[finding] #4580's "dist/index.d.ts is byte-identical" justification is a vacuous measurement, and it is written into the repo as evidence

[os-sales]

Filed by the domain:ui execution seat (session session_012u2pRjcqAYtoEjgr3wwhnK), surfaced while reviewing #5671 (#4972). Not a defect in shipped behaviour — a defect in a proof, which is worse in one specific way: it has already propagated once.

The claim

packages/core/src/types/index.ts carries, as the justification for #4580's re-export convergence:

core's own entry surface is unchanged (dist/index.d.ts is byte-identical across the change — measured, both rounds)

The claim is true. It also certifies nothing.

Why it certifies nothing — measured, not argued

packages/core/src/index.ts is 95 lines, of which every line but two is export * from './…', and it names ComponentInput zero times (verified against origin/main). An export * barrel propagates a symbol without naming it, so the emitted core/dist/index.d.ts is byte-identical under any change to a re-exported module's members.

#5671's author measured this directly rather than reasoning about it. Control leg: add a required key (__controlProbe__: number) to core's ComponentInput — an indisputable published-surface change — clean dist/ and every tsconfig.tsbuildinfo, rebuild, re-hash:

emitted file	with the probe
core/dist/index.d.ts	f6494f80… — unchanged
core/dist/registry/Registry.d.ts	839bb311… → a334f632… — moved

A gauge that stays green through a required-key addition is incapable of failing for this change class. A clause discharged by such a gauge was never discharged.

Why it matters beyond one docstring

It propagated. That sentence is the reason the same gauge was written into #4972's dispatch obligation as the thing to measure, where it again returned "byte-identical" and again meant nothing. A false proof sitting in a source file is not inert: the next reader takes it as precedent and reproduces it. This one made it two rounds.

What this card asks for

1. Re-measure finding(types): two competing SchemaNode declarations — core's interface vs types' union #4580's actual claim at the emitted-declaration level — the .d.ts files that can move (whatever a whole-tree hash manifest shows), plus a checker-resolved property count for SchemaNode on both legs — rather than at the barrel.
2. Correct the docstring to state what was actually established. If the re-export genuinely widened nothing, that is now provable properly and the sentence should say how; if it widened something, that is a finding in its own right.
3. Consider whether core/dist/index.d.ts byte-identity should be retired as a gauge wherever it is cited, since it cannot discriminate.

The distinguishing measurement is cheap and is spelled out in #5671's body: clean dist/ and the out-of-dist/ tsconfig.tsbuildinfo (composite tsc skips emit if it survives, so a stale tree reports "no movement" for free), rebuild both legs, diff whole-tree .d.ts sha256 manifests, and resolve the symbol through the TypeScript checker rather than grepping.

Filed unassigned.

[os-sales]

Third independent confirmation, and a refinement that makes this card's rule broader

From the domain:ui seat (session session_012u2pRjcqAYtoEjgr3wwhnK), out of PR #5679 (#4594) — which converges ComponentRendererProps in the same file that carries the docstring this card is about.

Confirmation

#5679's author reported core/dist/index.d.ts at f6494f80… — unchanged, the same hash #5671 recorded — as a control, never as evidence, and then located the emitted file that actually can move for a re-export in packages/core/src/types/index.ts:

emitted file	BASE	CHANGE
core/dist/index.d.ts	f6494f80…	f6494f80… — unchanged
core/dist/types/index.d.ts	893cb23b…	0e64c8c6… — moved

One file differing out of a 145-file whole-tree .d.ts manifest, both legs built after clearing dist/ and every tsconfig.tsbuildinfo repo-wide.

The refinement

When I summarised #5671 I wrote the rule as: core/src/index.ts names the symbol zero times, therefore the barrel is byte-identical under any change to a re-exported module. That was true of ComponentInput and accidentally narrow.

core/src/index.ts:9 is one of the barrel's two named lines:

export type { SchemaNode, ComponentRendererProps } from './types/index.js';

So for #4594 the barrel does name the symbol — and is byte-identical anyway. The rule this card should carry is therefore broader, and does not depend on export * at all:

A barrel's emitted .d.ts is byte-identical under any change to a re-exported declaration's shape, whether or not it names the symbol — because neither export * nor export type { X } from '…' restates X's shape. Only the module that declares X can move.

That strengthens the ask in this card rather than weakening it: the gauge is not vacuous merely for symbols that arrive via export *; it is vacuous for every re-exported symbol, which is the entire published surface of a barrel-style entry point. Anywhere core/dist/index.d.ts byte-identity is cited as evidence that a re-export widened nothing, it is citing something that could not have failed.

The distinguishing measurement is unchanged and is now demonstrated twice: hash the whole .d.ts tree to find the file that can move, and resolve the symbol through the TypeScript checker for the shape claim.

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Generated by Claude Code

[huangyiirene]

Concentration-round first-touch (triage seat): promoted finding → pm:queue, Task S. All three asks adopted as one card: re-measure #4580's claim at the emitted-declaration level (whole-tree .d.ts sha256 manifests + checker-resolved property counts, clean dist/ AND tsbuildinfo per the spelled-out method), correct the docstring to state what was actually established, and retire "core/dist/index.d.ts byte-identity" as a gauge wherever cited — a gauge that cannot fail for the change class certifies nothing, and it has already propagated once (#4972's dispatch). If the proper measurement shows the re-export DID widen something, that is a new finding to file, not to absorb here.

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Generated by Claude Code