chat: Suppress missing Agent Host file read logs

[roblourens]

This suppresses expected Agent Host protocol error logs for missing file reads while preserving error propagation and warnings for unexpected failures.

What changed:

• Skip protocol-client request-failed warnings for NotFound responses from file resource reads.
• Skip protocol-server request-failed logs for the same missing file-read case.
• Keep warnings for synthetic resource reads (for example session-db/git-blob), non-read NotFound errors, and non-missing read failures.
• Map AgentService resourceRead failures more precisely so only actual missing files become NotFound.
• Add focused coverage for client, server, and AgentService error mapping behavior.

Validation:

• npm run typecheck-client
• npm run gulp compile-client
• ./scripts/test.sh --run src/vs/platform/agentHost/test/electron-browser/remoteAgentHostProtocolClient.test.ts --run src/vs/platform/agentHost/test/node/agentService.test.ts --run src/vs/platform/agentHost/test/node/protocolServerHandler.test.ts --grep "RemoteAgentHostProtocolClient|AgentService.*resourceRead|resourceRead"
• node --experimental-strip-types build/hygiene.ts src/vs/platform/agentHost/browser/remoteAgentHostProtocolClient.ts src/vs/platform/agentHost/test/electron-browser/remoteAgentHostProtocolClient.test.ts src/vs/platform/agentHost/node/agentService.ts src/vs/platform/agentHost/test/node/agentService.test.ts src/vs/platform/agentHost/node/protocolServerHandler.ts src/vs/platform/agentHost/test/node/protocolServerHandler.test.ts

(Written by Copilot)

[Copilot]

Pull request overview

This PR reduces log noise in the Agent Host protocol stack by suppressing expected NotFound warnings/errors for missing file resourceRead requests, while keeping error propagation and preserving logging for other NotFound cases (e.g. synthetic schemes like session-db:) and unexpected failures. It also refines AgentService.resourceRead error mapping so only actual missing files become NotFound, and adds targeted unit coverage for these behaviors.

Changes:

• Suppress protocol-client warnings for resourceRead NotFound responses when the requested URI is a file: resource.
• Suppress protocol-server error logs for the same expected missing-file resourceRead case.
• Refine AgentService.resourceRead error mapping (missing vs permission vs other failures) and add focused tests across client/server/service.

Show a summary per file

File	Description
src/vs/platform/agentHost/browser/remoteAgentHostProtocolClient.ts	Tracks per-request suppression metadata to avoid warning logs for missing file: reads while still surfacing the error to callers.
src/vs/platform/agentHost/node/protocolServerHandler.ts	Adds server-side filtering to avoid error logging for expected missing file: reads that return NotFound.
src/vs/platform/agentHost/node/agentService.ts	Improves resourceRead error mapping so only true missing files map to NotFound (and permission issues map to PermissionDenied).
src/vs/platform/agentHost/test/electron-browser/remoteAgentHostProtocolClient.test.ts	Adds coverage ensuring only missing file: reads suppress warnings (other NotFound cases still warn).
src/vs/platform/agentHost/test/node/agentService.test.ts	Adds coverage for AgentService.resourceRead error mapping (missing vs non-missing failures).
src/vs/platform/agentHost/test/node/protocolServerHandler.test.ts	Adds coverage ensuring the server does not log for missing file: reads but still logs for other missing-resource reads.

Copilot's findings

• Files reviewed: 6/6 changed files
• Comments generated: 2