Make chunked plans own dependency graphs (Task G4)

[asinghvi17]

Task G4 of regrid-notes/2026-08-21-regridding-simplification-plan.md, Phase 2 — the last card of the phase. Stacked on #71 (which is stacked on #70); base is claude/g3-graph-identity, not main and not claude/perf-ladder.

Record: regrid-notes/2026-08-23-g4-plan-owns-graph.md.

What landed

ChunkedPlan gains one field and the module one accessor:

struct ChunkedPlan{...,G<:Union{Nothing,ChunkDependencyGraph}}
    ...
    dependencies::G
end
dependencies(plan::ChunkedPlan) = plan.dependencies   # builds nothing

The relation is chosen once, at construction:

dependencies	plan holds	construction cost
nothing (default)	none	nothing at all — a dedicated method returns without even calling support_radius
true	one built here, at the plan's own radius	one chunk_dependency_graph
a ChunkDependencyGraph	that object, by reference	two spacestamp calls, after validate_dependencies
false	none, explicitly	nothing; rejects a stray refine/narrow

refine/narrow are keywords of lazy plan_regrid (and the ChunkedPlan constructor it forwards to) and of nothing else. chunk_dependency_graph(plan; refine, narrow) is deleted; the space form lost both keywords; the narrow phase moved to a private _builddependencies that only plan construction calls. regrid/regrid! take none. chunkgraph.jl now precedes plans.jl in the include order.

connectedchunkpairs is deleted — since #69 it ran line for line the loop _chunkgraph runs to fill its rows. Its one assertion in test_lazy.jl now reads the graph's own rows.

Phase 2 gate, as tests

one logical plan exposes exactly one validated relation, and a narrow phase cannot be supplied after the plan exists

Four new testsets, 62 assertions. The "not after the fact" half is a method error, not a runtime throw: Base.kwarg_decl over every method of chunk_dependency_graph, restrict, regrid and regrid! shows refine/narrow absent and over plan_regrid shows them present; methods(chunk_dependency_graph, Tuple{ChunkedPlan}) is empty; the field is on an immutable struct. "Exactly one" is proved with a probe space that counts every chunktree call: 0 after a default plan, and unchanged by five dependencies calls on a plan that owns one.

Production

scripts/copdem_production.jl:764 — the call site this card exists to remove — is gone. dagplan constructs the global ChunkedPlan with dependencies = true and the narrow phase, and reads GR.dependencies(globalplan); the driver gained check("the graph is the global plan's own relation", ...). [measured] on the real GLO-90 × IGeo7-L12 pair: 326 064 edges, equal DependencyIdentity, 0.118 s warm — identical to before.

Per-column plans own none, and the card's "share a row view" is not possible at this shape — regrid_chunk's destination is a rooted one-chunk subtree grid, a different space from the 66 175-chunk PartialGrid a row view stamps, so validate_dependencies refuses it (correctly). [measured], benchmark/plan_dependency_ownership.jl, 25 columns × 5 samples:

per-column arm	median	bytes	× 66 175
A dependencies = nothing — today	1.00 µs	784 B	0.07 s / 0.05 GB
B dependencies = true	512 µs	541 664 B	33.8 s / 35.8 GB
C restrict(graph, [d])	193 µs	424 304 B	12.7 s / 28.1 GB

C's cost is the O(nsourcechunks) transpose G3 warned about, on the exact shape it warned about.

Gates

benchmark/chunk_graph_gates.jl before and after: the relation is identical on every relation field across all 26 rows, including the production pair's 326 064 / 326 386 edges and the 72 / 394 crossing. Both runs print verdict: PASS on 9 oracle-checked case(s); 4 case(s) unchecked. Production case timing +0.6 %.

suite	before (f9f268a)	after
lib/GlobalRegridding/test	3 828 / 1 broken / 0 fail	3 891 / 1 / 0 (+62 new gate tests, +1 tag assertion)
test/systems/crosssystem/regrid.jl	202 / 0	202 / 0
test/scripts/copdem_policy.jl	87 / 0	87 / 0
test/scripts/copdem_source_mode.jl	7 / 0	7 / 0
regrid_acceptance.jl	not baselined	22 / 0
CopernicusDEM/runtests.jl	not baselined	16 258 / 3 broken / 0 fail

🤖 Generated with Claude Code

https://claude.ai/code/session_019DuGKTmvs5B4EynwZddKMg