fix(orch): observe mapped handoffs during archive-plan re-entry

[Ldsystem]

Problem

archive-plan discarded valid mapped-invariant executor results. _try_validate_task_handoff re-validated without observe=True and without forwarding --workspace-id / --execution-id / --repository-id / --execution-runtime-root. Mapped completed handoffs raised evidence-closure-blocked, the helper swallowed SystemExit, and declared plan-level acceptance was then reported as missing.

This is WOR-74. It blocked final WorkBundle archival of WOR-65 after PR #26 merged; it is not an invocation-observation implementation failure.

Fix

• For compiled evidence_capability.result: mapped briefs, archive re-entry now calls validate_executor_result_for_task(..., observe=True, **_observation_kwargs(args)).
• Non-mapped briefs keep the previous non-observing re-entry path so existing archive fixtures without execution bindings stay valid.
• set-plan-status Completed --handoff forwards the same binding arguments.

This is different from #28, which observes only when all four CLI binding flags are present. That still drops a mapped handoff for the common archive-plan --id ... path that loads the stored binding.

Tests

• test_archive_plan_accepts_mapped_invariant_handoff_with_harness_observation
• test_archive_plan_forwards_execution_binding_into_task_revalidation

Local evidence after RED (validated = [] / acceptance ... is missing):

• workflow contracts: 60 passed
• invocation + execution-context + workflow: 254 passed
• skill validator: ok: true

Full pinned suite locally: 668 passed; 1 fail / 2 errors only in test_keep_summarizing_query.py from HuggingFace SSL while downloading embeddings.

Linear

• WOR-74
• Unblocks WOR-65 archival (plan-20260830-010) after merge + rerun in the original workspace

Archive-plan re-entry test evidence

Linear Issue: WOR-65