Head and history interfaces, and interceptors over every host import - #25
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Two more platform interfaces, both unconditional imports of `world app`: - `head`: `set-title` and `create-element`, the back end of dioxus's `document::Title`/`Meta`/`Link`/`Style`/`Script`. Until now those routed through `eval`, which apps do not have; now they are plain DOM writes the host performs. The default host refuses `script` unless the mount granted eval. - `history`: dioxus-history's `History` trait over abstract routes, with host-initiated moves delivered as a `stream<string>` from `changes()`. The host chooses the encoding (`MountOptions.history`: `"memory"` by default, `"fragment"` for a host that does not own the path); the guest never sees it, so dioxus-router works unchanged. And one mechanism over all of them: `MountOptions.intercept` lets the embedder wrap any operation of any host-implemented import table with `(next, ...args) => result` — observe, rewrite arguments, refuse, or replace. Policy stays out of the WIT, which remains one fixed protocol per capability. Rules in host/src/intercept.ts: typed per operation (a sync import cannot be given a Promise-returning interceptor), one denial spelling per return type (`false`, `undefined`, or `eval`'s new `denied` case, which the guest maps to `EvalError::Unsupported`), the dispatch-gate bracket sits outside the interceptor, throwing is a host bug, and interceptors never grant a capability the mount did not. The eval-probe fixture becomes platform-probe and also exercises head elements and a two-route router, including a host-driven navigation.
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September 5, 2026 13:00
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Follow-up to #23/#24, covering the remaining platform gaps against dioxus-web and the customization hook polyvisor needs.
New WIT (
wit/world.wit), both unconditional imports:head:set-title,create-element(tag, attrs, contents) -> bool. Retires the "head elements need eval" gap. Default host refusesscriptunlessevalis granted.history: dioxus-history's trait over abstract routes;changes() -> stream<string>carries host-initiated moves (back button, visor navigation). Encoding is host-side:MountOptions.history: "memory" | "fragment". Hydration note in the doc: a hydrating host must answer the prerendered route first.eval.error.denied→ guest maps toEvalError::Unsupported(the graceful path apps already handle).Interceptors (
host/src/intercept.ts, normative header):MountOptions.intercept.{dom,eval,head,history}— per-operation(next, ...args) => result. Typed against each fragment's import table; denial has one spelling per return type; gate bracket is outside the interceptor (fragments wrap their unbracketed impls then bracket); throwing = host bug (trap);intercept.evalwithouteval: truethrows at mount.Example polyvisor policy:
Guest:
WitDocumentgainsset_title/create_head_element(queue_effect'd as dioxus-web does;dioxus-documentis now a plain dependency,evalstill feature-gated); newsrc/history.rsWitHistorywithupdaterreadingchanges. Both provided as root context.Tests: unit tests for
wrap, head, history (memory provider,changes, interceptor refusal);platform_component_test.tsdrives the real fixture through eval (incl. denial), head (incl. script refused via interceptor), and router (click + host-drivenforward()). 142 deno tests; fulljust check/fixtures/example/ssg-example/serve-test/testpass.Not covered here (documented gaps remaining): clipboard/file payloads, suspense in hydration.
Automerge armed (merge commit).