Contract-only landing for the typed multi-move discourse layer that
will sit between grounding and graph construction:
DialogueIntent + ResponseMode + GroundingBundle
-> DiscoursePlan
-> PropositionGraph
-> ArticulationTarget
-> RealizedPlan
Adds frozen dataclasses (ResponseMode, FactSource, GroundedFact,
GroundingBundle, DiscourseMoveKind, DiscourseMove, DiscoursePlan),
canonical sort + as_dict + to_json serialization (sorted keys,
no-whitespace separators), and the pure plan_discourse signature
(raises NotImplementedError; move-selection rules deferred).
23 contract tests pin the determinism invariants required before
DiscoursePlan can be folded into compute_trace_hash in a follow-up
ADR: frozen-dataclass equality, canonical pack<teaching<vault<operator
ordering, byte-stable to_json across calls and equal plans, JSON
round-trip stability, and signature purity (no chat.* imports, no
clock/env/filesystem reads).
No runtime wiring; smoke suite 67/67; cognition eval byte-identical
(public 100/100/91.7/100, holdout 100/100/83.3/100).
