Update snapshot and projects on file close

[gabritto]

Fixes #3676.
We were missing a couple things to make this scenario work:

• Update snapshots on didClose so that we don't wait until a request comes in to clean up tsconfig diagnostics
• Clean up closed projects on file close during project collection build.

Note we'll always clean up tsconfig diagnostics once all files in that project are closed, even if the tsconfig.json remains open. We may want to have the server handle .json files in the future (though we'd still have push diagnostics, but only for global diagnostics and not diagnostics specific to the tsconfig itself).

[Copilot]

Pull request overview

This PR fixes #3676 by ensuring tsconfig diagnostics are refreshed after the last TS/JS file in a project is closed. Previously, snapshot updates (and project cleanup) were deferred until the next request arrived, leaving stale tsconfig diagnostics displayed to the user.

Changes:

• Added a debounced ScheduleSnapshotUpdate mechanism (mirroring ScheduleDiagnosticsRefresh) and invoke it from DidCloseFile to flush pending close events after a short delay.
• Extended ProjectCollectionBuilder.DidChangeFiles to also run the open/closed-file project retention pass when only files have been closed, so abandoned configured projects are deleted.
• Cancel any scheduled snapshot update from all paths that take snapshotUpdateMu (DidOpen, getSnapshot, idle cache clean, API entry points, Session.Close).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/project/session.go	Adds UpdateReasonDidCloseFile, ScheduleSnapshotUpdate/cancelScheduledSnapshotUpdate, and wires DidCloseFile to schedule a debounced update; cancels scheduled updates from other update paths and Close.
internal/project/snapshot.go	Adds logging for the new UpdateReasonDidCloseFile reason.
internal/project/projectcollectionbuilder.go	Runs the open/close project-retention loop when files are closed (not just opened) so closed projects are removed.
internal/project/api.go	Cancels any scheduled snapshot update on API open/update entry points.
internal/project/project_test.go	Adds publishDiagnosticsCall helper and a regression test verifying tsconfig diagnostics are cleared after the last TS file is closed.

[andrewbranch]

I know in Strada, we intentionally don't close projects on file close, because it would be wasteful if the next action you took was to open another file in the same project... but presumably, tsconfig diagnostics also work basically the way we want in Strada. How does that work?

[gabritto]

I know in Strada, we intentionally don't close projects on file close, because it would be wasteful if the next action you took was to open another file in the same project... but presumably, tsconfig diagnostics also work basically the way we want in Strada. How does that work?

Apparently we don't clean up config diagnostics on project close in Strada. 🙁

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.