Code change:
the fact that there are applications using HTTP/3 datagrams enabled on this endpoint. <del> 9. </del> <ins> 8. 8.1. This document will request IANA to register the following entry in the "HTTP/3 Frames" registry: </ins> <del> 9.1. </del> <ins> 8.2. </ins> This document will request IANA to register the following entry in the "HTTP/3 Settings" registry: <del> 9.2. </del> <ins> 8.3. </ins> <del> This document will request IANA to register the "Datagram-Flow-Id" header field in the "Permanent Message Header Field Names" registry maintained at <<https://www.iana.org/assignments/message-headers>>. </del> <ins> This document establishes a registry for HTTP/3 frame type codes. The "HTTP Capsule Types" registry governs a 62-bit space. Registrations in this registry MUST include the following fields: Type: A name or label for the capsule type. The value of the Capsule Type field (see capsule-frame) is a 62bit integer. An optional reference to a specification for the type.  This field MAY be empty. Registrations follow the "First Come First Served" policy (see Section 4.4 of IANA-POLICY) where two registrations MUST NOT have the same Type. </ins> <del> 9.3. </del> <ins> This registry initially contains the following entries: </ins> <del> This document will request IANA to create an "HTTP Datagram Flow Parameters" registry.  Registrations in this registry MUST include the following fields: </del> <ins> 8.4. </ins> <del> The key of a parameter that is associated with a datagram flow list member (see header).  Keys MUST be valid structured field parameter keys (see Section 3.1.2 of STRUCT-FIELD). </del> <ins> REGISTER_DATAGRAM_CONTEXT capsules carry key-value pairs, see register-capsule.  This document will request IANA to create an "HTTP Datagram Context Extension Keys" registry.  Registrations in this registry MUST include the following fields: </ins> <del> A brief description of the parameter semantics, which MAY be a summary if a specification reference is provided. </del> <ins> The key (see register-capsule).  Keys MUST be valid tokens as defined in Section 3.2.6 of RFC7230. </ins> <del> This field MUST be either Yes or No.  Yes indicates that this parameter is the name of a named element (see header).  No indicates that it is a parameter that is not a name. </del> <ins> A brief description of the key semantics, which MAY be a summary if a specification reference is provided. </ins> An optional reference to a specification for the parameter.  This field MAY be empty.

Related discussion:
text: 2) Can the receiver of a flow-id assignment use that same flow-id when sending datagrams, or could this mean something completely different? I think the answer to (1) is "yes, it can tell me to stop" (i.e. it is negotiated while allowing speculative sending). For (2), I lean toward bidirectional, but not strongly. There are plenty of codepoints, so it seems wasteful for each endpoint to define the same semantic explicitly.
NAME the intent of this issue wan't to conflate those two things. This issue is about scope. For consent, see issue .
Conceptually, I like unidirectional better. I tell the peer that when I send with context-ID=X, it has a given semantic. For bidirectional the sender is saying both that and that if the peer sends on that ID the original sender will interpret with the same semantic. That might not even make sense. Is it possible to associate datagrams with a unidirectional stream (push?). If so, does allowing for bidirectional context imply that even though the receiver cannot send frames on the stream, it can send datagrams? Every negotiation does run the risk of loss/reordering resulting in a drop or buffering event at the receiver. The appeal of bidirectional is that it removes half of this risk in the cases where the bidirectionality is used.
To second NAME I would also prefer bidirectional without support for half-close. Given you can always not send something in one direction, and there's none of the overhead of streams(ie: flow control, etc) I can't see any benefits of unidirectional over bidirectional in this case. Associating h3-datagrams with a server push seems like unnecessary complexity to me, but you're right that it should be clarified.
During the 2021-04 MASQUE Interim, we discussed a design proposal from NAME to replace the one-layer flow ID design with a two-layer design. This design replaces the flow ID with two numbers: a stream ID and a context ID.