Skip auto model router API call for cached inline chat

[Copilot]

The auto model router adds ~200ms latency to inline chat due to the classification API call. This change optimizes inline chat by skipping the router API call when a cached model selection already exists, while still participating in automodel routing.

Changes

Modified AutomodeService._resolveWithRouterModel() to skip router API fetch for inline chat when cache exists:

// For inline chat (ChatLocation.Editor), skip router fetching if there's already a cached entry
// to avoid 200ms latency penalty.
const prompt = chatRequest?.prompt?.trim();
const isInlineChat = location === ChatLocation.Editor;
const shouldRoute = prompt?.length && (!entry || entry.lastRoutedPrompt !== prompt) && !(isInlineChat && entry);

Behavior:

• First inline chat request: Routes normally using the router API to select the best model
• Subsequent inline chat requests: Reuses the cached model selection, avoiding the 200ms API call
• Other locations (Panel, Terminal, etc.): Continue to use router on every request as before

This approach allows inline chat to benefit from smart model routing while avoiding latency penalties on repeated requests.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Auto model router should not be used in inline chat</issue_title>
<issue_description>I believe that the auto model router is being used for all Auto usage today (when enabled).
We should make sure to not use the router for inline chat.
Reason:
a) Inline chat needs to be fast, and we do not want to pay the 200ms penalty
b) We always resolve to fast models in Inline Chat ourselves, thus the classifiation might not be needed at all

cc @jrieken @eleanorjboyd </issue_description>

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

• Fixes Auto model router should not be used in inline chat vscode#289145

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[Copilot]

Pull request overview

Optimizes Auto mode routing decisions to reduce latency for inline chat by avoiding router-classification calls under certain conditions.

Changes:

• Restricts router-based model selection to panel chat requests (other locations fall back to non-router behavior).
• Adds a new Vitest suite covering router usage (panel vs. inline/terminal/no-config).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/platform/endpoint/node/automodeService.ts	Gates router-based resolution behind a “panel chat only” check.
src/platform/endpoint/node/test/automodeService.spec.ts	Adds tests asserting router fetch usage/non-usage across chat locations and config states.