S6 — unfao/wire/source_selection.py: contract-mode Hop-A inbound (manifest selection, await-all-targets)

[Polichinel]

Part of epic #105. Depends on S1.

Problem

The manager's inbound is legacy-only (LEGACY_FORECAST_FILTERS at unfao.py:121). The contract inbound — resolve the newest manifested run by contract type, wait for ALL configured targets (§4.2a), verify + assemble via track_a_source — does not exist. And track_a_source.frames_for_target discards headers, which the sink needs (provenance pass-through, §10.2 determinism).

Work

• Extend unfao/track_a_source.py: frames_for_target returns (frame, headers) — smallest surface, one existing reader to update.
• views_postprocessing/unfao/wire/source_selection.py: store passed as a port (any object with the get_latest_file_id/get_file_metadata/download surface — DIP, fake-able); selection filters pinned from pipeline-core's shipped publisher constants (type="sampled_forecast_manifest" etc., golden-string tested; re-verify their values at build); newest run wins; refuses loud when any configured product.TARGETS manifest is absent (await-all-targets); identity verified vs the launch declaration (reuse delivery/identity.assert_forecast_identity).

Acceptance criteria

• Dict-backed fake store serving the fixture Hop-A manifest + .tap.zip: returns per-target (frame, headers); assembled frame equals the existing test_track_a_source result.
• Missing configured target → loud refusal naming the target.
• No real store/network anywhere in tests.

Tests: tests/test_wire_source_selection.py (+ test_track_a_source.py update). Oracle: fixture Hop-A artifacts via fake store.

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