fix(search): avoid hanging on custom FS schemes without a search provider (#260035)

[maruthang]

What

Search no longer hangs when the only workspace scheme is a custom file-system provider (e.g. memfs:/) that doesn't register a dedicated search provider.

Why

SearchService.searchWithProviders awaited waitForProvider on a deferred promise that would never resolve for extensions that register only an FS provider — the spinner stayed up forever. This also stalls Copilot agent-mode text searches on such workspaces.

How

When no search provider is registered for a scheme, also check fileService.hasProvider(scheme). If an FS provider is already present (extensions are awaited earlier via extensionService.whenInstalledExtensionsRegistered()), skip the scheme with a warning instead of waiting on a deferred promise that will never resolve. Normal file:// scheme behavior is unchanged because a search provider is always registered before file is queried.

Test plan

• Added src/vs/workbench/services/search/test/common/searchService.test.ts — builds a SearchService with a mocked TestFileService where hasProvider(memfs) === true, issues a memfs:/ text query, and asserts it completes (empty results) within 2s. Pre-fix this would time out.
• Manual repro: open the fsprovider-sample extension in VS Code, open the MemFS workspace, and run a text search — pre-fix the spinner hangs forever; post-fix the search completes immediately with a warning logged for the unsupported scheme.
• npm run compile-check-ts-native passes cleanly.

Fixes #260035

[Copilot]

Pull request overview

Fixes a hang in search when the workspace uses a custom file-system scheme (e.g. memfs:/) that has an IFileSystemProvider but no dedicated search provider. Previously SearchService.searchWithProviders would await waitForProvider(...) on a deferred promise that was never resolved, leaving the search spinner (and Copilot agent text searches) hanging forever.

Changes:

• In searchWithProviders, when no search provider exists for a scheme, also consider fileService.hasProvider(scheme) and skip the scheme (with a warning) instead of waiting indefinitely.
• Updated the warning message to distinguish the two skip reasons (another scheme has a provider vs. only an FS provider is registered).
• Added a new searchService.test.ts that asserts a memfs:/ text query completes (does not hang) when only an FS provider is registered.

Show a summary per file

File	Description
src/vs/workbench/services/search/common/searchService.ts	Skip schemes with only an FS provider registered to avoid awaiting a never-resolved deferred; refined warning message.
src/vs/workbench/services/search/test/common/searchService.test.ts	New unit test verifying textSearch returns promptly (empty results) for a scheme with only an FS provider.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 0