tax_estimate

        Terms §7 contract: "Preview the tax for any order with the
        ``tax_estimate`` tool before placing it.  We display the full
        fee + tax breakdown before charging.  No hidden fees."

        This tool fulfills that contract by returning the same line
        items the order will commit to at charge time.  Per Terms §7
        tax is computed on the orchestration fee ONLY — never on
        the manufacturer's quoted total.  The manufacturer is
        responsible for any taxes on their own charges.

        Two calling shapes are supported:

        1. **Canonical preview** (recommended): pass
           ``manufacturer_quote_usd`` and the tool returns the
           full breakdown — ``manufacturer_quote``,
           ``orchestration_fee``, ``tax_on_fee``, ``total`` — so
           the agent can show the user the exact line items that
           match the eventual charge.  This is the shape Terms §7
           commits to.
        2. **Tax-only legacy** (compatibility): pass ``fee_amount``
           with no ``manufacturer_quote_usd`` and the tool returns
           the older ``{tax: {...}}`` shape, useful for callers
           that already know the fee and only want the tax line.

        Args:
            fee_amount: Legacy — the platform fee amount (from the
                quote's ``kiln_fee``).  Used only when
                ``manufacturer_quote_usd`` is omitted.
            jurisdiction: Where the buyer is located (e.g.
                ``"US-CA"``, ``"DE"``, ``"AU"``).  Use
                ``tax_jurisdictions`` to see all supported codes.
                When empty in canonical-preview mode, no tax is
                applied (preview shows manuf + fee only).
            business_tax_id: If the buyer is a business, their tax
                ID (e.g. EU VAT number).  In the EU, UK, Australia,
                and Japan, businesses are exempt — the tax line
                shows $0.00 with a note that reverse charge
                applies.
            manufacturer_quote_usd: Provider's quoted price (e.g.
                from ``fulfillment_quote``).  When non-zero,
                triggers canonical-preview mode.
            currency: Currency of the manufacturer quote (default
                USD).  Tax rates are applied at the standard
                jurisdiction rate regardless.
            user_email: Buyer's email — affects the free-tier
                waiver (first 3 fulfillment orders/month per user
                are fee-free).  Available in canonical mode only.

        Returns:
            Canonical mode (``manufacturer_quote_usd > 0``):
                ``{success, manufacturer_quote, orchestration_fee,
                tax_on_fee, total, currency, fee_waived,
                fee_waiver_reason, tax_jurisdiction,
                tax_rate_percent, tax_reverse_charge, note}``.
            Legacy mode (``manufacturer_quote_usd == 0``):
                ``{success, tax: {...}}``.

        Read-only — charges no card, contacts no provider.