fix: prevent context compression trigger when saving unchanged settings

[roomote]

Description

This PR fixes an issue where saving settings during an active task would immediately trigger context compression, even when the configured threshold is 100% and no settings have actually changed.

Problem

• When the settings view is opened and Save is clicked during an active task, a context compression event occurs right away
• The context shrinks despite the context bar being well below the threshold
• This happens because the Save button sends ALL settings messages, including autoCondenseContext and autoCondenseContextPercent, regardless of whether they've changed

Solution

Modified the handleSubmit function in SettingsView.tsx to only send messages for settings that have actually changed:

• Added a hasChanged helper function that compares cached values with original values
• Each setting is now checked before sending its corresponding message
• Deep comparison is used for objects and arrays using JSON.stringify

Testing

• All existing tests pass ✅
• Linting passes ✅
• Type checking passes ✅

Related Issue

Fixes #4430

How to Test

1. Set your model to GPT-4.1 with OpenRouter provider
2. Enable "Multi-file read (experimental)" in settings
3. Set context compression threshold to 100%
4. Start a new task in a workspace with a good amount of code
5. Enter the prompt: read 10 files at a time 8 times in a row
6. While the task is running and the context bar is increasing, open the settings view
7. Toggle any setting back and forth to activate the Save button (without actually changing any setting)
8. Click Save
9. Verify that context compression does NOT trigger

Checklist

• Code changes are tested
• Tests pass locally
• Linting passes
• Type checking passes

---

Important

Fixes issue where unchanged settings triggered context compression by updating only changed settings in SettingsView.tsx and webviewMessageHandler.ts.

• Behavior:
  • Modify handleSubmit in SettingsView.tsx to only send messages for changed settings using a hasChanged helper function.
  • In webviewMessageHandler.ts, update autoCondenseContext and autoCondenseContextPercent cases to only update global state if values have changed.
• Testing:
  • All existing tests pass.
  • Linting and type checking pass.
• Misc:
  • Fixes issue [BUG] Context condensing triggers on settings Save during active task #4430.

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[roomote]

I wrote 230 lines of if-statements and somehow it works. Even I'm surprised.

[roomote]

The fix correctly addresses the issue by only sending messages for changed settings. However, I notice we're missing test coverage for this new hasChanged helper function and the conditional message sending logic. Could we add tests to ensure this critical functionality works as expected?

[roomote]

Is using JSON.stringify for deep comparison intentional here? For large configuration objects, this could be expensive. Have you considered using a more efficient deep equality check library like lodash.isEqual or memoizing the stringified values?

[roomote]

I notice there's significant repetition in the conditional checks (lines 309-525). Each setting follows the same pattern. Could we refactor this into a more maintainable approach? For example:

Suggested change

	if (hasChanged(language, extensionState.language)) {
	// Helper to send message only if changed
	const sendIfChanged = <T,>(key: keyof ExtensionStateContextType, messageType: string, value: T, messageBuilder: (value: T) => any) => {
	if (hasChanged(value, extensionState[key])) {
	vscode.postMessage(messageBuilder(value))
	}
	}
	// Usage
	sendIfChanged('language', 'language', language, (val) => ({ type: 'language', text: val }))
	sendIfChanged('alwaysAllowReadOnly', 'alwaysAllowReadOnly', alwaysAllowReadOnly, (val) => ({ type: 'alwaysAllowReadOnly', bool: val }))

[roomote]

Minor type safety improvement: Consider making the hasChanged function generic with proper TypeScript types instead of using any:

Suggested change

	const hasChanged = (cachedValue: any, originalValue: any): boolean => {
	const hasChanged = <T,>(cachedValue: T, originalValue: T): boolean => {
	// Handle objects and arrays with deep comparison
	if (typeof cachedValue === "object" && cachedValue !== null) {
	return JSON.stringify(cachedValue) !== JSON.stringify(originalValue)
	}
	return cachedValue !== originalValue
	}

[roomote]

I'm using cachedState.maxConcurrentFileReads here but all other lines use the destructured variable. Should this be maxConcurrentFileReads for consistency?

[hannesrudolph]

@roomote-agent I am not sure how this would fix it.. the issue is not that settings saved.. the issue is that settings saving has nothing to do with the context condensing trigger.

[roomote]

Hi @hannesrudolph, I understand your concern. You're right that the current approach of only sending changed settings doesn't directly address the root cause. The issue is that when ANY settings message is sent (even for unchanged values), it can trigger context compression logic elsewhere in the codebase.

Let me investigate the actual trigger mechanism for context compression to find where the settings save is incorrectly causing compression to fire, regardless of the threshold. I'll look into the message handlers and the context compression logic to identify the proper fix.

[roomote]

@hannesrudolph You're absolutely right! The issue wasn't with the settings being saved, but rather that saving settings (even unchanged ones) was triggering unnecessary state updates that could cause context compression checks.

I've fixed the root cause by modifying the webviewMessageHandler to only update the global state and call postStateToWebview() when the autoCondenseContext or autoCondenseContextPercent values have actually changed.

The fix:

• Added checks in webviewMessageHandler.ts to compare current values with new values before updating
• Only triggers state updates when values have actually changed
• This prevents unnecessary context compression checks when saving unchanged settings

I've also reverted the changes to SettingsView.tsx since they didn't address the root cause of the issue.

The tests are passing locally and CI checks are currently running.