts

@@ -234,6 +234,17 @@ export function useTerminalSocket({
             t.write(`\r\n\x1b[2m[process exited with code ${frame.code}]\x1b[0m\r\n`);
             return;
           }
+          if (frame?.type === 'pty_exited') {
+            if (frame.timed_out) {
+              t.write('\r\n\x1b[2m[process timed out and was killed]\x1b[0m\r\n');
+            } else {
+              t.write(`\r\n\x1b[2m[process exited with code ${frame.exit_code}]\x1b[0m\r\n`);
+            }
+            if (frame.last_lines.length > 0) {
+              t.write(frame.last_lines[frame.last_lines.length - 1] + '\r\n');
+            }
+            return;
+          }
           t.write(e.data);
         } else {
           t.write(new Uint8Array(e.data as ArrayBuffer));