chore: bump the target engine to v1.0.0-beta.10

[TomChv]

Everything this repo ships is pinned to one engine release, so a bump moves four
things together, and skipping any of them is silent: the vendored library
sources, its generated bindings, the bundle built from them, and the Go
generator.

Re-vendored from the tag. beta.10 changes the library's introspector and its
registry, and adds agent to the module-facing index.ts — the same export whose
absence at beta.9 would have left modules unable to resolve it, caught again
here by the check that every re-export exists in the bundle.

The generator moved too, and three-way merged cleanly against our local changes:
@agent support in the entrypoint, nullable objects gated on a beta.10 cutover,
and the extendable-type list dropping Binding and Env. Left unsynced, that last
one would have generated augmentations for types the engine no longer has.

tsdistconsts is unchanged, so the typescript pin and bun image digest hold.

The workspace also pins sdk-sdk's CLI release to match. dagger/sdk-sdk#20 threads
the configured release through to the contract checks, which previously ran
mod-test's own pinned default and so paired this SDK's beta.10 bundle with a
beta.9 engine; all 22 contract-suite checks pass again. The pin stays even though
sdk-sdk's default matches ours today, because this SDK ships a library built for
one engine release, so the version the harness runs is load-bearing.

Also records what fork.withDirectory actually does. The client-bundle design
leaned on it being an overlay, which it is not: the polyfill documents it as
"add or replace" and the replace is real in the changeset's after tree. What
makes client regeneration safe is that a client changeset is only ever applied
to disk, and applying is additive. Module generation stages its changeset into a
workspace and reads it back, where unstaged files — the module's own config and
source — do disappear; hence the diff-based staging it uses instead. Verified
rather than reasoned: a client directory holding a vendored sdk/core.js and an
unrelated NOTES.md keeps both across a regeneration, with removedPaths empty.

Signed-off-by: Tom Chauveau tom@dagger.io

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