feat: add autoExpandDiffs setting to auto-expand diffs in chat messages

[roomote-v0]

Related GitHub Issue

Closes: #10955

Description

This PR attempts to address Issue #10955. Feedback and guidance are welcome.

Adds a new boolean setting autoExpandDiffs (default: false) under Settings > UI. When enabled, file edit diffs in chat messages (e.g. "Roo wants to edit this file") are automatically expanded instead of requiring a click on the collapsed filename bar.

Implementation details:

• Types layer (packages/types): Added autoExpandDiffs to globalSettingsSchema and the ExtensionState Pick type so it flows through the state system.
• Context (ExtensionStateContext): Added default value (false) and hydration handling.
• ChatView: Added a useEffect that watches groupedMessages and auto-expands any diff tool messages (editedExistingFile, appliedDiff, newFileCreated, insertContent, searchAndReplace, batchDiffApproval) when the setting is enabled. Only new (untracked) messages are expanded to avoid fighting with manual user toggles.
• UISettings: Added a checkbox toggle for the new setting.
• SettingsView: Wired the setting through cachedState for the save/discard workflow.
• i18n: Added English translation strings.

The CodeAccordion component already enforces a max-h-[300px] (300px) limit with overflow-y: auto, so auto-expanded diffs will not take over the chat view -- anything taller than 300px gets a scrollbar.

Test Procedure

• All existing UISettings tests updated and passing (4/4).
• SettingsView change-detection and unsaved-changes tests updated and passing (3 passed, 5 skipped -- skipped tests are pre-existing).
• All lint checks pass across the monorepo.
• All type checks pass across the monorepo.

Manual testing steps:

1. Open Settings > UI tab
2. Enable "Auto-expand diffs in chat messages"
3. Save settings
4. Start a task that edits files
5. Observe that diff blocks are automatically expanded in the chat

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue.
• Scope: My changes are focused on the linked issue.
• Self-Review: I have performed a thorough self-review of my code.
• Testing: Updated tests have been added to cover my changes.
• Documentation Impact: No documentation updates needed.
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Documentation Updates

No documentation updates needed. The setting is exposed in Settings > UI with a clear label and description.

[roomote-v0]

Rooviewer   See task

Reviewed. The settings plumbing, types, UI toggle, and i18n look correct. Found 2 issues in the auto-expand useEffect in ChatView.tsx:

• expandedRows in the dependency array causes unnecessary re-executions (every user expand/collapse re-iterates all messages with JSON.parse) and a double-run cycle on auto-expand. Use the functional updater of setExpandedRows and drop expandedRows from deps.
• Auto-expansion triggers the existing expansion-tracking effect (lines 509-529) which disables stickyFollowRef (auto-scroll). During an active task, each new diff auto-expand stops the chat from scrolling to new messages.

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}

[roomote-v0]

Including expandedRows in the dependency array here means this effect re-runs on every expansion/collapse (user or auto), iterating all modifiedMessages and JSON.parse-ing each one. It also causes a double execution when it auto-expands: the setExpandedRows call updates expandedRows, which re-triggers the effect (the second run is a no-op but still wasteful). You can fix both problems by moving the logic into the functional updater of setExpandedRows and dropping expandedRows from deps:

Suggested change

	useEffect(() => {
	if (!autoExpandDiffs) {
	return
	}
	const newExpansions: Record<number, boolean> = {}
	for (const msg of modifiedMessages) {
	// Skip messages already tracked in expandedRows
	if (expandedRows[msg.ts] !== undefined) {
	continue
	}
	// Check if this message contains a diff tool
	if (msg.text) {
	try {
	const tool = JSON.parse(msg.text)
	if (tool.tool && DIFF_TOOL_TYPES.has(tool.tool)) {
	newExpansions[msg.ts] = true
	}
	} catch {
	// Not valid JSON, skip
	}
	}
	}
	if (Object.keys(newExpansions).length > 0) {
	setExpandedRows((prev) => ({ ...prev, ...newExpansions }))
	}
	}, [modifiedMessages, autoExpandDiffs, expandedRows, DIFF_TOOL_TYPES])
	useEffect(() => {
	if (!autoExpandDiffs) {
	return
	}
	setExpandedRows((prev) => {
	const newExpansions: Record<number, boolean> = {}
	for (const msg of modifiedMessages) {
	if (prev[msg.ts] !== undefined) {
	continue
	}
	if (msg.text) {
	try {
	const tool = JSON.parse(msg.text)
	if (tool.tool && DIFF_TOOL_TYPES.has(tool.tool)) {
	newExpansions[msg.ts] = true
	}
	} catch {
	// Not valid JSON, skip
	}
	}
	}
	if (Object.keys(newExpansions).length > 0) {
	return { ...prev, ...newExpansions }
	}
	return prev
	})
	}, [modifiedMessages, autoExpandDiffs, DIFF_TOOL_TYPES])

_{Fix it with Roo Code or mention @roomote and request a fix.}

[roomote-v0]

When this effect auto-expands diffs via setExpandedRows, the existing effect at lines 509-529 will detect those transitions (from undefined to true) and set stickyFollowRef.current = false, disabling auto-scroll. It cannot distinguish between user-initiated and programmatic expansions. During an active task with autoExpandDiffs enabled, each new diff message gets auto-expanded, triggers that detection, and disables auto-scroll -- the user has to manually scroll to see subsequent messages, which undermines the purpose of this feature. Consider guarding against this by setting a ref flag (e.g. isAutoExpandingRef.current = true) before calling setExpandedRows here, and checking it in the expansion-tracking effect to skip the sticky-follow disable.

_{Fix it with Roo Code or mention @roomote and request a fix.}