Singapore: IRAS document titles and GST Reg No. labels

[methodofaction]

What

Regime-specific rendering for Singaporean invoices, in a new components/regimes/sg package following the existing co/ar pattern:

Document title — IRAS requires the words "tax invoice" in a prominent place on a GST tax invoice, and conversely a supplier that must not issue one must not use the heading. For SG standard invoices the title is now derived from supplier GST status and tags instead of the static "Invoice":

Condition	Title
Supplier has no GST number (tax_id.code empty)	Invoice
self-billed tag (recipient issues the tax invoice)	Invoice
simplified tag	Simplified Tax Invoice
reverse-charge tag	Customer Accounting Tax Invoice
Otherwise	Tax Invoice

Credit notes and all other document types fall through to the default titles. The headings are intentionally left untranslated in other locales since the English wording is what IRAS mandates.

Supplier identifiers — SG tax IDs are labelled GST Reg No. instead of the generic TIN. A UEN identity that duplicates the GST registration number is no longer rendered (IRAS reuses the UEN as the GST number for most entities), collapsing the previous three-line output to one. When the values genuinely differ — GST group/divisional registrations, sole proprietorships, overseas vendors — the UEN renders separately as Company Reg No.. The comparison is hyphen-insensitive; an explicit identity label still takes precedence.

Why

A Singaporean customer document (PPL000003) rendered a heading of just "Invoice" — not a valid tax invoice under IRAS rules, exposing GST-registered buyers relying on it for input tax claims — plus the same identifier repeated under three labels (TIN, Company Reg. no, GST Reg No).

Notes for review

• No GOBL change: regimes/sg validation was verified against the IRAS-published format table and is correct as-is.
• The Gross Margin Scheme case (also a plain-"Invoice" case per IRAS) has no GOBL representation today, so it cannot be derived; one-line addition to titleKey if that ever lands.
• The HTML <title> tag comes from bill.DocumentTitle, which no regime hooks into (same pre-existing desync as AR/CO/PT/GR/IT), so the tab title still shows the default wording; the printed document is correct.
• Four new example fixtures + goldens cover each case: simplified (mirrors the reference document), standard, divergent UEN/GST, and non-registered supplier.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds Singapore (IRAS) regime-specific rendering so SG invoices show the correct legally-significant document headings and more accurate GST/UEN identifier labels, following the existing regime-component pattern.

Changes:

• Introduces a new components/regimes/sg package to derive IRAS-compliant invoice titles (Tax Invoice / Simplified Tax Invoice / Customer Accounting Tax Invoice).
• Updates party identifier rendering to label SG tax IDs as GST Reg No. and suppress duplicate UEN output when it matches the GST registration number.
• Adds SG example fixtures and corresponding rendered HTML outputs, and links them from the examples index.

Reviewed changes

Copilot reviewed 10 out of 17 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
locales/en/app.yml	Adds English strings for SG regime-specific invoice titles.
examples/sg-invoice.json	New SG standard invoice example fixture.
examples/sg-invoice-simplified.json	New SG simplified tax invoice example fixture.
examples/sg-invoice-not-registered.json	New SG non-GST-registered supplier example fixture.
examples/sg-invoice-gst-group.json	New SG example where UEN differs from GST reg no.
examples/out/sg-invoice.html	Golden HTML output for SG standard invoice title/labels.
examples/out/sg-invoice-simplified.html	Golden HTML output for SG simplified tax invoice title/labels.
examples/out/sg-invoice-not-registered.html	Golden HTML output for non-registered supplier (plain invoice + company reg no.).
examples/out/sg-invoice-gst-group.html	Golden HTML output for divergent UEN/GST (renders both lines).
examples/index.html	Adds preview cards for the new SG examples.
components/regimes/sg/sg.templ	Adds SG regime title-type templ component hook.
components/regimes/sg/sg.go	Implements IRAS title selection and SG identity hide/label logic.
components/regimes/sg/sg_templ.go	Generated templ output for SG components.
components/org/party.templ	Wires SG identity hide/label behavior into party rendering; adds SG tax label.
components/org/party_templ.go	Generated templ output reflecting updated party rendering logic.
components/bill/invoice.templ	Adds SG title hook into invoice title coalescing chain.
components/bill/invoice_templ.go	Generated templ output reflecting invoice title hook update.

Files not reviewed (3)

• components/bill/invoice_templ.go: Generated file
• components/org/party_templ.go: Generated file
• components/regimes/sg/sg_templ.go: Generated file

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[mrdanwa]

LGTM!