fix: start with an empty workspace and require folder selection

[kbuffardi]

Problem

A fresh browser.cpp extension tab currently displays an unsaved file tab containing a Hello World program. Although toolbar compilation is already gated on workspace sources, the visible sample makes the editor appear ready to compile and run before the user has selected a workspace.

Decision

Open means Open Folder. It remains a workspace directory picker, not a standalone file picker.

A fresh tab and a user-selected Start new project state will have no open tabs, no active file, no filename, and an empty editor. Reopening a prior workspace is the only case that restores previously open tabs.

After a folder is chosen through Open, browser.cpp will show the Explorer and workspace terminal context but will not auto-open README.md or any other file. The user opens an existing file by selecting it in Explorer.

For New File with no workspace, browser.cpp will first request a workspace folder, then use the existing inline Explorer filename input to collect and validate a workspace-relative name. Once the folder has been selected, cancelling the filename input keeps that folder open; cancelling the directory picker leaves the existing empty state unchanged.

Implementation plan

1. Make the empty editor a first-class state in src/ui/editor.js, src/ui/toolbar.js, and src/ui/app.js.

   • Initialize Monaco with an empty value so Hello World never flashes during boot.
   • Revise resetToNewProject() to clear open tabs, active path, editor content, diagnostics, status filename, file handle, workspace/sidebar state, terminal workspace state, and transient build state together.
   • Do not create untitled:default for a fresh or Start new project state.

2. Preserve and clarify session restoration in src/ui/session-persistence.mjs.

   • First launch, a declined/failed session reload, and Start new project must all reach the identical no-file state.
   • A successfully reloaded workspace restores its saved tabs exactly as today, including a valid zero-open-tab session.
   • Update obsolete comments that describe a default main.cpp / DEFAULT_SOURCE tab, and keep abandoned workspaces from being re-persisted.

3. Make folder-first file flows explicit in src/ui/toolbar.js and src/ui/filesystem.js.

   • Open invokes the existing directory picker and renders the selected workspace without auto-opening README.md or another initial file.
   • New File with no workspace invokes the directory picker before the inline filename control; the submitted name continues through existing workspace-path validation and creates/opens one real workspace tab.
   • Preserve cancellation behavior: directory-picker cancellation changes nothing; filename cancellation after a successful folder selection leaves the chosen folder open and creates no tab.

4. Audit compile/run affordances for an empty state.

   • Toolbar buttons and shortcuts must remain unavailable with no real workspace source.
   • Terminal g++ without explicit source paths must fail clearly when there is no active real document/workspace source; it must never compile an implicit default or empty buffer.

5. Extend E2E coverage and register any new suite in the explicit test:e2e command in package.json.

   • Fresh startup and Start new project after declining reload: no tabs, no active path, blank editor/status, no Hello World, and disabled compile/run controls.
   • Restored workspace sessions: saved tabs restore; zero-open-tab sessions remain empty.
   • Open Folder: selection renders Explorer but opens no file, including when root README.md exists; cancellation preserves state.
   • New File: no-workspace folder-first flow, filename validation/submission, and both cancellation cases.
   • Toolbar, shortcut, and terminal compile behavior with no active real source.

Acceptance criteria

• A fresh extension tab shows no open file or Hello World content.
• Start new project has the same no-file state.
• Reopening a prior folder restores its saved tabs; a restored workspace may legitimately have zero open tabs.
• Open Folder asks for a workspace and does not auto-open a file.
• New File asks for a workspace when needed, then for a valid workspace-relative name, and opens only the created file.
• Empty-state compile/run paths cannot compile an implicit default buffer.

Verification

• npm run lint
• npm run build
• npm run test:e2e

[kbuffardi]

Implemented in PR #91.

The reviewed plan was applied as follows:

• Fresh and Start new project states now contain no open tab and no starter source.
• Open remains Open Folder and does not auto-open README.
• New File remains folder-first, then uses the existing workspace filename input.
• Empty-state Save creates and opens a real workspace file.

Validation passed:

• npm run test:e2e (190 tests)
• npm run lint
• npm run build