implementing: require planned probes before dependent implementation

[teslamint]

Problem

Cogvault's PDF plan required a real Poppler probe before U2 implementation. The probe ran during U5 instead.
Host-specific output behavior invalidated the initial implementation and required a late deviation.

Requested change

Make implementation-time probes enforceable at their named phase in planning and implementing workflows.

Acceptance criteria

• Give each required probe an owning unit, command or procedure, expected observation, and evidence location.
• Require its evidence before dependent implementation starts.
• Record unavailable prerequisites as blocked or use a fallback already allowed by the approved plan.
• Route contradictory observations through the existing plan-change process before dependent code changes.
• Do not accept a later proof-phase run as evidence that the earlier gate ran on time.
• Add workflow regression coverage for missing, failed, contradictory, and successful probe evidence.

Evidence and scope

• Cogvault retrospective
• Approved plan

Compound-loop owns the reusable phase gate. Preserve current approval and evidence mechanisms instead of adding a separate execution framework.