test(maestro): assert the agent session id survives recover()

The test named for recovery only read the sidecar back; nothing covered
the id reaching the recovered session, which is what a resume reads.

Also narrows RESTART.md's leniency claim: the custom Deserialize lives in
the client's own binary, so an older build still fails on Dormant.

docs/RESTART.md

@@ -83,9 +83,12 @@ resized, and neither watcher pass touches it. It is a record of what was
 running, and the only thing left to do with one is dismiss it, which removes
 the sidecar so the next recovery does not bring it back.
 
-`SessionStatus` is a wire type, so it deserializes leniently on both clients:
-a spelling this build does not know reads as `Dead` rather than failing the
-whole session. Clients render a dormant session as known-but-not-running —
+`SessionStatus` is a wire type, so from this build forward it deserializes
+leniently on both clients: a spelling the client does not know reads as `Dead`
+rather than failing the whole session. That leniency lives in the client's own
+binary, so it covers spellings added *after* this build, not this one — a CLI
+or TUI still running an older build fails to parse a `Dormant` session, and
+with it the whole session list, until it is upgraded. Clients render a dormant session as known-but-not-running —
 see `docs/SIDEBAR.md` for the card and `docs/COMMAND-BAR.md` for how it ranks.
 
 ## Timing