Claude agent: support SDK-native session persistence and resume across VM restarts

Request

Make "persist a Claude session and resume it later, across VM restarts" a supported path for the packaged Claude agent:

1. AgentOs.resumeSession() should perform an SDK-native resume (ACP session/load → SDK resume), restoring full session state (context, tool state, compaction) from the persisted session file — not a "new session + transcript preamble" fallback.
2. Session persistence should be enabled (or enableable) in the packaged adapter, and CLAUDE_CODE_SKIP_INITIAL_MESSAGES must not be forced in a way that breaks resumed-session replay.
3. Document how to place the Claude session/config directory (CLAUDE_CONFIG_DIR) on durable storage so persisted sessions survive VM restarts.

The current adapter advertises sessionCapabilities.resume — if the above already works end-to-end, a documented statement plus a regression test would be enough to close this.

Why

Resume built from replayed transcripts is not equivalent to SDK-native resume: it loses compaction state and tool state, and re-sends the full history as prompt input. For any long-lived conversation spanning more than one VM lifetime, native persistence + resume is the only correct primitive.

Start by tracing AgentOs.resumeSession() through the ACP session/load and SDK resume path, then inspect how the packaged adapter handles persistence and CLAUDE_CODE_SKIP_INITIAL_MESSAGES. Verify whether CLAUDE_CONFIG_DIR can be placed on durable storage and add or run a regression test covering resume across VM restarts; done means native state, including context, tool state, and compaction, is restored.