Purpose Properties Skill

Retrofit and re-derive entry point for purpose.yml#purpose_properties. For new projects this runs inside /mycelium:start Step 3b. Use this skill when:

• The project existed before v0.120.0 and has no purpose_properties (the retrofit case — every project created before that release, since /mycelium:start Step 4 exits for already-initialized projects and never reaches the extraction).
• why, how or what changed, so derived_from_hash no longer matches and every stance below it is superseded (the drift case — this is the one that matters most and the easiest to skip).
• A property list exists but the user wants to revisit which properties are binding.

Full contract: ${CLAUDE_PLUGIN_ROOT}/../../docs/purpose-stance.md.

Step 1: Read the current state and say which case this is

Read purpose.yml. Then say plainly which of these you are in, because the three have different consequences and the user should not have to infer it:

• No purpose_properties → retrofit. Nothing below has ever been checked against the purpose.
• Hash mismatch → drift. Report it as "your purpose changed after these were derived, so every purpose_stance below them was reasoned under a definition you have since changed." This is the state that quietly invalidates work; name it in those terms.
• Hash matches → nothing to do. Report the property count and stop. Do not re-derive for tidiness.

Step 2: Attempt extraction, and classify what fails

For every element of why, how and what, ask: can I name a specific solution that would CONTRADICT this?

• Yes → candidate property. Record property, verbatim (their words, not yours), source, and the contradicting solution in contradicted_by.
• No → do not force one. Quality adjectives — secure, accessible, fast, simple, delightful, robust — yield nothing checkable, because every candidate solution claims to satisfy them.

Measured 2026-08-23, blind: "accessible and secure" produced no checkable property, while five abstract framework principles produced clean ones. The axis is not abstract vs concrete — it is quality adjective vs structural claim. Do not treat concrete-sounding words as safe.

Step 2a: Screen for quality adjectives BEFORE trusting your own refusal

DO NOT RELY ON NOTICING. Step 2 says a quality adjective yields nothing checkable and asks you to decline. The evidence that an extractor actually declines is one blind run, one model family — the 2026-08-23 test, where the extractor returned NONE for "accessible and secure" unprompted. That result is real and it is thin, and this skill runs under model families that test never touched, in runtimes where no hook fires to catch the difference. A model that does not refuse produces a confident property, marks it binding, and creates a stance field that every solution answers preserves forever — populated, green, and meaningless. The mechanism's own failure mode, at its entry point.

So the screen is a rule, not a judgement:

TRIGGER LIST — if an element contains any of these words, it routes to Step 3 REGARDLESS of whether you extracted something from it:

secure · safe · private · accessible · usable · intuitive · simple · easy · fast · performant · scalable · reliable · robust · flexible · modern · seamless · delightful · high-quality · best-in-class · efficient · powerful · lightweight

Extracting a property from one of these words is not evidence the word was checkable. It is the predicted failure. Route it, let the builder supply the standard, and record what they say.

AND THE GENERAL TEST, for words the list does not carry (it cannot be complete, and treating it as complete is the next version of this bug):

Would every plausible competing solution ALSO claim to satisfy this? If yes, it is a quality adjective, whatever it sounds like. Route it.

"Secure" fails that test — nobody proposes an insecure login. "Anonymous" passes it — a solution requiring an account plainly does not claim anonymity. Note that the concrete-sounding word is the one that fails. The axis is never how technical the word looks.

WHAT IS STILL UNTESTED, stated so nobody reads the list as coverage: whether a builder actually answers the Step 3 prompt. The 2026-08-23 run exercised extraction only — no builder was asked anything — so the recovery path has evidence for its necessity and none for its effectiveness.

Step 2b: Check the ALTITUDE of every candidate before you record it

A property must sit at the altitude where violation is meaningful. Ask, of each candidate:

What would have to be true for this to be violated — a single move, or a design choice?

• A design choice → it is a property of the product. Record it.
• A single move → you have extracted a rule about BEHAVIOUR, not a property of the product. Do not record it. A property that can be violated by one sentence turns the stance field into a footnote requirement, and a check people must satisfy per action is one they mute.

WORKED EXAMPLE, and it is why this step exists. From "Theory-guided decisions: every significant decision is grounded in established frameworks", two independent blind extractions BOTH produced "a significant decision must name the framework it rests on" — per decision. The words invite it. But the founder's reading is the right one: not everything needs to be grounded for the overall to be grounded. The principle is about how the SYSTEM is built — its gates, skills and structure derive from theory — not about an audit trail on each move. Pitched per-decision it is micromanagement; the same project's (per: <source>) convention, injected into every session, sits at 4 citations across 197 decision-log entries.

AND CHECK WHETHER IT IS ALREADY MECHANISED BEFORE MINTING A PROPERTY. That same principle is already enforced at the right altitude by check_theory_fidelity.py on every push. Point at the existing check; do not mint a property that duplicates it — two mechanisms for one claim means one of them drifts unnoticed.

binding and altitude guard different failures. binding: true limits HOW MANY properties are checked. Altitude limits how GRANULAR each one is. Both end the same way if you get them wrong — a check nobody reads — and only one of them is visible in the field.

Step 3: Interview the builder on what failed — with candidates, not an open question

You said "secure". Which of these would you call a violation? (a) passwords stored in plaintext (b) no transport encryption (c) sessions that never expire (d) something else

Recognition is cheap; generation is not. Offer three plausible violations drawn from the domain, and expect (d) to be where the real answer lives.

• They answer → you have a property; record the violation in contradicted_by.
• They cannot, or decline → record aspiration_reason and say the consequence out loud: "'secure' stays undefined, so no solution will ever be checked against it." A skip is a recorded choice, never a blank.

This is NOT /mycelium:user-interview. That skill asks about specific past behaviour, which is right for discovering user needs and wrong here — this elicits a definition from the builder about their own intent, where the question is hypothetical by design.

Step 4: The user marks binding, and only they can

Present the candidates and ask which ones, if violated, would break the product rather than merely disappoint. Only those get binding: true, and only those are ever checked.

Do not set these yourself. A why/how/what yields many adjectives; an agent marking them all binding turns the check into noise, and noise gets muted. Set confirmed_by: human only after they have actually answered.

IF THEY REJECT THE BOOLEAN, THEY ARE PARTLY RIGHT — DO NOT TALK THEM OUT OF IT. A builder on 2026-08-31 answered: "I have problem seeing them as booleans. They have a value (say 1-10), and then can be weighed against each other." The resolution is better than either frame, and the day produced all three categories:

• Constraints — violate it and the thing is out, no compensation. binding: true.
• Weighted criteria — most properties. Set weight 1-10 and leave binding: false. No checker reads weight; it is for the human's own trade-offs, and saying so plainly is what keeps the field honest.
• Constraints with a named unlock — the most useful category, and the one nobody asks for unprompted. Not eternal, not tradeable, changeable through one specified event.

Why not simply switch to weights. A pure weighted score permits compensatory trade-offs, so a high total can outvote a violated must — that is exactly how someone accepts a role that pays well and requires the relocation they called non-negotiable. binding is guarding something real. Keep it as the compensation gate and let weight carry everything else.

Asking for the unlock. For each binding: true property, ask: "is there anything that would legitimately change this, and what exactly would have to happen?" Record it as unlock.state.

THE UNLOCK MUST BE AN EVENT, NOT A MOOD. Worked example: a "Steinkjer base" constraint unlocks on a family conversation held and logged — explicitly NOT on income pressure. An unlock that fires "when things get bad enough" is indistinguishable from erosion, and it fires exactly when judgement is worst. If they cannot name an observable event, the property has no unlock. Leave it off rather than writing a soft one; a soft unlock is worse than none because it launders a broken constraint as a planned one.

Only binding: true properties are checked, exactly as before. Weights and unlocks change what the canvas can RECORD, not what the gate enforces.

Step 5: Write, then say what changed downstream

Write purpose_properties to purpose.yml (Read before Write, per the canonical rule). Set derived_from_hash by running:

python3 "${CLAUDE_PLUGIN_ROOT}/scripts/check_purpose_stance.py" --canvas-dir .claude/canvas

On a re-derive, tell them what it invalidated: every existing purpose_stance was reasoned under the old definition and now needs re-reading. Do not silently leave stale stances looking current.

What this skill does NOT do

• It does not judge whether a solution serves the purpose. Nothing in Mycelium does; that judgement is unreliable and a checker that unreliable is a second opinion wearing a gate's clothes.
• It does not write a stance on any solution. That belongs to /mycelium:ost-builder.
• It does not clear a contradicts. Only a human can, and the check enforces it.

Theory grounding

Sinek (Start With Why) — the why/how/what ordering, and the reason the innermost ring governs the others. Used as an ordering, never for the book's neuroscience claims, which do not survive checking. The mechanism itself is this project's own: a declaration that can be checked, rather than an alignment that cannot.