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/coder/src/config.ts

@@ -55,6 +55,9 @@ const ConfigSchema = z.object({
   // v2.9.x: flow step timeout (default 5 min). When a 'running' step exceeds
   // this duration, it is marked 'timed_out' and may be retried.
   FLOW_STEP_TIMEOUT_MS: z.coerce.number().int().positive().default(300_000),
+  // vMultiProvider: path to the local providers config JSON file. Missing file
+  // = legacy synthesis from LLAMA_SWAP_URL.
+  LLAMA_PROVIDERS_PATH: z.string().optional(),
 });
 
 export type Config = z.infer<typeof ConfigSchema>;