Don't save debugger completion history for evaluations that return errors

[Copilot]

Debug Console history was polluted with incomplete/invalid expressions that failed evaluation. Typing myVar and pressing Enter before autocomplete finishes would add myVar to history even though it returned an error, pushing the correct myVariable down in suggestions.

Changes

Modified evaluation flow to track and propagate success status:

• ReplModel.addReplExpression(): Returns Promise<boolean> instead of Promise<void>, capturing the result from evaluateExpression()
• IDebugSession.addReplExpression(): Interface updated to return boolean
• Repl.acceptReplInput() / sendReplInput(): Made async, conditionally add to history only on success

const success = await session.addReplExpression(stackFrame, input);
if (success) {
    this.history.add(input);
}

Tests

• Added sendErrorResponse() to MockDebugAdapter for error simulation
• Test coverage for both successful (returns true) and failed (returns false) evaluations

Original prompt

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This section details on the original issue you should resolve

<issue_title>Don't save debugger completion history for evaluations that return errors</issue_title>
<issue_description>By default, completion in the Debug Console requires pressing <tab> to complete. Because I'm used to pressing <enter> I often send incomplete/invalid expressions. However these are still recorded to the history and then show in future invocations (which means the "top" entry is not the complete variable name that I want, but a previous mistyping):

I think it would be better if expressions are only recorded to the history if they evaluate successfully and do not return an error ("success":false).</issue_description>

Comments on the Issue (you are @copilot in this section)

@roblourens You might like `debug.console.acceptSuggestionOnEnter`

• Fixes Don't save debugger completion history for evaluations that return errors #278115

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