Proposal (rationale)

From F-019, found by WI-057 executing a self-test fixture that had never run.

modules/backlog/module.toml declares:

[skills.work-item]
extensions = { disable-model-invocation = true }
extension_note = """
`work-item` creates branches and merges. A model should not decide on its own that now is the
moment. …
"""

grep -n extensions src/*.ts returned nothing. So:

• [skills.<name>] was never parsed — Manifest had no skills field;
• the key never reached the emitted SKILL.md;
• extensions_allowed_from, declared in the skills gate table, was read by no engine;
• and modules/README.md documented the mechanism to contributors.

work-item creates branches and merges, and the manifest’s stated reason for opting it out of model invocation had been inert since it was written. The fifth instance of a rule configured and unread — and the most complete, because it was missing at every layer rather than one.

Decision

accepted — 2026-08-16, directed by the user.

Plan

Requirements

• [skills.<name>].extensions is parsed into the manifest.
• An opted-in extension is written into the emitted SKILL.md frontmatter.
• A skill with no opt-in is untouched.
• The gate treats an opted-in key as legal and still refuses one nobody opted into.
• The opt-in is read from the module, not the consumer repo.

Impacts

• src/types.ts, src/manifest.ts, src/add.ts, src/engines.ts.
• Every consumer’s work-item skill gains the key on next install.

Approach

Inject at emit rather than storing the key in the source skill. That is the point of the opt-in: the source stays spec-pure and portable (ADR-0001), and the extension — with its portability cost — stays attached to the module’s decision to take it.

Acceptance criteria / tests

1. A scratch install emits disable-model-invocation into work-item and not into backlog-summary.
2. The gate accepts an opted-in key, refuses one nobody opted into, and refuses it again when the rule is absent.
3. rungs check, npm test pass.

Out of scope

• New extensions for other skills. This implements the mechanism; using it is a per-module decision with a cost to state.

Execution

Branch feature/WI-058-skill-extensions, cut from main at fd16e07.

Four layers, because it was missing from four: parse [skills.*] into Manifest.skills; inject opted-in keys into emitted skill frontmatter; teach frontmatter-schema to consult the owning module; export the engine so the behaviour can be tested directly.

Two code paths emit skills, and patching one was not enough

emittedFiles and addModule both read modules/<m>/skills/** and write it out — the same file, produced twice. Patching only emittedFiles left add writing the un-extended version, so an install and an upgrade would have produced different content for the same skill, and the divergence machinery would then have reported the user’s file as diverged from something they never touched. Caught by installing into a scratch repo and finding the key still absent. Both paths now go through one helper.

The opt-in is read from the CLI’s module set, not the consumer’s files, so a repo cannot legalise an extension by editing its own copy — the portability cost belongs to whoever took it.

Review

Verified 2026-08-16.

1 · A scratch install emits it, selectively. rungs init <tmp> tracked:

The emitted frontmatter ends start to finish. / disable-model-invocation: true / ---. Met.

2 · The gate accepts, refuses, and refuses without the rule. Three assertions, because the first alone would be satisfied by a gate that accepts everything:

• opted-in key with extensions_opted_in set → no finding;
• argument-hint with nothing opted in → non-spec key 'argument-hint';
• the same opted-in key with extensions_allowed_from removed → reported again.

Met.

3 · Gates and tests. rungs check 24 pass · 0 fail · 0 unimplemented · 0 error; npm test 24 pass, up from 22. rungs modules audits clean. Met.

This repo’s own copy

.claude/skills/work-item/SKILL.md is a kept file — authored here before rungs was installed — so upgrade correctly refuses to touch it, and the key was added by hand to match the module’s declaration. Correct behaviour on rungs’ part, worth naming: the mechanism now works for every consumer that installs, and this repo had to opt itself in like anyone else editing their own file.