[Kinflou]

A new proposal, proposals/extensibility.md (status: under discussion), tracked in core#120.

• One mechanism: official encodings are defined the same way as third-party ones. "Official" means maintained here and shipped by default.
• An encoding is a definition: a versioned name (bare when official, namespaced otherwise), a profile and vectors. The corpus format and the profile schema become a public spec, and the conformance runner becomes a reusable library.
• Discovery: core learns about a third-party encoding from a dependency's config.idp, and trusts its profile like the dependency's schemas.
• Generated code: comline.toml maps each encoding to a type per target. An unmapped encoding is an error, never a fallback, and the per-package format trait (generation#67) isn't sealed.
• Limit: a format can't need more than the generated data model.
• Transports and dispatchers stay runtime-only, with documented patterns (middleware by wrapping Dispatch).
• Generators stay a separate question (core#8).
• The schema-compatibility proposal's open question on third-party profiles now points here.

zensical build --strict passes.

Second commit: handshakes and unchecked (core#121, runtime#18)

• Handshakes become a third declared axis: comline@1, none, and namespaced custom ones. They're chosen per protocol with @handshake, and their profile states what they verify. runtime#15 becomes comline@2.
• Unchecked marks giving up a guarantee Comline makes between peers: a weaker handshake, an unproven encoding, a version-rule override, or skipping checks at runtime (*_unchecked). It's written @unchecked = "reason". It's off by default (annotations.unchecked.allowed), required where it applies, and a warning where it doesn't. Consumers accept it per protocol in config.idp. Making a protocol unchecked is major.
• Schema compatibility gets rows for @handshake and @unchecked, and its escape-hatch question now points to unchecked.

Third commit: marking a given-up guarantee, four options

• Wording: "a weaker handshake" was the wrong axis. A custom handshake may do more than Comline's; what matters is whether it establishes the guarantees Comline relies on. The extensibility page now names the four guarantees (schema agreement, encoding agreement, encoding conformance, version honesty) and states the rules around the marker without naming it.

• proposals/guarantee-marker/: four competing proposals for the marker, each with its case for and against:

  • A: @waives(guarantee = "…")
  • B: @assumes(guarantee = "…")
  • C: @unverified = "…"
  • D: keep @unchecked

  The index separates the two underlying choices: whether the marker names the guarantee, and which word.