When a tab's chrome.debugger session was torn down and re-established
(cross-process navigation, MV3 service-worker restart wiping the in-memory
maps, DevTools stealing the debugger), the extension minted a brand-new
monotonic `cb-tab-N` for the same tab. The daemon stays bound to the old id and
the relay consumes attach/detach events without telling it to rebind, so the
session was orphaned permanently → `stale sessionId / tab is gone`, and re-open
never recovered.
Derive the session id from the STABLE Chrome tabId (`cb-tab-<tabId>`) instead.
Any re-attach of the same tab now restores the SAME session the daemon already
holds, so eval/snapshot transparently follow the new page after a navigation.
Extension 0.4.3 → 0.4.4. Adds a relay unit test for the detach→reattach-same-
session recovery contract.