PreModelSwitch: Claude Code Can Now Veto a Model Change
Claude Code 2.1.251 adds PreModelSwitch and PostModelSwitch hook events. The matcher fires on the canonical name of the model you are switching to, and exit code 2 cancels the switch.
Tag: ai-agents
191 posts · Page 3 of 20
Stateful vs Stateless MCP Servers: What Actually Breaks When the Session Goes Away
Protocol revision 2026-07-28 deleted Mcp-Session-Id, the initialize handshake, resources/subscribe, ping, logging/setLevel and SSE resumability. An automated survey of 1000 open source MCP servers found 90% reference the session ID nowhere. Here is what the other 10% has to rewrite, with verified code on @modelcontextprotocol/server 2.0.0.
Claude Code 2.1.251 Closes Four Ways Around the Permission Check
A symlink swapped after the check, deny rules that stopped applying through a symlinked search path, a marketplace command pointing outside its plugin, and a workflow script read before approval. Four fixes in one release, all the same bug.
Fix: An MCP Server Never Starts Because an Enterprise Allowlist Blocks Its Command or URL
A server that vanished from /mcp with no error is almost always an allowlist. Run claude mcp add on the same server: the add path prints the reason the load path swallows.
Fix: MCP9004, MCP9005 and MCP9006 warnings after upgrading the MCP C# SDK to 2.0
MCP9005 is advisory, but MCP9004 crashes at startup and stateless mode makes SampleAsync throw. Here is what each diagnostic means and how to fix it properly.
Claude Code 2.1.238 Lets a Plugin Marketplace Mint Its Own Auth Headers
A headersHelper field on url marketplaces and catalog entries runs a local command that prints HTTP headers, so an internal plugin catalog behind S3 or an artifact repo can authenticate with a short-lived token. Here is the schema, the consent prompt, and the header names Claude Code drops.
Fix: Unsupported protocol version between an MCP client and server (2025-11-25 vs 2026-07-28)
MCP error -32022 means your client opened at 2025-11-25 but the server only serves 2026-07-28. Make one side dual-era instead of pinning a version.
How to Cut Cursor Cloud Agent Startup Time With Prebuilt Builds
Cursor shipped Builds for Cloud Agents on August 13, 2026: a bootable filesystem snapshot of an already prepared machine. Cursor reports 3x faster time to first token. The lever you control is the install vs start split in .cursor/environment.json.
How to Serve Agent Skills from an MCP Server in .NET with UseMcpSkills
Stop shipping SKILL.md folders inside every agent deployment. Serve them from an MCP server and pull them with UseMcpSkills on Microsoft.Agents.AI.Mcp 1.18. Includes the exact skill://index.json shape, a working C# server, the wire trace, and the SEP-2640 drift that will bite you.
How to Set the Reasoning Level for a GitHub Copilot Cloud Agent Per Task
Since August 3, 2026 you can pick a reasoning level next to the model when you start a Copilot cloud agent task. The Agent Tasks REST API has no equivalent parameter, so scripted dispatch cannot set it. Here is where the control exists, which levels each model exposes, what lands on the wire, and how to pin a default instead.