[EthanThatOneKid]

What

The @wazoo/wiki/theme entrypoint now exports a whole-site driver for a custom theme, buildThemedSite, so a theme no longer reimplements the page loop. This is the engine half of #409; the wiki-templates wikipedia theme consumes it in the follow-on change (blocked on publishing this).

Before this, docs/build.ts (791 lines) and templates/wikipedia/build.ts (797 lines) differed by ~113 lines — the page loop, the token table, the infobox/categories/backlinks/TOC builders, and the metadata-panel emission were duplicated.

What moved

• src/wiki/site/theme_build.ts (new) owns page walking, the page shell (TOC, infobox, backlinks, categories, metadata panels), %wiki.*% substitution, output writing, and asset copying.
• The theme supplies only what actually differs between themes: layout files, assets, title_suffix, tokens (extra or overriding %wiki.*% values), and metadata (views, selected_view, note, highlight).
• docs/build.ts drops from 791 to 93 lines and is now policy only: the two layouts, the - Wiki title suffix, and the two tokens that need a GitHub remote (edit link, redirect URL).
• escapeHtml, safeJson, and substitute are exported so a theme can compose its own token values; the shell slot list is documented.

Decisions recorded once, in the shared contract

• The xml metadata view is excluded by default. The reason (RDF/XML output is deferred while input is supported) is stated in the module doc, so themes stop rediscovering it. metadata.views re-enables it.
• metadata.highlight returns HTML (escape the text yourself when the grammar highlights nothing); the default escapes the whole body. This is what lets the docs theme escape and the wikipedia theme highlight with Prism through one code path.
• A token neither the engine nor the theme fills is left verbatim, so residue is checkable. The engine's built-in renderLayout still fills only three slots; buildThemedSite fills the full shell of nineteen. Both are documented as such.

Verification

Output-neutral by construction, and proven:

• Built the docs site on pristine main into a baseline tree, then again after the refactor: 114 files, every SHA256 identical (Built 111 pages).
• After the docs edits in this PR, re-built and diffed against the refactor-neutral tree: the only changed files are the two reference pages this PR edits. No structural drift.
• deno check src/wiki tests docs/build.ts → exit 0
• deno run -A src/wiki/cli.ts -c docs/wiki.yml fmt --check | lint --strict | check --strict | render --check → all exit 0
• deno task fmt:check / deno task lint / deno task check → exit 0
• deno task test → 569 passed, 1 ignored, 5 failed. The 5 are tests/verify_cli_test.ts (retired-Python-CLI-on-PATH and cutover-version cases); they fail identically on pristine main in this environment. The count is 569 rather than the previous 568 because this PR adds one test.
• New test buildThemedSite owns the flow while the theme owns the vocabulary covers a minimal theme: custom layout, title_suffix, a tokens table, a highlight override, a redirect_layout, index filtering, asset copying, the xml-view default, and the verbatim-unfilled-token rule.

What I could not verify

• The wiki-templates wikipedia theme's build against this surface. It pins the published package, so it cannot consume buildThemedSite until this is released; that refactor and its output comparison are the follow-on change (T5b), per AGENTS.md ("Bump pinned versions only after publishing").