Claims the Basic HTTP documents in the corpus

[johnnyt]

The corpus half of ADR-0075, on main now that the processor (#353) has merged (decision 7, and row g of decision 8): the W3C documents that need the Basic HTTP Event I/O Processor leave the exclusions and enter the corpus, and eleven of them are claimed.

What changes

• tools/corpus/scxml_w3/exclusions.exs drops its twelve :needs_basichttp entries and the reason line; mix statifier.corpus re-emits conformance/exclusions.json without them. The five needs_invoke_src entries (test216, test226, test239, test242, test276) are unchanged.
• conformance/schema/case.json gains host.event_io_processors: a non-empty, unique array whose item set is closed, its one member the Basic HTTP processor URI. The W3C branch's ban on host is lifted for that key only: a w3c case's host must carry event_io_processors and nothing else; scion cases still carry no host (ADR-0075 decision 7).
• Mix.Statifier.Corpus.Upstream declares the key for a W3C document that names the processor URI as a <send>'s type (HostCase.event_io_processors/1). Exactly the twelve documents do.
• Mix.Statifier.Corpus.HostCase.with_event_io_processors/2 starts the parent's loopback front (Mix.Statifier.BasicHTTPFront), registers Statifier.Send.BasicHTTP under the URI and basichttp with the front's base URL, and stops the front when the case ends; HostCase.run/2 uses it beside the recording send_types.
• The W3C generator emits, for such a case, test_scxml/5 inside HostCase.with_event_io_processors/2; every other generated module is byte-identical.
• conf:basicHTTPAccessURITarget emits targetexpr="_ioprocessors['basichttp']['location']", the IRP's spelling.
• docs/basichttp.md: what the processor is, registration, the location, the front a host writes around decode/1 and the status rule, the scxml-send-key header and at-least-once delivery (ADR-0075 Amendment of 2026-09-30), the mapping both ways, what is not supported (ADR-0075 decision 9's residue rows), and a req transport recipe as text. In mix.exs's extras and package files; linked from docs/extending.md.
• changelog.d/st-8kn8.md under Added.

The counts, beside their enumerations

• Claimed and ratcheted, eleven: test509, test510, test518, test519, test520, test522, test531, test532, test534, test567, test577. test/passing_tests.json grew by exactly these eleven paths (under test/scxml_tests/optional/basic_http_event_processor/), added by mix test.baseline add, which ran each before writing; conformance/registry.json grew by the same eleven case_ids. The w3c-optional claim goes from 2 cases (test193, test278) to 13 (those two plus the eleven).
• In the corpus and unclaimed, one: test201, out of both the ratchet and the registry. Its reason, from ADR-0075 decision 7, is recorded in conformance/RATCHET.md ("The host object"), docs/basichttp.md and tools/corpus/README.md: it expects an event delivered from outside the session ahead of a send the same step appends to the session's own external queue. Its generated module runs and fails, as test330 and test552 do today.
• Emitted W3C modules: 156 + 12 = 168 (154 mandatory, 2 + 12 = 14 optional); the README counts test pins the new figures in tools/corpus/README.md.

Provenance

• Restacked: this branch was first cut from Adds the Basic HTTP Event I/O Processor #353 before it merged. Adds the Basic HTTP Event I/O Processor #353 merged by rebase, so this branch now carries only its own commits, rebased onto main after the processor landed. The rebase was clean.
• Docs addition after the restack: docs/basichttp.md now covers what Adds the Basic HTTP Event I/O Processor #353 gained after this branch was cut. Every POST carries the send dedup key in an scxml-send-key header, and delivery is at-least-once. A front dedupes on the header value and answers a malformed one 400. The default adapter answers {:error, {:not_loadable, module, reason}} when :ssl or :public_key cannot be loaded. Checked against main at 3ffcf9d; cites ADR-0075 and its Amendment.
• Decisions: the host declaration in the case schema, ruled by the operator, 2026-09-29; the key's name, the per-key lift and test201 unclaimed are ADR-0075's.
• Beyond the brief's file map, forced by the change: conformance/RATCHET.md's host section said every W3C case omits host, so it now describes the new key (the contract a sibling port reads); README.md's and docs/testing.md's emitted counts; docs/extending.md now names the {module, opts} registration value and the optional ioprocessors_entry/2 the parent added, beside the link; Mix.Statifier.Corpus.Runner.start_runtime/0 puts :inets, :ssl and :public_key on the code path with Mix.ensure_application!/1, because mix statifier.corpus runs in the dev environment, where Mix pruning leaves :public_key off and a delivery through :httpc cannot be made without it; the generated modules alias HostCase (Credo's alias rule).
• Stale sentences ADR-0075 lists for this change, updated: the :needs_basichttp reason line in tools/corpus/scxml_w3/exclusions.exs; the "out of scope" comment in conf_predicator.xsl; tools/corpus/README.md's exclusions bullet; docs/testing.md's list of excluded trees.

Checks

• Full mix quality green on the restacked head, quoted whole in a comment below; mix quality --profile merge green (the ADR judge skipped: no file in the diff is in a judged scope).
• New tests carry sabotage notes; each mutation was run and turned its test red: HostCase registering nothing, dropping the short form, not stopping the front, the empty clause answering a non-empty map; Upstream not declaring the host; the schema's W3C additionalProperties and item enum removed; and without the ensure_application! call, mix statifier.corpus --check names the eleven ratcheted cases as disagreeing. These checks ran before the restack.
• CI: ci.yml on this pull request (base main). An earlier workflow_dispatch run on the stacked head is linked in a comment below.

[johnnyt]

CI (workflow_dispatch on this branch, since the base is not main): run 36723868371 at a9e3d35, conclusion success.
https://github.com/riddler/statifier-ex/actions/runs/36723868371

[johnnyt]

Full mix quality, quoted whole, run on the tree committed as cf0d389 (this branch rebased onto main at 3ffcf9d, plus the guide addition):

Running quality checks...

✓ Format: No changes needed (381ms)
✓ Compile: dev + test compiled (warnings as errors) (438ms)

Running analysis stages in parallel...

○ Gettext: skipped (:gettext not installed)
○ ADR judge: skipped (disabled in .quality.exs)
✓ Doc links: 38 links checked (89ms)
✓ Dependencies: No unused dependencies (899ms)
✓ Gate guard: No unjustified gate changes (1.1s)
✓ ADR guard: No likely ADR violations (1.4s)
✓ Sobelow: No findings (2.0s)
✓ Doctor: Passed (2.3s)
✓ Docs: No warnings (6.0s)
✓ Conformance corpus: Passed (7.3s)
✓ Credo: No issues (9.3s)
✓ Dialyzer: No warnings (12.3s)
✓ Regression ratchet: Passed (16.2s)
✓ Tests: 3,142 of 3,142 passed, 96.3% coverage (20.7s)

✓ All quality checks passed!