feat(docs): let a renamed site redirect its retired hostnames

[rubenvdlinde]

The gap

docs-hosts makes one worker answer on several hostnames — and it serves the same bytes on each. That is exactly right on the day of a rename: the old address must not break. It is wrong from then on.

Measured across the fleet on 2026-08-29: all 13 renamed apps answer 200 on both hostnames, and none of them redirects.

openconnector.conduction.nl  200  <no redirect — serves content directly>
docudesk.conduction.nl       200  <no redirect — serves content directly>
openbuild.conduction.nl      200  <no redirect — serves content directly>
scholiq.conduction.nl        200  <no redirect — serves content directly>
planix.conduction.nl         200  <no redirect — serves content directly>

So every renamed app has two live copies of every documentation page, and the retired name stays as discoverable as the current one.

The change

A worker with only [assets] has no code to read the Host header, so it cannot express this. The new optional canonical-host input adds a small script in front of the asset binding:

• hostname ≠ canonical → 301 to the same path and query on the canonical host
• otherwise → env.ASSETS.fetch(request), untouched

Delegating rather than reimplementing is deliberate: the asset binding keeps its own html_handling and 404 behaviour, so an opted-in site serves exactly what it served before on its canonical host.

301, not 302 — the hostname is retired, not moved for the afternoon, and only a permanent redirect makes search engines and caches forget it.

Opt-in, so a rollout cannot regress anyone

With canonical-host unset the generated wrangler.toml is byte-for-byte what it was and no script is emitted at all.

Verification — by running the generator, not reading it

The step's script was extracted from the YAML and executed both ways:

	without canonical-host	with it
wrangler.toml	identical to today	gains main + binding = "ASSETS"
worker script	not emitted	emitted, passes node --check

And the handler was exercised against real Request objects:

ok   openbuild.conduction.nl/docs/intro      -> 301 buildiq.conduction.nl/docs/intro
ok   openbuild.conduction.nl/docs/a/b?x=1&y=2 -> 301 buildiq.conduction.nl/docs/a/b?x=1&y=2
ok   openbuild.conduction.nl/                -> 301 buildiq.conduction.nl/
ok   buildiq.conduction.nl/docs/intro        -> 200 (serves asset)
ok   buildiq.conduction.nl/                  -> 200 (serves asset)

Deep paths and query strings survive; the canonical host is unaffected.

Rollout

Nothing changes until an app sets the input. Next step is one app (buildiq, already publishing, with openbuild as its retired host), verified live, before the remaining twelve.