fix(project): re-read cached file contents on didChangeWatchedFiles Created event

[erantianantha]

Fixes #64195

Summary

When workspace/didChangeWatchedFiles reports a Created (type 1) event for a file that is already loaded in the program (for example, during an atomic save where an editor writes to a temporary file and renames it over the target), snapshotFSBuilder.markDirtyFiles previously only inspected change.Changed. Consequently, s.diskFiles retained the stale cached file content and hash, causing stale diagnostics to persist indefinitely until server restart or explicit didOpen.

Changes

1. snapshotFSBuilder.markDirtyFiles: Process change.Created in addition to change.Changed. If a created file path was already cached in s.diskFiles, reload its entry from disk via reloadEntryIfContentChanged so that updated contents and hash are reflected in the snapshot.
2. snapshotFSBuilder.watchChangesOverlapCache: Include change.Created in cache overlap checks for excessive watch events.
3. SnapshotFS.expandRealpathAliases: Expand node_modules symlink aliases for change.Created events as well.
4. overlayFS.processChanges: Recompute matchesDiskText for open overlays when a WatchCreate event occurs.
5. Added unit tests for atomic saves / create events on closed files and cached snapshot entries.

[Copilot]

🟡 Changes recommended

The unresolved save→create ordering issue can leave open overlays incorrectly marked as matching disk.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Fixes stale snapshots and diagnostics when atomic saves emit Created file-watcher events.

Changes:

• Reloads cached files for create events.
• Extends symlink alias and overlay handling.
• Adds snapshot, session, and overlay regression tests.

A moderate issue remains: a queued didSave can suppress later create handling, leaving stale overlay state. The save→create batch case must be handled and tested.

File summaries

File	Description
tsc/internal/project/snapshotfs.go	Handles created events in snapshot caches and aliases.
tsc/internal/project/snapshotfs_test.go	Tests cached-file reload behavior.
tsc/internal/project/session_test.go	Tests atomic-save scenarios end to end.
tsc/internal/project/overlayfs.go	Updates overlay disk-match state on creation.
tsc/internal/project/overlayfs_test.go	Tests overlay handling for create events.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Balanced

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