WOR-74 Preserve archive execution binding during handoff re-entry

[Ldsystem]

Summary:

• forward the complete execution binding when archive re-compiles a task brief
• use observed handoff validation only when that binding is complete
• add a regression test covering the archive re-entry contract

Root cause:
The archive path reconstructed an incomplete compile namespace, then validated without observation. The resulting validation exit was swallowed and a valid executor handoff was later reported as missing, making lifecycle cleanup take longer than the implementation it was closing.

Verification:

• full pytest suite: 670 passed
• built-in skill validation: ok
• focused workflow-contract suite: 59 passed

Linear: https://linear.app/workbundle/issue/WOR-74/archive-plan-drops-execution-binding-and-observed-handoff-evidence

[Ldsystem]

Superseded by merged PR #27 (ea15bbf). Both reviewers accepted the real archive-level mapped-evidence repair; this incomplete duplicate is not being merged.