Adds a library hold at its own BasicHTTP location

[johnnyt]

The reference host now shows statifier_router's durable BasicHTTP front, in the library world only.

What it does

• StatifierExamples.HoldDesk: a router configuration of its own that sets :basichttp (base URL: the endpoint's URL plus /basichttp). Each hold execution it creates gets a location. StatifierExamples.RoutedWorkflow's parcel configuration sets no :basichttp, and a test asserts that.
• The chart (priv/library/hold_desk.scxml): a patron's hold at a branch desk. On hold.requested it sends hold.placed with <send type="basichttp"> to the desk the request names, passing reply_to read from _ioprocessors['basichttp']['location']. It finishes in shelved on copy.shelved, or in desk_unreached on error.communication.
• The outbound send: planned with StatifierRouter.BasicHTTP.deliver/3 and performed with perform/2 in the host's own executor (HoldDesk.execute/2). The router leaves outbound sends at the executor seam to the host. A delayed BasicHTTP send is refused.
• The front: StatifierExamplesWeb.BasicHTTPController.event/2, routed for every method at /basichttp/:token outside the browser pipeline. It builds the request map, calls StatifierRouter.BasicHTTP.Front.handle/3 and answers Front.response/1: 204, 404, 405 with allow: POST, or 400.
• The location table: priv/repo/migrations/20260930120001_add_statifier_router_locations.exs calls StatifierRouter.Migrations.up_locations/1 (down_locations/1 on rollback). It uses the same depot_id leading column as the app's first router migration.
• The bearer capability: a location is a bearer capability (ruled by the operator, 2026-09-30). The new guide docs/guides/basichttp-front.md, the HoldDesk moduledoc and the controller moduledoc all say so.
• Tests: test/statifier_examples_web/controllers/basic_http_controller_test.exs drives it end to end through the endpoint with Phoenix ConnTest on the app's SQLite. The outbound POST goes to a test transport (test/support/desk_transport.ex), which hands it back to the test. The test then POSTs copy.shelved at the reply_to location through the controller.

Dependencies

• {:statifier_router, "~> 0.9.2"}. 0.9.2 is the first release whose migrations (V03, fixed in 0.9.1) and Addresses.reap/3 (fixed in 0.9.2) both run on this app's SQLite database. 0.9.0 ships the front.
• {:statifier, "~> 2.10"}, which router 0.9.2 requires. It ships Statifier.Send.BasicHTTP.
• mix.lock moves three entries: statifier 2.9.0 to 2.10.0, statifier_router 0.6.0 to 0.9.2, and statifier_persistence 0.21.0 to 0.24.0, which came in with the router update. The persistence requirement stays at ~> 0.20, and none of 0.22.0 to 0.24.0 adds a migration.
• No version bump of this app.

Provenance

These changes are forced by the bead but were not in its file map:

• Raw-body reader on the endpoint. Plug.Parsers consumes a form body before any action runs, and the front needs the body as it arrived. The parsers now take body_reader: {StatifierExamplesWeb.RawBody, :read_body, []}, which keeps the raw body only for /basichttp paths. Every other path reads as before.
• Guide version tables. docs/guides/first-workflow.md, docs/guides/first-workflow-routed.md and docs/guides/migrating-waiting-executions.md state what mix.lock resolves. Their pin tables and move notes now name the new versions: version facts only, no new example. Three tests that pin versions in the recipes' first output line now match the new lines (first workflow, routed workflow, migrate waiting), and test/statifier_examples/mix_deps_test.exs asserts the new requirements and lock entries.
• persistence 0.21 to 0.24. See Dependencies.
• Review cure: the token stays out of the request log. The desk's POST path carries the location's token, and Phoenix logged it with the request line at :info. The endpoint's Plug.Telemetry now takes log: {StatifierExamplesWeb.Endpoint, :log_level, []}, which logs no request line under /basichttp; the route is log: false; and config :phoenix, :filter_parameters names token beside password. A test captures a POST at :debug and finds the token in no log line except Ecto's query lines. At :debug those print bound parameters, and the router binds the token, so the guide and the controller's moduledoc tell a host to keep :debug out of production.
• error.communication, not a failed route. An executor {:error, _} for a send does not fail the delivery: statifier_persistence enters error.communication into the execution in the same step. The chart takes that to desk_unreached, and a test covers it.

Gate

Full mix quality on the committed tree (head after the review cure). The same tree (git write-tree before and after the run) was committed with the repo gate lock and a machine slot held throughout:

✓ Format: No changes needed (371ms)
✓ Compile: dev + test compiled (warnings as errors) (1.6s)
○ Doctor: skipped (:doctor not installed)
○ Docs: skipped (opt-in; set docs: [enabled: :auto] in .quality.exs)
○ Doc links: skipped (opt-in; set doc_links: [enabled: :auto] in .quality.exs)
○ Sobelow: skipped (:sobelow not installed)
○ Gettext: skipped (no .po files outside the source locale)
✓ Dependencies: No unused dependencies (398ms)
✓ Credo: No issues (1.7s)
✓ Dialyzer: No warnings (4.7s)
✓ Tests: 655 of 655 passed, 84.8% coverage (49.8s)
✓ All quality checks passed!

Each sabotage noted above a new test was run on its own, restored from a copy (byte-equal by cmp) and recompiled. Each turned a named test red on an assertion, including Phoenix ConnTest's response/2 status check.