Log error for invalid chatContext icon format instead of silently ignoring

[Copilot]

Invalid icon formats in chatContext contributions were silently ignored, making debugging difficult. For example, "icon": "copilot" instead of "icon": "$(copilot)" would cause the contribution to disappear without explanation.

Changes

Added validation and error logging in chatContext.contribution.ts:

• Invalid format detection: Log descriptive error when ThemeIcon.fromString() fails to parse a provided icon
• Error message: Explains required format ($(iconId) or $(iconId~spin)) with example
• Defensive handling: Silently skip if icon property missing (schema violation edge case)

const icon = contribution.icon ? ThemeIcon.fromString(contribution.icon) : undefined;
if (!icon && contribution.icon) {
    ext.collector.error(localize('chatContextExtPoint.invalidIcon', 
        "Invalid icon format for chat context contribution '{0}'. Icon must be in the format '$(iconId)' or '$(iconId~spin)', e.g. '$(copilot)'.", 
        contribution.id));
    continue;
}

Errors surface in extension development logs where extension authors expect validation feedback.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Invalid 'icon' silently broke my contribution</issue_title>
<issue_description>Testing #280380

I initially had this

"chatContext": [{
      "id": "my-chat-context-provider",
      "displayName": "My Chat Context Provider",
      "icon": "copilot"
    }],

Because I forgot how the 'icon' should be formatted. I had to change it to $(copilot) in order for the entry to show up here:

That's ok but I was looking for errors in the Window output channel. If a contribution is invalid and being ignored we should log an error.</issue_description>

<agent_instructions>This is for the API proposal for contributed chat contex.</agent_instructions>

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

• Fixes Invalid 'icon' silently broke my contribution #280652

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[Copilot]

Pull request overview

Adds validation to chatContext extension contributions so invalid icon strings no longer fail silently and instead produce a descriptive error in extension logs, improving debuggability for extension authors.

Changes:

• Parse chatContext contribution icon using ThemeIcon.fromString()
• Log an error and skip the contribution when the icon string is present but unparsable
• Keep defensive skipping behavior for missing icon (schema-violation edge case)

[Copilot]

The truthy check (contribution.icon ? ... : undefined and later if (!icon && contribution.icon)) will silently skip some invalid icon values like "" or null (both falsy), which defeats the goal of logging invalid formats. Consider checking specifically for property absence (e.g., contribution.icon === undefined) and validating typeof contribution.icon === 'string' before parsing so empty/invalid values still produce the error log.

Suggested change

	const icon = contribution.icon ? ThemeIcon.fromString(contribution.icon) : undefined;
	if (!icon && contribution.icon) {
	let icon: ThemeIcon | undefined;
	if (contribution.icon === undefined) {
	// Icon is required by schema, but handle defensively below
	} else if (typeof contribution.icon === 'string') {
	icon = ThemeIcon.fromString(contribution.icon);
	if (!icon) {
	ext.collector.error(localize('chatContextExtPoint.invalidIcon', "Invalid icon format for chat context contribution '{0}'. Icon must be in the format '$(iconId)' or '$(iconId~spin)', e.g. '$(copilot)'.", contribution.id));
	continue;
	}
	} else {