Clear missing orphaned worktree mappings

[yvette-carlisle]

Summary

• Clear runtime-provenance worktree mappings during live reconciliation when the checkout path is missing and no lease, active label, needs-attention label, shared claim, running attempt, or review handoff marker owns the lane.
• Keep legacy_unknown mappings on the explicit legacy closeout audit path.
• Add a Program reconciler regression test proving stale missing mappings no longer occupy conflict domains after reconciliation.
• Update the runtime spec for the missing-orphan cleanup contract.

Validation

• cargo make fmt
• cargo make fmt-check
• cargo test -p decodex program_reconciler --all-features
• cargo test -p decodex reconciliation --all-features
• cargo make check-rust
• cargo make check-vstyle
• cargo make test (1200 passed, 1 skipped)

Runtime evidence

• Ran the fixed binary against the registered decodex project.
• The stale XY-971 mapping was cleared and XY-971 is now a current lane: run_id xy-971-attempt-1-1781660047, current_operation agent_run.