Fix terminal prompt redraws to always start on a new line

[kbuffardi]

Problem

The terminal can display redundant prompts on the same line, for example browser.cpp:~$ browser.cpp:~$ . This has been observed when the clear terminal button or shortcut redraws the prompt after one is already visible, and the same class of bug can occur anywhere a prompt is restored without first ensuring the cursor is at the start of a fresh line.

Desired behavior

Every newly displayed shell prompt should begin on its own terminal line. Prompt redraws should never concatenate with an existing prompt, partially typed command, compiler/runtime output, or informational message.

Proposed solution

Centralize prompt rendering in src/ui/terminal.js behind a newline-aware helper. The helper should track whether the terminal cursor/output is already at a fresh prompt position and insert CRLF before writing a new prompt whenever the previous terminal write did not end on a fresh line. Then route prompt-producing paths such as clearTerminal(), resetTerminalSession(), showInitialPrompt(), onCompileResult(), onRunResult(), command completion, idle Ctrl+C, and Ctrl+L through the same invariant.

Acceptance criteria

• Pressing the clear terminal button after the prompt is visible redraws exactly one prompt, and that prompt starts on a new line.
• Pressing Ctrl+K after the prompt is visible has the same behavior as the clear button.
• The terminal never renders adjacent prompt text like browser.cpp:~$ browser.cpp:~$ .
• Existing startup behavior remains intact: the initial prompt is not shown before compiler readiness and is only written once.
• Existing command, compile, run, stdin, Ctrl+C, Ctrl+L, and workspace reset prompt flows continue to restore prompts correctly.
• Node E2E tests cover prompt newline behavior and the full E2E suite, lint, and build pass.

[kbuffardi]

Plan revision — approved requirements

@kbuffardi confirmed: “yes to all questions. To 4, the prompt should sit at the top-left with no blank line.”

Decisions

• Clear button / Ctrl+K discards partially typed input and shows one fresh empty prompt.
• Ctrl+L preserves partially typed input after redraw.
• A prompt following compiler or program output that lacks a trailing newline must begin on the following line.
• After any clear operation, the prompt appears at the cleared screen’s top-left with no leading blank line.
• Shell clear remains in command history but is not visible after the terminal is cleared.

Revised implementation plan

1. Inventory every prompt-producing path in src/ui/terminal.js and classify whether it preserves or discards typed input.
2. Replace the raw prompt write with one prompt-rendering path that allows a prompt only on a prompt-safe line. Track whether visible output ended with CRLF through a small shared write wrapper, or use an equivalent testable state mechanism.
3. Add one clear-screen helper for clearTerminal(), Ctrl+L, shell clear, and resetTerminalSession(); it explicitly resets line/prompt state after term.clear().
4. Route all prompt redraws through the helper without scattering manual CRLF writes. Include startup, command completion, compile/run completion, stop/error paths, and toolbar clear.
5. Add focused Node E2E coverage for clearTerminal/Ctrl+K, Ctrl+L with and without input, shell clear, output without trailing newline, initial prompt idempotence, and compiler-readiness ordering. The assertions should detect visible adjacent prompts rather than only count writes.
6. Validate with npm run test:e2e, npm run lint, and npm run build.

Scope: reuse the existing xterm and terminal-test harnesses; do not add dependencies.

[kbuffardi]

Implementation is ready for review in PR #79: #79

Delivered the approved behavior: clear/Ctrl+K discards typed input and redraws one prompt at the top-left; Ctrl+L preserves typed input; and restored prompts follow newline-less output on a new line. The patch version is now 0.4.7.

Validated with npm run lint, npm run test:e2e (179 passing), npm run build, and npm run version:check.