FEAT-026: finish session command shapes and extraction boundary

[aboimpinto]

Problem

FEAT-026 is the final session-group adoption slice under EPIC-006. /structcopy still accesses concrete App state in main, and the session group’s outcomes/registration and shared helper dependency graph prevent independent crate extraction.

Intended outcome

Complete session-group adoption in place: all 17 commands compile against shared contracts and portable helpers, with concrete observation, I/O, registration and action execution outside the group. Preserve current-main behavior, including execution-identity safety. Physical relocation belongs to the later extraction step.

Refs #6145 and #5316; both broader trackers remain open.

Acceptance criteria

• AC1: Preserve command grammar, metadata, discovery, session order and human-only /structcopy availability.
• AC2: /structcopy receives exactly structcopy plus presentation authority; missing capabilities fail without actions or clipboard writes.
• AC3: All 17 session commands, helpers and portable tests compile normally without App/TUI, core/runtime services or credential-storage dependencies; shared action payloads remain portable.
• AC4: Preserve current-main selector identity, private-content omission, session ownership, unknown states, sanitization, bounds and truthful counters.
• AC5: Preserve localized stdout/native/queued/failure receipts, clipboard sequencing and session/plan/workflow state.
• AC6: Remove the completed session adoption frontier from both projections, retain unrelated pending groups, and include new crates in publication/developer tooling.
• AC7: Retain existing and newly upstreamed regressions; verify the rebased head with CI-aligned checks and the independent compilation proof. Hosted checks must pass before owner review; complete Devin Review and resolve actionable findings before owner review. The contributor corrected the earlier Greptile requirement because Greptile is unavailable here.

Paulo Aboim Pinto