Harden terminal scrollback settings sync

[gedeagas]

Fixes review feedback from #114 by defensively parsing terminalScrollback in settings:sync before
updating mainSettings.

Validation:

• npm run typecheck
• npm test -- src/main/services/ptyDaemon/tests/protocol.test.ts src/main/services/ptyDaemon/tests/
  sessionHost.test.ts
• git diff --check origin/main..HEAD

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[gemini-code-assist]

Code Review

This pull request updates the IPC handler for settings synchronization in src/main/ipc.ts to handle and parse the terminalScrollback setting more robustly when it is passed as a string or null. The reviewer identified potential robustness issues: first, using the in operator on values without verifying it is a non-null object could cause a TypeError and crash the process; second, using Number() directly on untrusted input can lead to unexpected numeric conversions (such as booleans or arrays being parsed as valid numbers). A code suggestion was provided to safely check the object type and strictly parse only numbers and non-empty strings.

[gemini-code-assist]

Robustness & Defensive Parsing Issues

1. TypeError / Crash Prevention: Since values is received over IPC, it is untrusted input and could potentially be null, undefined, or a primitive. Using the in operator on a non-object (e.g., 'terminalScrollback' in values) will throw a TypeError and crash the IPC handler/main process. We should guard this check by verifying that values is a non-null object.

2. Strict Numeric Parsing: Using Number(rawScrollback) directly on non-numeric types can lead to unexpected results (e.g., Number(true) is 1, Number([]) is 0), which would then be clamped to 100 and saved as a valid scrollback setting. We should restrict parsing to actual numbers or non-empty strings.

    if (values && typeof values === 'object' && 'terminalScrollback' in values) {
      const rawScrollback = values.terminalScrollback as unknown
      let parsedScrollback = NaN
      if (typeof rawScrollback === 'number') {
        parsedScrollback = rawScrollback
      } else if (typeof rawScrollback === 'string' && rawScrollback.trim() !== '') {
        parsedScrollback = Number(rawScrollback)
      }
      if (Number.isFinite(parsedScrollback)) {
        values.terminalScrollback = clampTerminalScrollbackLines(parsedScrollback)
      } else {
        delete values.terminalScrollback
      }