Add the external-calls deep dive

[angelol]

Adds an External Calls page under Deep Dives, next to the External Signing group, and registers it in the navigation.

This is the port of digital-asset/canton#652, which was written and reviewed there but held open once rst files were frozen in favor of this repo (context: digital-asset/canton#644 (comment)). Changes relative to the rst: the Sphinx literalinclude of the participant config snippet is inlined as a code block, the :ref: cross-references point at the corresponding pages here (external-signing-hashing-algorithm, error-codes), and the early-access warning now names the concrete versions (protocol version 36, LF 2.4).

mint broken-links reports no issues in the new page (the 13 pre-existing findings are in unrelated files).

[shreyas-da]

Adding @rgugliel-da & @soren-da to review as they were tagged on the original PR.

[rgugliel-da]

Adding @rgugliel-da & @soren-da to review as they were tagged on the original PR.

Thanks. I asked @thibault-da to review, has he is more knowledgeable than I am.

[paulbrauner-da]

I don't understand why we're not seeing a link to a mintlify preview for this PR (like we did in #971 for instance). I'll ask around. In the meantime @angelol it seems like you need to add Signed-off-by to your commits, see https://github.com/canton-network/cf-docs/pull/1577/checks?check_run_id=101990688191.

[angelol]

Signed off and repushed — DCO is green now.

[paulbrauner-da]

It generally looks good to me but I have a few comments:

• It is a mix of very practical information, like how to configure your participant, and theoretical concerns like the trust model and the verification step of the protocol. Maybe it should be split into two different articles? Not a must, but would maybe help reach the relevant audiences better.
• The article keeps mentioning "raising an alarm" but there's not such concept in canton. Does it translate into a warning in the logs? An error?
• Some information seems to be presented a bit backwards: the explanation of the daml signature assumes you know what config is, but it is only presented in the next section.
• There is no, as far as I could tell, explanation of who the confirming parties are for a given call
• I think a concrete example of a call would be a good introduction to the part of the article that deals in practicalities