[KartikP]

Use one public subject/session API across the UMI. Subject.participate(session) is the evaluation method; process() remains a concrete convenience.

Changes

• Rename evaluation calls in helpers, capabilities, memory preflight and the permanent legacy-benchmark facade. Preserve recorded driver labels.
• Expose public session, environment-diagnostic and score-reduction helpers, retaining compatibility aliases for promoted private names.
• Expose the read-only extractor mapping and modality helper used by recording tools.
• Align constructor guidance and errors with extractor, answer, policy and intervention.
• Synchronize with current v2 input-site/vector-drive documentation, preserving its annotation and forwarding test.

Validation

At e4b2828, required Linux/macOS, OpenPI and Jenkins checks pass. The coordinated installed-package run passed 954 Core tests per platform, with no skips. Core remains importable without model frameworks. These are interface/fixture checks, not a new trained-model scoring qualification.

Coordinated merge

Vision #2632, Language #437, Unified #47. All target unified-model-interface-v2. This is the agreed pre-release rename; there is no interact alias. Permanent legacy APIs remain supported. Merge only after the coordinated checks pass, then refresh Unified's peer pins to merged v2 revisions.