bdeshi
61ae5c9c14
A feature now learns which bundle is rendering: render.Bundle puts an Origin —
the bundle's directory plus the rooted fs.FS — on the parse context, and
render.OriginFrom reads it back. Available while parsing, not while rendering,
which decides where a feature does its filesystem work: goldmark hands the
context to a block parser and not to a node renderer, so gallery gathers its
filenames at parse time and carries them on the node.
Reads stay inside the site root because Origin passes the fs.FS rather than a
path to join (ADR-0031).
Fragment{Args, Items} lands with it (ADR-0037), so figure's template now reads
.Args.src. Authored arguments and engine-gathered items stay in separate fields:
a src argument beside a src the engine found would otherwise silently pick one.
A gallery is pictures beside the bundle, in filename order, skipping
subdirectories and anything a browser cannot show. Filename order is what makes
the sparse numeric-prefix convention work without numbers in URLs (ADR-0016).
New latent row: the reference theme's images carry no width/height and a
gallery's carry no alt, which is below the output floor conventions.md states.
Nothing can supply either yet — dimensions need the image read, and a filename is
not alt text. Queue 13 computes dimensions and brings structured items with it.
189 lines
11 KiB
Markdown
189 lines
11 KiB
Markdown
# Theme contract
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What the engine promises a theme, and the only thing this repository is bound to (ADR-0023). A theme's
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markup, layout and styling are not the engine's business; a theme's *inputs* are.
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**STATUS: partly live.** The fields under *Live today* exist and are gated; everything else is the shape
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the contract takes when the feature arrives. All of it is engine obligation, not theme instruction — a
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theme may ignore any of it.
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## Live today
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A bundle page receives:
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| Field | Contents |
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| `.Title` | may be empty; a template falls back to `.Key` rather than failing |
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| `.Lang` | the locale of this variant, always set |
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| `.Key` | the bundle's identity, without language or extension |
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| `.HTML` | the rendered body, already escaped |
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| `.Extra` | every frontmatter key the parser does not name (ADR-0002) |
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| `.Style` | the reference theme's stylesheet, inlined so a bare site root needs no asset route |
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| `.Canonical` | the permalink of the variant actually served — not the URL requested, which differs when the fallback chain supplied another language |
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| `.Alternates` | every language this key exists in, as `.Lang` and `.URL`, for `hreflang` |
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| `.Sequence` | the series this page sits in, absent when it sits in none (ADR-0033) |
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`.Sequence` carries the reading order and this page's place in it:
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| Field | Contents |
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| `.Sequence.Title`, `.Sequence.URL` | the series' title (may be empty) and its permalink |
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| `.Sequence.Members` | every entry in reading order, each as an `.Items` entry — *ascending*, unlike a dated listing |
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| `.Sequence.Index`, `.Sequence.Count` | this page's 1-based position and the total; `Index` is 0 when this page is the series landing itself |
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| `.Sequence.Prev`, `.Sequence.Next` | the neighbours, absent at the ends and on a landing page. `Prev` is the **earlier** entry — the opposite sense of a listing's `.PrevURL` |
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| `.Sequence.First`, `.Sequence.Last` | the ends of the series, present whenever it has members |
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A landing page therefore renders an archive from `.Members` and a chapter renders navigation from
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`.Prev`/`.Next`, both from one field. Membership and order are the engine's business
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(`content-model.md`); a theme never sorts.
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Two named templates: `base` is executed for every page; `main` is the block each kind of page defines and
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a theme redefines. There is one parsed set per kind — bundle and listing today — so two kinds may both
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define `main` without colliding (ADR-0019).
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A listing page receives `.Title`, `.Lang`, `.Canonical`, `.Style` as above, plus:
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| Field | Contents |
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|---|---|
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| `.Items` | entries on this page: `.Title`, `.Key`, `.URL`, `.Date` |
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| `.Page`, `.Pages` | 1-based position and total, `Pages` at least 1 |
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| `.PrevURL`, `.NextURL` | empty at the ends; *newer* is `prev`, because the order is newest first |
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| `.Groups` | set instead of `.Items` when entries are grouped — a tag listing groups by section, each `.Name` and `.Items` |
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## Chrome text and formatting
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Three functions, available in every template including a site root's own blocks. They exist so no template
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hardcodes English: the words the engine supplies are the engine's to localise (ADR-0034).
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| Call | Gives |
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| `{{t .Lang "newer"}}` | one phrase in that language. Extra arguments fill `%s` placeholders in order |
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| `{{num .Lang .Page}}` | an integer in that language's digits — `12`, `১২` |
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| `{{day .Lang .Date}}` | a date as that language reads it — `8 March 2026`, `৮ মার্চ ২০২৬`; empty for a zero date |
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Phrase keys today: `newer`, `older`, `empty`, `page-of` (two arguments), `position` (two arguments). An
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unknown language falls back to the default locale and an unknown key returns itself, so a missing
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translation can never blank a page or fail a render.
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Three rules a theme must keep: put the machine-readable form in the attribute and the localised form in the
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text — `<time datetime="{{.Date.Format "2006-01-02"}}">{{day .Lang .Date}}</time>`; never localise
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`.Title`, `.HTML` or anything else the author wrote; and never pass a URL, key or path segment through
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these functions. An address is not chrome (`content-model.md`).
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A site root cannot add or override a phrase yet. A theme needing its own words writes them in its own
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block; site-supplied strings wait for the settings cascade (`ideas/deferred-decisions.md`).
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## Shortcode fragments
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`templates/shortcodes.html` holds one named template per shortcode, and that is where a shortcode's markup
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lives — the engine parses the call and supplies its data, never any HTML (ADR-0036).
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Every fragment receives the same two fields (ADR-0037):
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| Field | Contents |
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| `.Args` | the call's `key="value"` pairs, exactly as the author wrote them |
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| `.Items` | a list the *engine* gathered, empty unless that shortcode gathers one |
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| Shortcode | Template | Receives |
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| `{{< figure src="…" alt="…" caption="…" >}}` | `figure` | `.Args.src`, `.Args.alt`, `.Args.caption` |
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| `{{< gallery >}}` | `gallery` | `.Items` — the picture filenames beside the bundle, in filename order |
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Authored and engine-supplied data are kept apart so a `src` argument can never be confused with a `src` the
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engine found. Arguments are escaped by `html/template` like any other data, in whichever context the
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template puts them — which is what keeps an author's text out of the markup. A call whose template is
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missing renders nothing and logs; it never fails the page.
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A gallery entry is a bare filename, relative to the bundle, so a template writes it straight into `src`. It
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carries no alt text or dimensions, because nothing in a filename supplies either.
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The set is overlaid the same way as the page kinds: a site's `templates/shortcodes.html` is parsed after
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the embedded one, so redefining `figure` replaces it and any fragment left alone is inherited. Argument
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names are contract, added but never renamed.
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## The stability rule
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Fields and names are **added, never renamed or removed**. Absence is always legal: a template reading a
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field that does not exist gets the zero value and must not crash, and the engine must not make a missing
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field fatal at request time (ADR-0002, invariant 1). This is the View-layer freeze from
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`architecture.md`, arriving as soon as a theme exists rather than at Arc 2.
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Breaking the contract is not a feature — it is a new contract version, and it needs an ADR.
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## What the engine provides
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| Provides | Detail |
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| the page object | known fields plus an `Extra` bag carrying unknown frontmatter (ADR-0002) |
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| the resolved cascade | settings after site → section → bundle resolution (`ideas/deferred-decisions.md`) |
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| queries the page needs | its sequence neighbours, its taxonomy terms, its section's members |
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| named template lookup | per-type sets; a theme redefines a named block and inherits the rest (ADR-0019) |
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| URLs | every path the engine emits, so a theme never constructs one by hand |
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| per-page assets | the `styles` / `scripts` frontmatter lists, resolved relative to the bundle |
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| chrome strings | looked up by key and language, never hardcoded English in a template — live, see above |
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| validity windows | a template that renders time-dependent output declares one |
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## Extras view
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For a request under a bundle's extras directory (`ideas/deferred-decisions.md`) the engine additionally provides:
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| Field | Contents |
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| `.Extras.Entries` | the tree: `Name`, `Path`, `URL`, `RawURL`, `Kind`, `Size`, `IsDir`, `ModTime` |
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| `.Extras.Selected` | nil on the bare listing; otherwise the chosen entry |
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| `.Extras.Selected.HTML` | rendered output for `markdown` and `text` kinds; empty otherwise |
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| `.Extras.Selected.RawURL` | always present — for `<img src>`, `<object data>`, or a download link |
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`.Bundle` is the parent, so a theme has its title, language and breadcrumb. Selecting an entry is an
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ordinary link and a full re-render, so a sidebar-plus-pane layout needs no JavaScript; swapping the pane
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client-side is a later enhancement over working markup, never a requirement.
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## What the engine does not provide
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Layout, class names, CSS, client-side behaviour, and any choice about how something *looks* — including
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how media is embedded, how a listing is arranged, and whether something appears in a sidebar. Those are
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theme decisions, and a request touching them is split: a contract extension here, a change there.
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The engine also does not provide a component library, a CSS build step, or a JavaScript runtime.
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`conventions.md` holds the output floor the engine itself meets — semantic HTML, zero-JS, every image
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carrying width, height and alt — and a theme is expected to stay inside it, but the engine does not
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enforce a theme's markup.
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## The reference theme
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The binary embeds a reference theme — templates plus one small stylesheet — so a bare site root renders
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(ADR-0026). It exists to make this document executable: it implements every field and block named here and
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nothing else, and a golden-file test through it catches contract regressions before a real theme does.
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It is not a design. Legibility only, no branding, no visual opinions, no JavaScript — `verify.sh` fails on
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a `<script` tag in it. If it starts accumulating taste, it has stopped being a reference.
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It demonstrates the contract; it is not the contract. Changing it does not change what a theme may rely on
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— which is why `verify.sh` also fails when it changes without this document changing, since in practice the
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two drift together.
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## Overriding it
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A site root's `templates/` is parsed **after** the embedded set, and the last definition of a name wins, so
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a theme redefines one named block and inherits the document (ADR-0019). Each set is built from named files
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and only those are overlaid — `base.html` plus that kind's block file (`page.html` or `list.html`), and
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`shortcodes.html` on its own. Overlaying every site template into every set would let a listing's `main`
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leak into bundle pages, which is the collision per-kind sets exist to prevent.
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`templates/theme.css` in the site root replaces the reference stylesheet entirely; there is no merging.
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`static/` in the site root is served verbatim under `/static/`. Directory paths answer 404 rather than
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listing their contents.
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## Splitting a request
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When a feature spans engine and theme, this repo delivers:
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1. the contract extension — new fields, new named blocks, new queries, new URLs;
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2. a note stating what a theme must do to use it, precise enough to act on without this conversation;
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3. embedded defaults updated far enough to prove the extension works.
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It does not deliver the theme. Claiming otherwise is the same error as claiming to have migrated content
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in a site root this repo cannot see.
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