fix: harden Codex automatic archive

[fengseekling-coder]

Summary

• follow Codex CODEX_HOME as the single default root across macOS and Windows
• reconcile both generated_images files and incremental sessions JSONL events
• recover image-generation results from session payloads only when the standard file is missing
• keep session recovery inside MOSA-managed staging without widening trusted filesystem roots
• keep standard-file hardlink behavior separate from recovered session copies
• add regression coverage for incremental session indexing, recovery, dedupe, runtime path consistency, and hardlink boundaries

Release

Prepares 0.2.1-rc.13. The branch tree is byte-for-byte identical to the locally verified final tree 78f8498d1d453b59579035aa6d57e1eca2ab8173.

Local verification

• build: pass
• lint: pass
• check: pass
• focused Codex/runtime tests: pass
• full test suite: pass before final test-only split; isolated hardlink regression: pass after split
• working tree: clean

CI should run the repository's normal verify/macOS/Windows gates before merge.