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Sweep 28 Aug 2026 · 00:00Z Build v2.1.250 478 read Stable v2.1.236 Latest v2.1.250 Next v2.1.250 Feeds RSS JSON llms.txt

DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

Reference / Feature flags

tengu_mcp_server_connection_failed

A Claude Code feature flag, read out of the shipped bundle. No mined inventory carries it: everything below comes from what this site has written about it.

What it is

MCP debug output now shows which protocol version and path a server connection used.

Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.221.

Presence across releases

The miner has never read a build containing this name. It is here because a changelog entry of ours names it, which is evidence that it existed and not evidence of which releases carried it. The inventory starts at v2.1.138 and everything older than that was never mined.

Gate readings

No release here has a gate table behind it for this flag. Most published releases have none at all: the readings exist only for versions the pipeline captured flag state on.

Changelog entries naming it

  1. v2.1.248MCP connection-failure telemetry records where the auth header came from

    MCP connection failure reports now note when auth headers came from a credential helper.

    gate cited by this entry

  2. v2.1.224MCP events forwarded to Datadog, with identifying fields removed and a per-server cap

    MCP events are forwarded for logging with identifying fields stripped, and skipped entirely if analytics are off.

    gate cited by this entry

  3. v2.1.224MCP OAuth failures name the specific issuer mismatch

    MCP OAuth failures now tell you it was an issuer mismatch instead of a generic error.

    gate cited by this entry

  4. v2.1.222Dedicated error when claude.ai rejects a session bearer token

    If claude.ai rejects your session token, you now get a clear message telling you to run /login instead of endless retries.

    gate cited by this entry

  5. v2.1.221Connection telemetry gains negotiation and protocol fields

    MCP debug output now shows which protocol version and path a server connection used.

    gate cited by this entry

  6. v2.1.221Failure telemetry errorCode is now normalized against a fixed allowlist

    MCP connection failure reporting now uses a fixed set of error codes instead of raw values.

    gate cited by this entry

  7. v2.1.221MCP connection-failure telemetry records negotiation outcome

    Failed MCP connections now record how the handshake was negotiated and whether it fell back.

    gate cited by this entry

  8. v2.1.221MCP connection-failure telemetry normalizes the error code

    MCP failure codes are now cleaned up before reporting, so odd server values don't leak through.

    gate cited by this entry

Documentation pages

None of Anthropic's documentation pages this site has a copy of carries this name.

Names beside it

Every feature flag in the inventory starting tengu_mcp_server_connection, up to twelve of them.

tengu_mcp_server_connection_succeededMCP debug output now shows which protocol version and path a server connection used. never mined

Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the feature flag does. All feature flags.