ObligationDeclaration

What a conformance harness says about one injectable obligation of SeamConformanceSuite — the mid-session transport death, the membership drain, the self-dial.

Why this exists

Each of those obligations is gated on a harness hook rather than a fabric SeamCapabilities flag, and its accountability used to be a String?: a tracking URL meant "not implemented yet", null meant "proven". Two states, three situations. There was no way to say this obligation does not apply to this fabric, by design, so a by-design inapplicability had to be filed as an unimplemented gap — and 9 of the 16 harnesses routing at #1442's mid-session-death umbrella were exactly that.

That is not bookkeeping. An umbrella titled "harness has not implemented mid-session-death injection" tells a contributor burning the list down that the three kuilt-nw entries are unfinished work, and the obvious "fix" — making NwSeam latch Torn when it loses its remote — would undo #1513 and break redial. A comment in one harness is not what that reader reads; a declaration the suite enforces is (#2568).

The vacuity this type has to avoid, and how each arm pays for itself

CLAUDE.md: "an 'I cannot reach this state' opt-out moves the vacuity one level up, where it is harder to see." A NotApplicable arm the suite simply believed would be strictly worse than the tracked gap it replaces — it converts a visible, listed shortfall into an invisible, self-certified green. So no arm is taken on trust. Every arm, on all three obligations, is cross-checked against the harness's own injection hook, whose return value the harness cannot fake without actually injecting:

That last cell is the one asymmetry, and it is deliberate rather than an omission: a refutation needs a stimulus the suite can apply without the harness's help, and only the mid-session-death arm has one (make the counterpart depart). The membership-drain and self-dial declarations get the hook cross-check and the prose toll, and nothing more.

NotApplicable.ContractDiffers is the strong arm, and the strength is the point: a harness cannot claim its fabric deliberately answers the event differently without performing the event and being watched. It also inverts into a regression guard — the day someone re-introduces tear-on-peer-loss in NwSeam, NwConformanceTest's declaration goes red, because the fabric now satisfies an obligation the declaration says it deliberately does not.

What the arms cannot detect

• NotApplicable.NotConstructible is the honest weak arm. Nothing can prove a negative existential — "no injection of this event exists under this harness" — so what the suite does instead is refute the one way the claim is cheaply false, per obligation (for a mid-session death: if the survivor latches Torn when its counterpart leaves, then a tear is reachable here and the stated reason is wrong). A harness that could inject the event through some other route it simply has not written is indistinguishable from one that genuinely cannot — and that distinction is exactly what Gap is for. Only the prose and a reader separate them.

• A refutation drawn from an absence is worth exactly as much as the stimulus behind it — the trap this vocabulary itself fell into on review, and the reason SeamConformanceSuite.departCounterpart is a hook rather than a hardcoded joiner.close(). The no-tear conclusion is identical whether the topology survived a departure or no departure ever happened: MuxServerLoomConformanceTest's joiner is a channel view whose close() departs nobody (#2665), so the arm was green by absence. The suite now asserts the counterpart really left the survivor's roster first, and a harness whose counterpart cannot be made to depart may not use this arm at all.

• NotApplicable.ContractDiffers's deviation check is a bounded negative observation (the postcondition did not hold within a window). Under runTest's virtual clock that window is virtual, which is strong for an in-process fabric — every eligible continuation runs before the bound expires — and weaker for a real-IO harness, where the deviation is asserted before the real transport has necessarily had wall-clock time to answer. It cannot catch a fabric that tears eventually, only one that tears promptly.

• Gap says nothing about whether the URL leads anywhere. It is the same toll SeamConformanceSuite.everyFalseCapabilityDeclaresAGap charges a capability gap: a sentence a reviewer can go and read.

• Every arm's prose is unchecked. A harness that declares the right arm for the wrong reason passes. The arm constrains the shape of the claim and the hook constrains its consistency; the reason is for the human.

Inheritors