refactor(coding-agent): replace AgentSessionRuntimeHost with closure-based AgentSessionRuntime

- Replace AgentSessionRuntimeHost and bootstrap abstractions with AgentSessionRuntime
- Runtime creation is now closure-based via CreateAgentSessionRuntimeFactory
- Factory closes over process-global fixed inputs, recreates cwd-bound services per effective cwd
- Session config (model, thinking, tools, scoped models) re-resolved per target cwd
- CLI resource paths resolved once at startup as absolute paths
- Swap lifecycle: teardown old, create next, apply next (hard fail on creation error)
- Unified diagnostics model (info/warning/error) for args, services, session resolution, resources
- No logging or process exits inside creation/parsing logic
- Removed session_directory support
- Removed session_switch and session_fork extension events (use session_start with reason)
- Moved package/config CLI to package-manager-cli.ts
- Fixed theme init for --resume session picker
- Fixed flaky reftable footer test (content-based polling)
- Fixed silent drop of unknown single-dash CLI flags
- Added error diagnostics for missing explicit CLI resource paths
- Updated SDK docs, examples, plans, exports, tests, changelog

fixes #2753

packages/coding-agent/src/core/index.ts

@@ -12,11 +12,19 @@ export {
 	type SessionStats,
 } from "./agent-session.js";
 export {
-	type AgentSessionRuntimeBootstrap,
-	AgentSessionRuntimeHost,
-	type CreateAgentSessionRuntimeOptions,
+	AgentSessionRuntime,
+	type CreateAgentSessionRuntimeFactory,
+	type CreateAgentSessionRuntimeResult,
 	createAgentSessionRuntime,
 } from "./agent-session-runtime.js";
+export {
+	type AgentSessionRuntimeDiagnostic,
+	type AgentSessionServices,
+	type CreateAgentSessionFromServicesOptions,
+	type CreateAgentSessionServicesOptions,
+	createAgentSessionFromServices,
+	createAgentSessionServices,
+} from "./agent-session-services.js";
 export { type BashExecutorOptions, type BashResult, executeBash, executeBashWithOperations } from "./bash-executor.js";
 export type { CompactionResult } from "./compaction/index.js";
 export { createEventBus, type EventBus, type EventBusController } from "./event-bus.js";