VS Code API Coverage Matrix

Authoritative map of every top-level vscode.* API surface and its implementation split across Sky (workbench renderer), Cocoon (extension-host Node sidecar), and Mountain (Rust backend). Drives the dual-track strategy:

• Track A - Stock-Node: Cocoon loads stock VS Code extHost*.ts sources unchanged; the workbench’s mainThread*.ts runs inside Sky (already the case - Sky ships the patched vs/workbench bundle). The ExtHostContext/MainContext RPC glue is provided by Cocoon’s shim alongside stock extHost code. This yields maximum compatibility from day one for any API the stock implementation handles in-process.
• Track B - Rust-native: Mountain owns the backend. Cocoon’s vscode shim sends gRPC to Mountain which does the work natively (filesystem, process, terminal, search, git). Faster and safer than bouncing through Node for I/O-heavy APIs.

The two tracks are not mutually exclusive. Most APIs live on Track A by default (stock compat guaranteed), and we promote individual operations to Track B when a measured benefit exists. The Cocoon <Namespace>Route.ts tier router documented in Cocoon/Source/Services/Handler/VscodeAPI/ROUTING.md decides per-call.

Legend

Status symbols:

• ✅ Working end-to-end (activation + feature render path confirmed)
• 🟡 Partial - RPC wired but UI render gap, or missing sub-method
• 🔴 Stubbed / dropped-on-floor - registration accepted, no effect
• ⚪ Not yet attempted
• 🟢 Pure-function lift (stateless, no RPC) already landed via Cocoon/.../VscodeAPI/StockLift.ts

Coverage summary (2026-06)

1. Top-level namespaces

vscode.commands

vscode.window - Editors

vscode.window - Surfaces (TreeView, StatusBar, Webview, Terminal)

vscode.workspace

vscode.languages

vscode.debug

vscode.tasks

vscode.scm

vscode.env

Extension secrets: context.secrets.get/store/delete are backed by encryption:encrypt / encryption:decrypt IPC (AES-256-GCM, machine-stable key derived as SHA-256 of the machine UUID). Handlers live in Element/Mountain/Source/IPC/WindServiceHandlers/Encryption/.

vscode.extensions

vscode.authentication

vscode.notebooks

vscode.tests

vscode.chat / vscode.lm

vscode.l10n

vscode.comments

2. Domain-grouped preferred-primary matrix

Grouped to highlight where Rust wins vs where Node-stock wins.

Rust-native primary (Track B wins)

High I/O, process, or syscall-bound operations where Node adds latency and the stock code ultimately bridges to the same native syscall anyway:

• File system - workspace.fs.*, scanner reads. Mountain owns File::* via tokio, gives us zero-copy, sandbox gating, and transparent scheme resolution. Stock extHostFileSystemConsumer.ts would just marshal JSON over IPC to do the same syscall.
• Find files / text search - workspace.findFiles / findTextInFiles. Mountain’s globset + walk is measured faster than Node’s glob package; migrating to ripgrep crate is the next perf tier.
• Terminal PTY - already Mountain-owned via portable-pty. Stock extHostTerminalService.ts is a shim that forwards to a native PTY regardless; Land cuts out the middle hop.
• Git subprocess - the built-in git extension’s $gitExec call pattern. Mountain spawns git as a child process and returns raw stdout.
• File watch - createFileSystemWatcher. Today a Stub; next tier is Mountain notify crate which avoids Node’s well-known fs.watch platform-quirk swamp.
• Native dialogs / clipboard / openExternal - Tauri already covers these. No Node alternative in an Electron-less build anyway.
• Process spawn for debug adapters / task exec - upcoming; Mountain child_process via tokio::process.

Node-stock primary (Track A wins)

State-heavy or coordination-heavy APIs where stock VS Code already handles nuance (revision history, undo merge, decoration overlay, language feature merge, cancellation token propagation) we’d have to re-implement. Lifting the stock file unchanged is cheaper than maintaining an original Rust backend:

• Command registry - extHostCommands.ts already does arg validation, contributed-command routing, cancellation. Sky calls the real ICommandService; Cocoon mirrors through stock.
• Language features - extHostLanguageFeatures.ts manages provider registries, merges results from multiple providers, caches. Rust rewrite would be months; the gRPC path just proxies which is cheap.
• Editor / document / selection - extHostDocuments.ts, extHostTextEditor.ts - source-of-truth for dirty state, encoding, EOL, versions. Must live in the extension host where edits originate.
• Configuration - extHostConfiguration.ts with scope resolution, override patterns, deprecation chains. Reuse stock.
• Messages / dialogs / quick-input - extHostMessageService.ts, extHostQuickOpen.ts. The UI is Sky’s, but the request/response serialisation is stock.
• Progress - extHostProgress.ts with cancellation, chained progress reporters. Stock.
• Secrets / storage / memento - extHostSecrets.ts, extHostStorage.ts
  • state shapes are VS Code-specific; stock lift.
• Authentication - complex session lifecycle, provider precedence. Stock.
• Debug / Tasks - protocol-heavy (DAP, task schema). Stock core + Mountain-owned process spawn for the transport.
• Webviews - extHostWebview.ts plus iframe-in-workbench UI. Stock end-to-end; Sky hosts the iframe.
• Notebooks - large surface, tightly coupled to workbench layout manager. Stock.
• Tree views - extHostTreeViews.ts handles visibility, selection, reveal, description updates. Stock + Sky render.

Hybrid (per-operation split)

• SCM - extHostSCM.ts stock for provider registration and resource-state updates, but git.createSourceControl needs a round trip to the workbench’s ISCMService (Sky direct) for the viewlet to render; the git extension’s $gitExec stays Mountain-native.
• Terminal shell integration - shell events via extHost, PTY via Mountain.
• FileSystemProvider - if an extension registers one, Cocoon forwards reads via gRPC to Mountain for disk ops; the provider interface itself lives in stock.
• Status bar - stock extHostStatusBar.ts manages entry lifecycle; Sky’s native IStatusbarService renders via __CEL_SERVICES__.Statusbar (just landed).

3. Track-A bring-up plan (full Stock-Node compat)

To get a stock extHost*.ts file running unchanged inside Cocoon, the following glue must exist (most already does):

1. ExtHostContext / MainContext RPC channels - bidirectional JSON-RPC between Cocoon and Sky. Today Cocoon↔Mountain is gRPC (Vine.proto), Sky↔Mountain is Tauri IPC. A third lane - Cocoon↔Sky direct - would let stock extHost*.ts talk to mainThread*.ts without Mountain as a middle hop. Candidates:
   • Mountain as relay (works today): Cocoon emits gRPC notification → Mountain re-emits as sky:// Tauri event → Sky’s mainThread shim receives. Extra hop, but no new transport. Good for low-rate registrations; skip for hot paths.
   • SharedWorker message port (future): Sky creates a MessageChannel, handshake via Mountain, then Cocoon↔Sky talk directly over the port. Requires Tauri’s worker support to allow SharedWorker in WKWebView, which today is blocked by CSP; tracked as a deferred item.
2. RPCProtocol instance in Cocoon - stock extHost.api.impl.ts calls rpc.getProxy(MainContext.MainThreadX) to get a proxy. Cocoon needs to supply a RPCProtocol that routes proxy method calls down the Cocoon↔Sky lane. Bespoke MountainClientService.ts in Cocoon is the current stand-in; lifting stock rpcProtocol.ts from src/vs/workbench/services/extensions/common/ is the next step.
3. Service identifier registration - stock MainContext / ExtHostContext registries (src/vs/workbench/api/common/extHost.protocol.ts) define one proxy identifier per mainThread and extHost class. Cocoon can import this file verbatim once RPCProtocol is in place.
4. IExtHostRpcService - the DI token stock extHost*.ts asks for. Cocoon’s mini-DI already exists (Services/Handler/*Service.ts) - add an extHostRpcService binding that returns our RPCProtocol.
5. mainThread*.ts loading in Sky - Sky already ships the vs/workbench/api/browser/mainThreadX.ts bundle. What’s missing is the instantiation at workbench startup; stock VS Code’s ExtensionService calls createExtensionHostManager which registers every mainThread. Sky needs to kick off that registration against Cocoon as the extension host.

Roadmap (concrete, in dependency order):

1. Lift rpcProtocol.ts into Cocoon → export from Cocoon/Source/Services/Handler/VscodeAPI/StockLift.ts.
2. Lift extHost.protocol.ts unchanged; expose ExtHostContext and MainContext as importable constants.
3. Add Cocoon↔Sky Mountain-relay lane: pair of gRPC notifications cocoonToSky(payload) + skyToCocoon(payload) that Mountain just forwards. Both sides marshal the stock MessageType enum.
4. Instantiate stock mainThread classes in Sky on cel:workbench-ready.
5. Start with low-risk namespaces: mainThreadCommands.ts first (command registry is the simplest), then mainThreadStatusBar.ts, then mainThreadMessageService.ts. Sky renders via the native workbench services as before.
6. Once the relay + stock-mainThread loop is green for commands, migrate the remaining namespaces namespace-by-namespace. Each migration is a net removal of Cocoon’s bespoke <Namespace>.ts shim in favour of import { ExtHostX } from '@codeeditorland/output/vs/workbench/api/common/extHostX.js'.

Current status (2026-06): The Mountain-relay lane (pattern 1) is implemented and in production. SharedWorker message port remains deferred pending Tauri WKWebView CSP support.

4. Track-B bring-up plan (Mountain-native acceleration)

For each domain where Rust is the preferred primary, the pattern is:

1. Add the gRPC method to Mountain/Proto/Vine.proto (the Vine submodule).
2. Implement the Rust handler under Mountain/Source/IPC/WindServiceHandlers/<Domain>/<Method>.rs - one file per method (per PascalCase naming convention).
3. In Cocoon’s <Namespace>Route.ts, add a Layer<N> tier that picks Mountain for that operation.
4. In Cocoon’s <Namespace>.ts shim, call MountainClient.sendRequest(method, args) behind the tier guard.
5. Update Architecture-Tiers.md manifest at build time so the dual-track dev-log tag reports which ops moved to Mountain.

Priority list (ranked by expected impact):

1. File watcher (notify crate) - today FileWatcher=Stub, so every extension that relies on watch events to rebuild / reload / re-analyze silently waits forever. Highest user-visible gap among the stubs.
2. Debug adapter spawn - Mountain spawns the adapter child process over DAP; Cocoon proxies DAP messages. Unblocks every debug extension.
3. Task execution - Mountain spawns the shell command, streams stdout/stderr through the terminal panel, tracks exit code.
4. Git subprocess - landed. Every $gitExec round-trip now routes to Mountain’s localGit:exec handler (HandleExec.rs) or the curated handler for clone/pull/checkout/revParse/fetch. Implemented in Batch 4 of the HANDOFF sequence.
5. Ripgrep-backed text search - swap globset walk for ripgrep crate’s grep_searcher. 10-30× speed-up on large repos.

5. Verification

After each namespace migrates:

• LAND_DEV_LOG=dual-track line confirms the route decision per op.
• PostHog land:dual-track:{shim,stock,mountain} marks record traffic by tier.
• Integration test: launch with LAND_DEV_LOG=short,provider-register, exercise the feature from the UI, grep for Activation failed (must be 0) and $<method> (no handler) (must be 0).

6. Gap register (highest-priority next items)

• 🟡 vscode.debug.* end-to-end - startDebugging, activeDebugSession, addBreakpoints/removeBreakpoints are all now partial (Cocoon shim + Sky Bridge wired); remaining gap is debug:start transport to a real DAP adapter process and DAP pipe/socket adapters in DebugProvider.rs.
• 🟡 vscode.tasks.executeTask - executeTask is now wired through Task.Execute Mountain round-trip with a live TaskExecution return and task.didStart / task.didEnd events; remaining gap is Mountain-side process spawn for shell tasks (PTY or tokio::process).
• 🔴 vscode.window.createWebviewPanel - blocks GitLens graph panel, Copilot chat, markdown-preview internals.
• 🟡 vscode.scm viewlet route into ISCMService - extensions register but UI stays empty (prior Investigation step 4 deferred).
• ✅ Tree-view renderer wiring (F1.1) - landed: extension-registered tree views now render via __CEL_SERVICES__.TreeViewByViewId(id).dataProvider attached on cel:tree-view:create. Supports refresh + dispose via the matching sky://tree-view/* channels, and full ITreeItem field fidelity (description / tooltip / resourceUri / contextValue / command).
• ✅ localGit channel - landed.
• ✅ Terminal shell integration (OSC 633) - onDidStartTerminalShellExecution, onDidEndTerminalShellExecution, and onDidExecuteTerminalCommand are fully wired end-to-end: Sky OSC 633 parser → localPty:shellExecution{Start,End} → Mountain fan-out → Cocoon $acceptTerminalShellExecution{Start,End} + $acceptExecutedTerminalCommand gRPC → Emitter events in Window namespace.