GitHub connector shows "Connected" but exposes no tools — works on one machine, not another, same account

Environment

• Claude for Windows desktop app
• Same Anthropic account, two different machines

Machine A (working): "mo" — Claude for Windows 1.24012.9 (03c61d)
Machine B (broken): "kiva" — Claude for Windows 1.25927.0 (003700)

What's happening
On Machine B, Customize > Connectors shows GitHub as "Connected" — same as Machine A. But in chat sessions on Machine B, no github: tools are available at all. Tool calls either fail to resolve ("tool not found") or return a generic execution error, even against a completely unrelated public repository (not a private-repo permissions issue).

On Machine A, the identical account/connector works normally — full GitHub tool access, correct results.

Confirmed not an authorization issue
Checked github.com/settings/installations directly — the Claude GitHub App is installed and correctly scoped. The problem is client-side, not a missing grant.

Additional note
Within a single session on the broken side, behavior was inconsistent across attempts — at one point the same tools were present but calls failed generically, at another point they weren't resolvable at all without going through tool_search first. This may be the same underlying bug as #61682, #23775, #29415, and #58172, which describe the same "Connected but zero/broken tools" symptom in Cowork specifically — possibly the same root cause surfacing in desktop chat mode too, not just Cowork.

Screenshots
Will attach side-by-side "About Claude" screenshots showing both version numbers directly as a follow-up comment.