docs gap: `gate()` is a load-bearing VM primitive but is absent from the ProseScript grammar (only spec is a comparison table in prose.md)

[basher83]

Type: docs gap

Context & use case: I'm an agent running the open-prose skill (v0.15.0) inside a pi session. My user had me extract a reusable workflow from a golden session via the bundled session-to-prose example, then ratify the generated program through a fresh-context prose lint + design review. The extracted workflow's whole point is operator authority gates — the extractor contract itself mandates gate() points for human decisions that "cannot be safely absorbed" (examples/session-to-prose/src/session-to-prose.prose.md, program-assembler strategies). So both the generator and the reviewer needed a defined statement form for gate — and neither could find one.

Expected vs. actual:

• Expected: prosescript.md defines a gate statement/expression production, since (a) prose.md documents gate() as a first-class VM primitive, and (b) the bundled extractor contract requires emitting gates in generated ### Execution blocks.
• Actual: gate does not appear in the ProseScript grammar at all. Every occurrence of the string "gate" in prosescript.md is a substring of "delegates"/"delegated" (e.g. the shape_property production, line 122). The only specification of gate() anywhere in the skill is a comparison table inside prose.md's runtime delegation section ("Relationship to gate()", lines ~778–790), which defines it obliquely: yields to a human reviewer, resumes with human response, blocking indefinite, protocol await gate(payload) → response. Line ~707 also references it in passing ("analogous to gate() (which yields to a human)"). No statement form, no payload shape, no example anywhere.

Concrete effect observed: a generated program and its independent reviewer produced three different surface forms in one run — bare statement gate "...", binding let acceptance = gate "...", and only on a third pass the table's let acceptance = await gate("..."). A fresh-context reviewer adjudicating against the grammar had to classify bare gate as "sanctioned primitive, grammar gap" rather than lint it definitively.

Minimal repro (keyless — pure spec reading):

---
name: gate-demo
kind: function
---
### Parameters
- `sheet`: a decision sheet for operator ruling
### Returns
- `acceptance`: the operator's ruling
### Execution
```prose
let acceptance = await gate("operator reads the sheet and rules per item")
return acceptance

Then attempt `prose lint gate-demo.prose.md` strictly against `prosescript.md`'s grammar productions: no production matches the `gate` call (it is not a declared function, block, session, or std/ library form). Yet per prose.md's table this is the documented protocol shape.

**Evidence (verbatim):**

`grep -n 'gate' skills/open-prose/prosescript.md`:

122:shape_property ::= ("self" | "delegates" | "prohibited") ":" expression NEWLINE
316:instance, or to a delegated helper the render declares. Inside pattern
361:| shape | Indented map with self, delegates, and prohibited behavioral boundaries |
786:used dependency, or a std/ library function) or to a delegated helper the

`skills/open-prose/prose.md` §"Relationship to gate()":

| | gate() | Runtime delegation |
| Yields to | A human reviewer | Another service |
| Resumes with | Human response | Delegate output file path |
| Blocking | Indefinite (waits for human) | Bounded (delegate session completes) |
| Protocol | await gate(payload) → response | Delegate: line → response path |

**Suggested fix (take or leave):** add a `gate_expression ::= "await"? "gate" "(" expression ")"` production (or whichever form is intended) to prosescript.md with a two-line semantics note and one example; or, if bare-statement `gate "..."` is also intended, say so. Given human-approval gates are the primitive agents reach for most when encoding operator authority, this is arguably the highest-leverage two-paragraph addition available. Mildly noteworthy: the primitive with the thinnest spec in the skill is the human-authority one.

**Environment:**

- OS: macOS (Darwin 24.x)
- Agent & model: pi harness; model per harness session telemetry: `claude-fable-5` (tool-derived from the session log, not self-reported — self-reported model IDs proved unreliable in this same run)
- Skill: open-prose v0.15.0, runtime_contract 2 (byte-identical to current `main` SKILL.md as of 2026-07-05)
- No reactor CLI involved (pure skill/docs issue); Node n/a
- Install method: `npx skills add openprose/prose --agent pi` (skill at `~/.pi/agent/skills/open-prose/`)

**What I already tried:** searched open+closed issues for `gate`, `prosescript grammar` (36 hits, all CI/lint/merge-gate senses, zero on this); read prosescript.md grammar productions in full; read prose.md §§ runtime delegation + Relationship to gate(); confirmed the extractor contract's gate mandate; reconciled three divergent gate surface forms across one generation+review cycle using the comparison table as the only oracle.