Adopt message attachment URI protocol

[roblourens]

Adopts the Agent Host Protocol message attachment rename from path to uri in VS Code.

Summary:

• Updates generated Agent Host Protocol files to the synced AHP revision.
• Carries protocol attachment URIs through VS Code as serialized protocol uri values and internal URI objects.
• Keeps file-scheme filtering and working-directory rebasing for chat attachments.
• Converts internal attachment URIs to Copilot SDK path / filePath values at the SDK boundary.
• Adds focused tests for protocol-to-agent and agent-to-SDK attachment conversion.

Related protocol PR: https://github.com/microsoft/agent-host-protocol/pull/84

Validation:

• Core - Typecheck: 0 errors
• Core - Transpile: latest run 0 errors
• Focused attachment tests: 70 passed, 0 failed
• Hygiene: passed

(Written by Copilot)

[Copilot]

Pull request overview

Adopts the Agent Host Protocol attachment field rename from path → uri and threads attachment URIs through VS Code using serialized protocol URI strings and internal URI objects, converting back to Copilot SDK path/filePath at the boundary.

Changes:

• Update chat → agent-host protocol dispatch to emit MessageAttachment.uri (string) and keep file-scheme filtering + working-dir rebasing.
• Update node side effects to parse protocol attachment URI strings into URI objects before calling agents.
• Update Copilot SDK boundary to map internal URI attachments back to SDK path / filePath, with focused unit tests for both conversion directions.

Show a summary per file

File	Description
src/vs/workbench/contrib/chat/test/browser/agentSessions/agentHostChatContribution.test.ts	Updates expectations to assert attachment uri strings and refines a skip-case test for non-file URIs.
src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostSessionHandler.ts	Emits protocol MessageAttachment objects with uri strings (post-rebase) instead of filesystem path.
src/vs/platform/agentHost/test/node/mockAgent.ts	Extends mock agent to record optional attachments passed to sendMessage.
src/vs/platform/agentHost/test/node/copilotAgentSession.test.ts	Adds test ensuring internal URI attachments map to Copilot SDK path/filePath.
src/vs/platform/agentHost/test/node/agentSideEffects.test.ts	Adds coverage for parsing protocol attachment URI strings into URI objects (turn + queued messages).
src/vs/platform/agentHost/node/copilot/copilotAgentSession.ts	Converts internal URI attachments to Copilot SDK path/filePath fields at the SDK boundary.
src/vs/platform/agentHost/node/agentSideEffects.ts	Parses action.userMessage.attachments[].uri strings via URI.parse before calling the agent.
src/vs/platform/agentHost/common/state/protocol/version/registry.ts	Updates action version registry for newly synced protocol actions.
src/vs/platform/agentHost/common/state/protocol/state.ts	Syncs generated protocol types including MessageAttachment.uri and additional session fields from the newer AHP revision.
src/vs/platform/agentHost/common/state/protocol/reducers.ts	Adds reducers for newly synced protocol actions (activity/meta).
src/vs/platform/agentHost/common/state/protocol/actions.ts	Adds newly synced protocol actions/types and updates unions accordingly.
src/vs/platform/agentHost/common/state/protocol/action-origin.generated.ts	Regenerates action origin/unions and dispatchability map to include the new actions.
src/vs/platform/agentHost/common/state/protocol/.ahp-version	Bumps the pinned agent-host-protocol revision hash.
src/vs/platform/agentHost/common/agentService.ts	Updates IAgentAttachment to carry a URI instead of a filesystem path.

Copilot's findings

• Files reviewed: 14/14 changed files
• Comments generated: 0