Enable tool search and prefer-long-context by default

[Bhavya U (bhavyaus)]

Flips the defaults for two settings that have been baking behind an opt-in flag:

• chat.agentHost.copilot.toolSearch.enabled → true
• github.copilot.chat.preferLongContext.enabled → true

Why the diff touches more than two lines

Each setting's default lives in more than one place, and the pairs have to stay in sync:

Tool search

• chat.shared.contribution.ts — the user-facing workbench setting registration.
• copilotCliConfig.ts — the agent-host schema default the renderer forwards the value into.

Prefer long context

• extensions/copilot/package.json — the contributed setting default.
• configurationService.ts — ConfigKey.PreferLongContext. The extension throws a BugIndicatingError at load time if the code default drifts from package.json, so these two must change together.
• agentHostSchema.ts — the forwarded preferLongContextEnabled root-config default, plus its description, which stated false was the default.

Note on schema defaults

getRootValue returns undefined for unset keys rather than falling back to the schema default, so the effective defaults come from the VS Code / extension setting registrations that the renderer forwards on startup. The default fields in the agent-host schemas are advertised metadata and were updated to match so the two don't disagree.

Validation

• vitest on contextSizeOverride.spec.ts and chatSessionInitializer.spec.ts — 38 passed. This also exercises the package.json ↔ code default-consistency assertion.
• tsc --noEmit -p src/tsconfig.json — no new errors (two pre-existing failures in copilotAgentSession.ts / copilotSystemNotification.ts from local SDK type drift are untouched by this change).

[Copilot]

Pull request overview

Enables tool search and long-context preference by default across VS Code, Copilot, and agent-host schemas.

Changes:

• Enables tool search by default.
• Enables free long-context windows by default.
• Aligns forwarded schema metadata and descriptions.

Show a summary per file

File	Description
chat.shared.contribution.ts	Enables the workbench tool-search setting.
copilotCliConfig.ts	Updates agent-host tool-search schema metadata.
agentHostSchema.ts	Updates long-context schema default and description.
configurationService.ts	Changes the Copilot code default.
languageModelAccess.ts	Removes outdated default documentation.
package.json	Changes the contributed long-context default.

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 1
• Review effort level: Balanced