The morning a deprecation notice appeared, I checked versions before editing config
Claude Desktop and Cowork stop accepting older managed-configuration spellings on October 7. Here is how I sorted mine into what to fix now, what to fix after upgrading, and what changes meaning on its own.
The ~/.claude.json Rollback Is Fixed in v2.1.259. Putting Back What It Erased Is Still Your Job
Concurrent sessions used to silently roll back each other's ~/.claude.json changes. v2.1.259 fixed that, but nothing restores the trust settings and MCP servers you already lost. Here is how I find and rebuild them, with a small key-path diff script.
Once I passed a dozen MCP servers, I stopped trusting the startup list
Only some of the servers that say connection failed at startup are ones you can actually fix. Here is a probe that separates no-response, launch failure, and protocol rejection, measured across a 14-server fleet where sequential 22.03s became parallel 5.09s, and where trimming the deadline quietly turned healthy servers into failures.
Not Every Unreachable Connector Means the Same Thing in an Unattended Run
When an unattended task cannot reach a connector, the cause splits into three states: still connecting, unauthenticated, or genuinely absent. Each demands the opposite response. Here is the resolver that tells them apart.
The listen Stream Kept Reopening Against My Serverless MCP Server
No errors anywhere, yet connections to the MCP server kept piling up overnight. Here is what happens when a fixed platform timeout meets a resubscribe loop, reproduced in a few dozen lines.
The 400-Character Preview That Was Still Holding On to a Megabyte
Truncating tool output in your own MCP server does not free the original. Node's sliced strings keep the parent alive. Here is the measured 13-character boundary, which flattening tricks actually work, and a heap-snapshot audit script that counts the retained parents for you.
The MCP Server Connects Fine and Still Hands Back Zero Tools — Catching Silent Capability Drift with a Tool Manifest Diff
A missing credential does not break the MCP handshake. initialize succeeds, tools/list succeeds, and the array comes back empty. Here is the measured behaviour, and a preflight that locks the expected tool surface and fails closed before the agent ever starts.
The Line That Disappears at 100K: Measuring What Tool-Output Spill Actually Keeps
When agent tool output passes 100,000 characters, the full text spills to a file and the model sees only a head-truncated preview. Here are measured survival rates from a real repository, and the output envelope I built to push decision-relevant lines to the front.
Whose Environment Expands That Variable? Fingerprinting Your Effective Managed MCP Policy
Variable references in the Managed MCP allowlist and denylist now resolve from the startup environment and the managed-settings env block. I rebuilt both resolution orders locally to see where verdicts diverge, then wrote a preflight check that reduces the effective policy to a comparable fingerprint.
Rebuilding a Remote MCP Server That Never Needed Mcp-Session-Id
The MCP spec release candidate drops the session header. Here is how I audited my own remote server for session coupling and moved it to signed cursors, with measurements.
One Shared Managed Agent Definition, Overridden Per Session
A design for collapsing four near-identical Managed Agents into one base definition, using agent version pinning and session-local overrides — with a validated factory and the traps I hit along the way.
Resolving Tool Name Collisions When Bundling Multiple MCP Servers in the Claude Agent SDK
When the GitHub MCP and Linear MCP both expose create_issue, Sonnet 4.6 cannot tell them apart. This article covers the structure of MCP tool name collisions, a TypeScript reconciler implementation, and a measured correction: the schemaHash I originally published missed all five schema drifts I tested it against.