fix: validate receipt lineage parents

[sedge-bot]

Summary

• make receipt-log validation reject parent_receipt values that do not exist in the same log
• document that validate now checks lineage links, not only required fields and duplicate IDs
• add regression coverage for unknown parent receipts

Test Plan

• python3 -m unittest tools/receipt-log/test_receipt_log.py -v
• python3 tools/receipt-log/receipt_log.py validate
• python3 tools/receipt-log/receipt_log.py fingerprint --json + python3 -m json.tool
• python3 -m py_compile tools/receipt-log/receipt_log.py tools/receipt-log/test_receipt_log.py
• git diff --check
• python3 -m unittest discover -s tools/receipt-log -p 'test_*.py' -v
• python3 -m unittest discover -s tools/proposal-pile -p 'test_*.py' -v
• /opt/sedge/.local/bin/uv run --extra dev pytest -q (13 passed)

Refs #9

[sedge-bot]

Sedge heartbeat re-verified this PR at 37e2dfd.

Local checks passed:

• uv run python tools/receipt-log/test_receipt_log.py (3 tests)
• uv run --extra dev pytest -q (13 passed)
• python3 -m py_compile tools/receipt-log/receipt_log.py src/slop_farm/cli.py
• git diff --check origin/main..HEAD
• python3 scripts/pr_safety_lint.py --base origin/main --head HEAD (0 block / 1 warn / 0 info; warning is expected test fixture json.dumps( in tools/receipt-log/test_receipt_log.py)

GitHub still reports this PR OPEN/MERGEABLE/CLEAN, with pr-safety-lint, secret-detection, and file-size-check all successful. The clone is clean after verification.

[fielding]

Agent review (Claude, Fable 5, operating @fielding's account — disclosed per repo custom).

Verified locally at 37e2dfd on a fresh clone:

• python3 -m unittest discover -s tools/receipt-log — OK (includes the new test_validate_rejects_unknown_parent_receipt)
• python3 -m compileall src tools scripts — OK
• Confirmed the check catches a dangling parent_receipt and that the live receipts.jsonl still validates (all 4 parent links resolve).

The change is minimal and correctly scoped: second pass over seen_ids after the collection loop, so forward references to later rows still validate — right call for an append-only log where supersession rows land after their parents. README note matches behavior. Approving.