# Description of Changes

<!-- Please describe your change, mention any related tickets, and so on
here. -->

This PR adds support for nested C# submodules. Multiple independent
instances of the same module assembly can be mounted independently of
each other (for example: submodule `A` can mount submodule `C` and
submodule `B` can also mount it's own submodule `C`).
- Route tables, indexes, reducers, procedures, and views to the correct
module instance.
- Add `ctx.As` for passing an instance-selected context to functions
that receive context.
- Add instance-aware `ctx.From` query builders.
- Add context-aware immediate scheduling overloads for reducers and
procedures.
- Add nested namespace paths in generated C# client queries (for example
`ctx.Db.SubmoduleA.SubmoduleC.{...}`).

# API and ABI breaking changes

<!-- If this is an API or ABI breaking change, please apply the
corresponding GitHub label. -->

No breaking changes.
This PR extends what we added in
#5974 but everything
stays compatible. Before, if a submodule mounted a submodule, that would
throw an error; now it's supported.

# Rollback safety impact

<!--
If this PR is safe to roll back after deployment and has no impact on
the rollback safety of any prior PRs, write `n/a` below.

Otherwise, list every prerequisite PR that must be included in a release
before this PR can merge. This PR must not be deployed until each
prerequisite has been deployed and sufficiently observed or tested in
the live deployment that we are confident it will not be rolled back.
Supported forms include #123, SpacetimeDB#123,
#123, and GitHub PR URLs.

Consider whether this PR:
- newly writes to a previously introduced but unused ControlDB table or
reducer, system table, or on-disk data format; or
- clears, deletes, incompatibly changes, or renders unsupported a
previously available ControlDB table or reducer, system table, or
on-disk data format.
-->

n/a

# Expected complexity level and risk

<!--
How complicated do you think these changes are? Grade on a scale from 1
to 5,
where 1 is a trivial change, and 5 is a deep-reaching and complex
change.

This complexity rating applies not only to the complexity apparent in
the diff,
but also to its interactions with existing and future code.

If you answered more than a 2, explain what is complex about the PR,
and what other components it interacts with in potentially concerning
ways. -->

4/5. This PR touches a lot of things: it changes module composition,
generated accessors, function dispatch, runtime context handling, SQL
name generation...

# Testing

<!-- Describe any testing you've done, and any testing you'd like your
reviewers to do,
so that you're confident that all the changes work as expected! -->

I added generator diagnostics and snapshot coverage, a nested-module
host integration fixture, and client regressions targeting .NET 8 and
.NET 10. Coverage includes independent tables and caches, deep namespace
paths, dispatch, queries and joins, context selection, transaction
commit/rollback, and immediate scheduling.

 - [ ] Run C# generator tests on .NET 8 and .NET 10.
 - [ ] Run the namespace_csharp standalone integration tests.
- [ ] Run the C# client regression harness against the updated local SDK
packages.

---------

Signed-off-by: Alessandro Asoni <alessandro@clockworklabs.io>
Co-authored-by: clockwork-labs-bot <clockwork-labs-bot@users.noreply.github.com>
Co-authored-by: Alessandro Asoni <alessandro@clockworklabs.io>