Sidecar characterization that freezes the deterministic source ordering
of the existing aggregated teaching index, cross-pack chains, and
narrative/example composer outputs. No dependency on the discourse
planner contract — this is the bridge that protects the next two
phases (ResponseMode classification + structured GroundedFact
accessors) from source-order drift.
5 tests pin: aggregated teaching index key order, cross-pack subject
and object views, narrative composer source ordering, example composer
source ordering.
Authored in worktree 3721; landed here so the main-line sequencing
(characterization -> ResponseMode -> accessors -> planner -> wiring)
can proceed against a stable substrate.
