feat(scanner): GS1 prefix to country hint utility function (#928)

[ericsocrat]

Summary

Adds gs1_country_hint(p_ean text) — an IMMUTABLE SQL function that extracts the GS1 country-of-registration hint from an EAN-13 barcode prefix. This is a building block for issue #929 (admin mismatch detection).

Closes #928

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Changes

Migration (20260321000300_gs1_country_hint.sql)

• gs1_country_hint(p_ean text) → jsonb — IMMUTABLE STRICT, LANGUAGE sql
• Covers GS1 prefixes: PL (590), DE (400–440), FR (300–379), GB (50), IE (539), IT (800–839), ES (840–849)
• Store-internal detection: 020–029 and 200–299 ranges
• UNKNOWN fallback with prefix field for debugging
• NULL return for NULL/short input (STRICT)

Response shape

{"code": "PL", "name": "Poland", "confidence": "high"}
{"code": "STORE", "name": "Store-internal", "confidence": "low"}
{"code": "UNKNOWN", "name": "Unknown origin", "confidence": "none", "prefix": "999"}

Tests

• 12 pgTAP tests in scanner_functions.test.sql (plan 80 → 92)
  • PL, DE (×2 for range), FR, GB, IE, IT, ES prefixes
  • Store-internal (020 + 200 ranges)
  • Unknown prefix with prefix field assertion
• 1 schema contract in schema_contracts.test.sql (plan 302 → 303)

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Verification

3 files changed, +165 / -2 lines

• supabase/migrations/20260321000300_gs1_country_hint.sql — new migration
• supabase/tests/scanner_functions.test.sql — 12 new pgTAP tests
• supabase/tests/schema_contracts.test.sql — 1 new contract test

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Checklist

• Migration is idempotent (CREATE OR REPLACE)
• pgTAP tests cover all GS1 prefixes + edge cases
• Schema contract updated
• No API contract changes (internal utility only)
• No frontend changes required

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Project	Deployment	Actions	Updated (UTC)
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[Copilot]

Pull request overview

Adds a small Postgres utility (public.gs1_country_hint(p_ean text) -> jsonb) to derive a GS1 “country of registration” hint from an EAN prefix, intended as a building block for upcoming admin mismatch detection.

Changes:

• Introduces public.gs1_country_hint(p_ean text) as an IMMUTABLE STRICT SQL function returning a JSONB hint object (or NULL for short input).
• Extends pgTAP coverage in scanner_functions.test.sql and updates schema contract checks to assert the function exists.
• Updates pgTAP test plan counts to reflect the added assertions.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
supabase/migrations/20260321000300_gs1_country_hint.sql	Adds the gs1_country_hint SQL function and its comment.
supabase/tests/scanner_functions.test.sql	Adds pgTAP assertions for known GS1 prefixes and unknown/store-internal handling.
supabase/tests/schema_contracts.test.sql	Adds a schema contract assertion for the new function and bumps the plan.