Watcher build mode efficiency updates

[johnfav03]

Refactors the tsc --build --watch functionality to use the new shared FileWatcher and trackingvfs structure from the CLI and LSP watchers, reducing code duplication and patching inefficiencies like redundant scanning of shared dependencies.

Note: this PR is built on the watcher-lsp-integration branch so only review commits from 0655dba onward

Fixes #2666

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Refactors watch/build-mode change detection to use a shared polling FileWatcher + trackingvfs approach (aligned with CLI/LSP), reducing redundant scanning and improving dependency change tracking (incl. package.json-driven resolution).

Changes:

• Reworked internal/vfs/vfswatch to watch directory sets (recursive + shallow), emit structured WatchEvents, and support context-aware settling.
• Updated build/watch orchestration to compute watched directories from SeenFiles + wildcard dirs and to use ScanForChanges() instead of per-file watch state.
• Added polling-watcher integration for LSP sessions plus new tests; updated baselines to reflect revised incremental out-of-date reasoning/log output.

Reviewed changes

Copilot reviewed 29 out of 29 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
testdata/baselines/reference/tsbuildWatch/sample/reportErrors-when-stopBuildOnErrors-is-passed-on-command-line.js	Updated expected watch output/error counts under new watcher behavior
testdata/baselines/reference/tsbuildWatch/sample/reportErrors-when-preserveWatchOutput-is-passed-on-command-line.js	Baseline update for watched buildinfo timestamp behavior
testdata/baselines/reference/tsbuildWatch/sample/reportErrors-when-preserveWatchOutput-is-not-used.js	Baseline update for watched buildinfo timestamp behavior
testdata/baselines/reference/tsbuildWatch/sample/incremental-updates-in-verbose-mode.js	Baseline update for “out of date because …” reasoning
testdata/baselines/reference/tsbuildWatch/reexport/Reports-errors-correctly.js	Baseline update for verbose out-of-date messaging
testdata/baselines/reference/tsbuildWatch/moduleResolution/resolves-specifier-in-output-declaration-file-from-referenced-project-correctly-with-cts-and-mts-extensions.js	Baseline updates adding incremental “file change detected” sections and revised reasons
testdata/baselines/reference/tsbuildWatch/moduleResolution/build-mode-watches-for-changes-to-package-json-main-fields.js	Baseline updates to reflect package.json watch behavior
testdata/baselines/reference/tsbuildWatch/demo/updates-with-bad-reference.js	Baseline update for error out-of-date messaging + buildinfo timestamps
testdata/baselines/reference/tsbuild/sample/sample.js	Baseline update for referenced-project input selection message
testdata/baselines/reference/tsbuild/sample/explainFiles.js	Baseline update for referenced-project input selection message
testdata/baselines/reference/tsbuild/commandLine/emitDeclarationOnly-on-commandline.js	Baseline update for referenced-project input selection message
internal/vfs/vfswatch/vfswatch_race_test.go	Updated race/fuzz tests for directory-based watcher + ScanForChanges()
internal/vfs/vfswatch/vfswatch_event_test.go	New tests validating WatchEvent create/change/delete behavior
internal/vfs/vfswatch/vfswatch.go	Major refactor: directory watchers, WatchEvent, logging, ctx-aware run/settle
internal/tspath/pathcomponents_watching_test.go	New tests for exported watch-specific path component logic
internal/tspath/path.go	Exported GetPathComponentsForWatching for common-parent watch coarsening
internal/project/watch_test.go	Moved watch-path-component tests out of project package
internal/project/watch.go	Added WatchedDirectories() extraction for polling watcher directory computation
internal/project/session.go	Added optional in-process polling watcher + directory updates per snapshot
internal/project/polling_watcher_test.go	New integration test for LSP polling watcher triggering diagnostics refresh
internal/project/configfileregistrybuilder.go	Switched GetCommonParents callback to tspath.GetPathComponentsForWatching
internal/lsp/server.go	Default polling enablement when client watching is unavailable + user opt-in
internal/ls/lsutil/userpreferences.go	Added usePollingWatcher user preference plumbing
internal/execute/watcher.go	Watch-mode now computes watched dirs + filters builds via WatchEvent relevance
internal/execute/tsctests/tscbuild_test.go	Updated expected diffs for new behavior (removed stopBuildOnErrors diff text)
internal/execute/build/orchestrator.go	Build-mode watcher now uses shared FileWatcher + directory computation
internal/execute/build/compilerHost.go	Added trackingvfs support to collect SeenFiles during compile
internal/execute/build/buildtask.go	Uses trackingvfs + watch-state update + package.json dependency checks
_extension/package.json	Added experimental setting typescript.native-preview.usePollingWatcher