Inline token substitution — the templating model shared with phoenix_kit_og, ported for byte-compatibility so stored templates migrate without rewriting bindings.

Two bracket styles, both \w+ names, both resolved from a single values map:

• {{slot}} — a template-local slot, wired to a concrete value per render (the post title, hero src, …). Listed by slots/1 for a wiring UI, with a :text / :image type inferred from where it appears.
• [[global]] — a global that resolves from ambient context (site host, page URL, locale). Same substitution pass, different bracket; not listed as a slot.

Callers merge globals + wired slot values into one map (see OpenFresco.render_svg/3's :globals option).

The substitution contract (one path, both surfaces)

The editor stage and the PNG rasterizer resolve values through this exact module — there is no second substitution path — so what the author sees on the stage is what renders. The contract is:

• Bracket styles — {{slot}} (per-render wiring) and [[global]] (ambient context). Both name-match \w+.
• Undefined tokens pass through literally. An unwired {{Title}} renders as the visible text {{Title}} — og's "needs wiring" signal — never as an error or empty string. This is deliberate: a missing wiring should be obvious in the card, not silent.
• Escaping is the renderer's job, applied by default. Substitution returns plain text; OpenFresco.Svg XML-escapes every substituted value at the emission site. There is no "raw" opt-out — a template cannot inject markup through a slot value (see OpenFresco.Conformance). Hosts that need markup compose it into the scene as elements, not as substituted strings.
• Types — non-binary values (nil, numbers, a whole-value %{placeholder: k}) are coerced (nil → "", others via to_string/1); the placeholder form scans as its {{k}} token.

Deterministic: apply/2 is a pure function of (text, values).