docs: surface pst!/get! HTTP auto-unwrap forms (#5bm)

[danieljohnmorris]

Summary

The ! auto-unwrap suffix has worked on get / pst / get-to / pst-to since the bang family was generalised, but skills/ilo/ilo-builtins-io.md only called it out under JSON. Several recent persona runs (basic-auth, webhook-sender) reached for the manual ?r{~v:v;^e:^e} shape on every HTTP call site, paying ~30 tokens per call that the bang form would have saved. Pure doc gap, not a runtime gap.

Fix: add a paragraph in the HTTP section showing all three forms (get, get!, get!!) with a one-line caveat on when to reach for which, plus a tiny runnable example so the engines harness pins the contract.

Manifesto framing: token-minimal language only works if the token-minimal idiom is the obvious one. Hiding pst! under the JSON heading made the longer shape feel default.

Repro before / after

Before, basic-auth persona wrote:

r=pst url body
?r{~v:v;^e:^e}

After, same shape collapses to:

v=pst! url body

inside any function that already returns R.

What's in the diff

• add http-bang example pinning get!/pst! propagation: examples/http-bang.ilo exercises get! / pst! / get-to! / pst-to! via the engines harness. Uses connection-refused on loopback for a stable Err, then matches on the Result tag so the assertion is OS-portable.
• surface HTTP bang forms in skills io doc: adds the three-form table + one-line caveat to the HTTP section of skills/ilo/ilo-builtins-io.md. Mirrors the wording style of the existing ! paragraph under JSON.

Test plan

• cargo test --release --features cranelift, full suite green
• cargo test --release --test examples_engines, http-bang.ilo passes
• cargo fmt --check
• cargo clippy --release --features cranelift -- -D warnings
• Manual: ilo examples/http-bang.ilo --vm probe-{get,pst,get-to,pst-to} all emit err propagated

Follow-ups

None. SPEC.md already documents get!; ai.txt lists the builtin signatures and inherits the ! rule from the language spec. This PR only closes the skills-doc gap.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

📢 Thoughts on this report? Let us know!