Implement project-based testing architecture for multi-project workspaces

[eleanorjboyd]

Adds infrastructure to support multiple Python projects (each with distinct Python executables and test configurations) within a single VS Code workspace. Currently behind a feature flag (useProjectBasedTesting = false) for safe deployment.

Core Infrastructure

• ProjectAdapter interface: Encapsulates project identity, Python environment, test adapters, and discovery state
• Project-scoped test IDs: Format {projectId}::{testPath} prevents ID collisions between projects
• Utility functions: Project ID generation via hash, nested project detection, ID scoping/parsing
• WorkspaceDiscoveryState: Temporary state for overlap detection and ownership resolution during discovery

Result Resolver Updates

• Added optional projectId parameter to PythonResultResolver constructor
• When present, prefixes all test IDs with project scope; when absent, uses legacy IDs (backward compatible)
• Updated populateTestTree() and TestDiscoveryHandler to propagate project scoping

Project Discovery Integration

• discoverWorkspaceProjects(): Queries Python Environment API for projects, filters to workspace, creates ProjectAdapter instances
• createProjectAdapter(): Resolves Python environment, creates project-scoped resolver and provider-specific adapters
• createDefaultProject(): Fallback that mimics single-workspace behavior using workspace interpreter
• State tracking maps:
  • workspaceProjects: Project registry by workspace URI
  • vsIdToProject: O(1) test-to-project lookup for execution
  • fileUriToProject: File-to-project mapping for file watching
  • projectToVsIds: Project-to-tests mapping for cleanup

Activation Flow

public async activate(): Promise<void> {
    if (this.useProjectBasedTesting) {
        // New: Discover projects via Python Environment API
        const projects = await this.discoverWorkspaceProjects(workspace.uri);
        this.workspaceProjects.set(workspace.uri, projectsMap);
    } else {
        // Legacy: Single WorkspaceTestAdapter per workspace
        this.activateLegacyWorkspace(workspace);
    }
}

Graceful degradation: Any failure in project discovery automatically falls back to legacy single-workspace mode. All new code paths are disabled by default until Phases 3-4 (discovery with overlap resolution, test execution) are implemented.

Files Changed

New:

• testController/common/projectAdapter.ts - Type definitions
• testController/common/projectUtils.ts - Utilities

Modified:

• testController/controller.ts - Project discovery and state management
• testController/common/resultResolver.ts - Project scoping support
• testController/common/testDiscoveryHandler.ts - Scoped error nodes
• testController/common/utils.ts - Scoped test ID creation