Use Workspace.withDirectory for init and client codegen once beta.11 is out

[TomChv]

Blocked on the v1.0.0-beta.11 release.

dagger/dagger#13956 (fixes dagger/dagger#13955 — the engine issue #35 said was worth filing) splits Workspace.withNewDirectory in two:

• withNewDirectory now replaces whatever the path held, on every workspace kind — host-backed, value and git alike. The local/git divergence that cost Keep existing files when init and client codegen write a directory #35 two red CI rounds is gone.
• The new Workspace.withDirectory merges the source onto what the path already holds, the same contract Directory.withDirectory has.

Both workarounds #35 had to write — the read-back-and-layer, and pruning the bindings twice — are that second field, so they can go away.

What to change

Once dagger.json moves to engineVersion: v1.0.0-beta.11:

initModule (typescript-sdk.dang:234)

# withNewDirectory replaces the directory it writes, so layer the starter
# onto what is already there: init must never remove a user's files, nor
# the config the engine wrote at `modPath` before calling us.
ws.withNewDirectory(
  "/" + modPath,
  existingDir(ws, modPath).withDirectory(".", templateSource),
).changes(ws)

becomes ws.withDirectory("/" + modPath, templateSource).changes(ws), and that half of the comment goes with it. The modPath anchoring note above it still applies and should stay.

generateClient (typescript-sdk.dang:620) and generateAllClient (typescript-sdk.dang:687)

withoutClientBindings(ws, path)
  .withNewDirectory("/" + path, existingClientBase(ws, path).withDirectory(".", generated))
  .changes(ws)

should collapse to pruning the stale bindings out of the workspace and merging the generated package on top:

withoutClientBindings(ws, path)
  .withDirectory("/" + path, generated)
  .changes(ws)

That keeps the ownership split #9 established — the SDK owns *.gen.ts, the user owns everything else — with one prune instead of two.

Then:

• existingClientBase (typescript-sdk.dang:566) becomes dead — delete it.
• withoutClientBindings' doc comment (typescript-sdk.dang:573) is the "pruning has to happen twice" explanation. It describes a divergence that no longer exists; it should shrink to what the helper does.
• existingDir stays: clientBindings still reads the destination through it.
• In generateAllClient, the reason the baseline read from the untouched ws while the prune ran on stagedWs was that reading back out of a pruned host-backed workspace came up empty. With no read-back left there is nothing to keep straight — but the fold still needs its prune on stagedWs, so verify rather than assume.

Guards

dagger check 'e-2-e*' — the three checks #35 added exist for this and should all still pass:

• init:init-over-existing-check
• client:generate-client-respects-existing-check (main.ts survives, stale-dep.gen.ts is pruned)
• client:generate-client-on-synthetic-workspace-check

The last one was there to catch the local/git split. It is worth keeping even though the engine no longer diverges.