Fixes #1728.

Summary

• Capture gbrain import <dir> target once at import start as an absolute real path, then use that canonical value for collection, checkpoint load/save, ingest logging, and git continuity.
• Write self-describing import checkpoints with schema_version: 1, owner: "gbrain", and kind: "import" while preserving safe legacy path-based checkpoint reads.
• Reject relative checkpoint dirs and wrong metadata, and document the downstream checkpoint contract in docs/guides/live-sync.md.
• Adds docs/reference/gbrain-1728-submission-package.md with the autoplan-style package matching the gstack v0.42.16.0 feat(doctor): brain health as a solved problem — cause-ranked doctor + OOM-loop line + auto-drain + pool-reap (#1685) #1802 companion.

Tests

• bun test test/import-checkpoint.test.ts (23 pass)
• bun run typecheck currently fails on pre-existing test/e2e/openclaw-plugin-load-real.test.ts:281 parameter type incompatibility, unrelated to this change.

Notes

This is the upstream prevention half of the gstack #1802 incident. gstack PR #1827 guards its own deletion boundary; this PR fixes the producer-side checkpoint identity contract.

Cross-links

• gstack PR: fix(sync): fail-closed staging-dir ownership guard — prevent rm -rf of repo (#1802) gstack#1827
• gstack issue: sync-gbrain memory stage rm -rf'd my repo root: resume path trusts checkpoint.dir without verifying it's a gstack staging dir gstack#1802
• gbrain issue: import-checkpoint.json dir can resolve to CWD/repo root on SIGTERM — enforce staging-first checkpointing #1728

Cross-links

• gstack PR: fix(sync): fail-closed staging-dir ownership guard — prevent rm -rf of repo (#1802) gstack#1827
• gstack issue: sync-gbrain memory stage rm -rf'd my repo root: resume path trusts checkpoint.dir without verifying it's a gstack staging dir gstack#1802
• gbrain issue: import-checkpoint.json dir can resolve to CWD/repo root on SIGTERM — enforce staging-first checkpointing #1728