Enable inline history summarization and GPT-5.5 tool search

[bhavyaus]

Summary:

• Enable inline agent history summarization by default in Copilot configuration.
• Add GPT-5.5 model IDs to the Responses API tool search gate while keeping the existing experiment setting check.

[Copilot]

Pull request overview

Enables Copilot’s inline agent history summarization by default and expands the Responses API tool-search gating logic to recognize GPT‑5.5 model IDs (while still requiring the existing experiment/setting gate).

Changes:

• Flip the default for github.copilot.chat.agentHistorySummarizationInline to true (code + contributed setting).
• Update tool-search model ID gating to include GPT‑5.5 (and normalization for dot vs hyphen variants).
• Extend unit tests for modelSupportsToolSearch to cover GPT‑5.5 IDs.

Show a summary per file

File	Description
extensions/copilot/src/platform/endpoint/test/node/chatModelCapabilities.spec.ts	Adds GPT‑5.5 coverage to modelSupportsToolSearch tests.
extensions/copilot/src/platform/endpoint/common/chatModelCapabilities.ts	Extends Responses API tool-search model ID gating logic and normalization.
extensions/copilot/src/platform/configuration/common/configurationService.ts	Changes default for inline agent history summarization to enabled.
extensions/copilot/package.json	Updates the contributed configuration default for inline history summarization to true.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 2