[zzwong]

Scope

Refs #178. Service-only foundation building on merged #187; the broader issue remains incomplete.

• Move discussion DTOs into core with serialization and adapter compatibility re-exports; preserve opaque IDs, participants, contributor identities, timestamps, optional etags and raw finding metadata.
• Add default-unsupported provider/workbench list and lazy-detail methods; Entire delegates to its existing bounded, identity-checking reader.
• Dispatch under the existing read permit, reject cancellation before/after invocation, and return results without snapshot/store writes.

Verification

• Two new focused offline service integration tests passed: fake CLI dispatch, lazy detail, serialization, pre-cancellation without CLI calls, late list cancellation rejection, unsupported detail, denied versus empty, and no recent snapshot creation.
• One existing discussion metadata regression passed after moving DTO parsing.
• All-target adapters Clippy with warnings denied, all-target UI cargo check, fmt and diff checks passed.
• Independent static review is clear. Existing raw-byte transport unchanged; its suite was not redundantly rerun.

Explicit limits

No UI controls, completion-generation state, transcript import, persistence/resume or new snapshot schema. UI callers still need exact session/generation and pinned-identity guards, including same-head refresh. No new concurrent-permit saturation test or UI completion-race qualification; cancellation is checked before/after reads, not a claim of transactional cancellation. No live Entire/native GUI verification. No verified inline anchor or approval/merge-readiness claim.