feat: add sparse checkout support for workspaces

[Ziinc]

Summary

This PR adds sparse checkout functionality to workspaces, allowing users to create workspaces that materialize only a subset of files matching specified patterns. This is useful for large monorepos where developers only need to work with specific directories.

Key Changes

Core Functionality

• Sparse pattern validation and application: Added parse_sparse_patterns() in jj.rs to validate user-supplied patterns and convert them to jj's RepoPathBuf format. Patterns are validated before any side effects occur.
• Workspace creation with sparse patterns: Extended create_workspace() to accept an optional sparse_patterns parameter that gets registered in jj's working-copy state via set_sparse_patterns().
• Pattern validation logic: Moved files outside sparse patterns are rejected upfront to prevent commits with invisible files. Empty pattern lists are normalized to None (full checkout).

Database and Metadata

• Database schema: Added sparse_patterns column to the workspaces table to persist patterns across sessions.
• Metadata parsing: Created parse_workspace_metadata() function in core/workspaces.rs to centralize metadata JSON parsing, handling sparse_patterns alongside existing title, description, and moved_files fields.
• Workspace struct: Updated local_db::Workspace to include sparse_patterns field.

Frontend Integration

• UI components: Added sparse paths input field to WorkspaceLeftPanel and UnifiedWorkspaceDialog.
• Metadata helpers: Created workspaceMetadata.ts with parseSparsePathsInput() and buildCreateMetadata() utilities to handle newline-separated sparse path input from users.
• API types: Extended Workspace interface to include optional sparse_patterns field.

CLI and Commands

• Command dispatch: Updated NAPI dispatch and Tauri command handlers to pass sparse patterns through the metadata JSON.
• CLI support: Added --sparse flag to the CLI workspace add command.

Testing

• Comprehensive test suite: Added core_workspaces_sparse_checkout_test.rs with 11 tests covering:
  • Basic sparse materialization
  • Full checkout behavior (None vs empty patterns)
  • Pattern validation and error handling
  • Single-file patterns
  • Moved files validation
  • Included copy files behavior
  • Stacked workspaces with sparse patterns
  • Database persistence
  • Snapshotting behavior (files outside patterns not tracked)
  • jj sparse list registration
• Integration tests: Added TypeScript integration test for sparse workspace creation.
• Unit tests: Added tests for metadata parsing utilities.

Implementation Details

• Validation timing: Sparse patterns are validated in parse_sparse_patterns() before workspace creation, ensuring no partial state is left behind on errors.
• Pattern matching: Patterns use jj's prefix matching semantics where src matches both the src file and everything under src/.
• Normalization: Patterns are normalized by stripping ./ prefix and trailing slashes, with duplicates removed.
• jj integration: Sparse patterns are set on the working copy while it's still empty, ensuring only matching paths are materialized during checkout.
• Backward compatibility: Existing code paths without sparse patterns continue to work unchanged; None and empty lists both result in full checkouts.
  https://claude.ai/code/session_01ARzJzBaQCPUpHgYJqdi1zF

[Ziinc]

test

[github-actions]

📸 App QA screenshots

Re-ran the flow whose spec this PR adds or modifies — 4 captures. Other specs in the library were not run.

⬇️ Download the screenshots

workspace-sparse-checkout

• workspace-sparse-checkout-01-home-full-file-list.png
  • The home repo view's file browser lists the full repository root: src, docs, and README.md.
• workspace-sparse-checkout-02-dialog-collapsed.png
  • The workspace creation dialog is open over the dashboard.
  • A collapsed "Advanced" toggle with a right-pointing chevron sits between the Description field and the Branch Name field.
  • No sparse paths textarea is visible.
• workspace-sparse-checkout-03-advanced-expanded-filled.png
  • The "Advanced" toggle is expanded (downward chevron) revealing the sparse paths textarea.
  • The Branch Name input contains "feat/sparse-demo".
  • The sparse paths textarea contains "src".
• workspace-sparse-checkout-04-workspace-sparse-file-list.png
  • The workspace header shows the feat/sparse-demo branch, meaning the sparse workspace was created and opened.
  • The workspace's file browser lists only src (plus .jj) — docs and README.md from capture 01 are absent.
  • No error toast or dialog is visible.

Each bullet under a capture is what the spec claims that image should show — open the PNG and check it.

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_{commit 5f552ba · workflow run — this comment is updated in place on each run.}