GFQL type system follow-on B: schema inference API + typed topology extraction

[lmeyerov]

Summary

Follow-on child slice for #1046: add a first-class schema inference API that derives typed schema + topology constraints from bound graph data.

Parent

• Umbrella: [FEA] GFQL native type system: schemas, inference, validation, and Arrow representation #1046
• Depends on: GFQL type system follow-on A: public declarative schema model + stable exports #1337 (public declarative schema model)

Goal

Provide infer_schema() (or equivalent stable API) that returns public schema objects inferred from node/edge dataframes, with typed-topology extraction suitable for compile-time validation.

In scope

• Public schema inference entrypoint
• Property type + nullability inference
• Typed topology extraction and representation
• User override/refinement flow for inferred schema
• Interop with schema declaration/binding path

Out of scope

• Full public Arrow/plottable schema boundary APIs

Acceptance

1. Inference API returns stable public schema objects.
2. Inference covers representative pandas and cuDF cases (where available).
3. Typed topology inference is deterministic and test-covered.
4. Inferred schema round-trips through the same binding path used by declared schema.
5. CHANGELOG/docs include explicit inference behavior and caveats.

Related

• [FEA] GFQL native type system: schemas, inference, validation, and Arrow representation #1046
• GFQL type system follow-on A: public declarative schema model + stable exports #1337
• Schema: Typed topology #483 (typed topology)
• Meta: GFQL compiler/planner post-M4 execution DAG (active wave) #1259

[lmeyerov]

Scoping alignment note: lane D #1345 tracks cross-lane API contract alignment in parallel.\n\nThis lane B issue remains independently executable and non-blocked by D; please include compatibility notes needed for D drift checks.

[lmeyerov]

Coordinator schedule note: #1464 is now the follow-up tutorial lane and should start after this inference issue lands.

The intended handoff from #1338 to #1464 is: tutorial demonstrates loading graph data, running infer_schema(), refining/overriding the inferred schema, binding it to a graph, and validating Cypher with one passing case plus one structured failure. This keeps the community-facing documentation inference-first instead of hand-authored-schema-first.