Toggle line comments with Ctrl+/ in the editor

[henrylee1003]

The code editor had no way to comment lines out except typing # or // on each one by hand, which is what a candidate ends up doing while debugging in the Test step with the clock running. Ctrl+/ and Cmd+/ now toggle a line comment on the current line or on every line the selection touches.

Before, with three lines selected, the chord did nothing. After, a = 1 / b = 2 / c = 3 becomes # a = 1 / # b = 2 / # c = 3, and pressing it again restores the text and the selection. The marker is # in the Python tab and // in the others, goes in at the block's shallowest indentation, and skips blank lines. A block is uncommented only when every non-blank line in it is already a comment, so a block holding one commented line gains a level instead of losing that line's.

Two choices a reviewer may want to weigh. The chord is matched on event.key === "/" rather than event.code, because the key in that position types - on a German layout and Ctrl with it is the browser's zoom. And the shortcut is always on rather than a sixth editor option beside the ones from #252, since it changes nothing until it is pressed; I am glad to gate it if that is preferred.

The edit goes through applyEditorEdit, the same path Tab uses, so it is one input event, one code_update and one undo step. toggleLineComment is a pure function in web/editor.js and reads its marker from lineCommentFor in web/tokenizer.js, so the two cannot disagree; indentSelection is not touched.

Validation, on Windows 11 with Node 24:

• node --test tests/browser/editor.test.js: 57 pass, 0 fail (11 new cases).

• node --test tests/browser/comment-shortcut.test.js: 5 pass, in Chromium through Playwright.

• All of tests/browser/*.test.js, two files at a time: 1049 pass, 10 skipped, 6 fail. The six are outside this change: five fail only on Windows (four on a c: import path, one on an empty URL in face-detector.test.js), and disabled auto indentation retains parsed bracket highlighting fails intermittently here on a clean main as well.

• ESLint and Prettier clean on the changed files; the pre-commit and commit-msg hooks passed.

• Each new behavior was broken on purpose and the tests watched to fail: five mutations of toggleLineComment and isToggleCommentKeystroke, and four of the keydown branch (never taken, language fixed to Python, preventDefault dropped, value assigned instead of applyEditorEdit).

• A live interview, served by the latest release binary (codetrial 0.1.0 (6d556b7)) started with --web-dir pointing at this branch's web/: the chord commented and uncommented the selected lines in the editor.

Not run locally: ./scripts/test.sh as a whole, because this machine has no Rust toolchain, so the Rust lanes are left to CI. Running all of tests/browser/*.test.js in parallel here timed out in many files, mine included, and passed when the same files ran one at a time; I did not run a clean main for comparison. Nothing under src/ changed.

Before and after in that live session, cropped to the editor:

Closes #273

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Summary by cubic

Adds Ctrl+/ and Cmd+/ to toggle a line comment on the current line or on every line the selection touches, so candidates debugging during the Test step no longer have to type # or // by hand. The marker is # in the Python tab and // in the others, goes in at the block's shallowest indentation, skips blank lines, and a block is uncommented only when every non-blank line in it is already a comment. Each toggle is one input event, one code_update, and one undo step; a held chord toggles once instead of flipping with each repeat.

The shortcut is always on rather than an editor option, and it matches on the typed character rather than key position, so Ctrl with a key that types - on a German layout still works as the browser's zoom. Closes #273.

^{Written for commit 47e3458. Summary will update on new commits.}

[ColtenOuO]

LGTM.

[jserv]

Thank @henrylee1003 for contributing!