Add adapter session codecs with cwd-aware resume and unknown-session retry

Introduce AdapterSessionCodec interface for structured session serialization,
deserialization, and display ID extraction. Implement codecs for claude_local
and codex_local adapters with cwd validation — sessions saved for a different
working directory are not resumed. Both adapters now return sessionParams and
sessionDisplayId alongside legacy sessionId.

Add isCodexUnknownSessionError detection and automatic retry with fresh session
for codex_local (matching existing claude_local behavior). Inject approval
context env vars (PAPERCLIP_APPROVAL_ID, PAPERCLIP_APPROVAL_STATUS,
PAPERCLIP_LINKED_ISSUE_IDS) into adapter environments.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/adapters/index.ts

@@ -4,6 +4,7 @@ export type {
   AdapterExecutionContext,
   AdapterExecutionResult,
   AdapterInvocationMeta,
+  AdapterSessionCodec,
   UsageSummary,
   AdapterAgent,
   AdapterRuntime,