docs: define a seam as the (Service, Service provider, Consumer) trio

docs/subsystems/credentials.md

@@ -57,9 +57,9 @@ interface CredentialInfo {
 
 Generated from source by `scripts/gen-cordis-catalog.ts` (verified fresh by `pnpm run verify-cordis-catalog` in doc-sync; regenerate with `pnpm run gen-cordis-catalog`) — this section is byte-identical in both language sides of the page. Signature blocks use a `ts cordis-catalog` fence and keep the original source JSDoc; dispatch modes are defined in the [primer](../cordis-primer.md#dispatch-modes), and the framework-inherited `ctx` surface lives in [cordis-api/inherited.md](../cordis-api/inherited.md).
 
-<a id="ctxcredentials--credentials-abstract-seam"></a>
+<a id="ctxcredentials--credentials"></a>
 
-### `ctx.credentials` — `Credentials` (abstract seam)
+### `ctx.credentials` — `Credentials`
 
 Abstract credential service. Providers implement the four operations over their source layers; one seam-wide rule binds them all: an empty stored value is absent everywhere — `resolve` skips it, `describe` reports it unconfigured — so a blank never masquerades as a configured secret.