InspectLease, CleanupStaleLease, runActiveLeaseCheck, and statusAt now
use the PID-aware IsStale predicate. A dead local owner PID makes a lease
stale immediately; SessionStatus / list / info reflect this with no
display-code change.
Corrects three cmd-package session-display test fixtures that built
"active" leases with the local hostname but synthetic PIDs — now that
freshness is PID-aware, an active session must be owned by a live
process, so the fixtures use os.Getpid().
Add internal/session.SessionStatus(wsDir) that derives a display-only
view of the workspace session lease. Pure read of .ctask/session.json
with no tmux invocation, no PID liveness, no lock acquisition, and no
mutation of lease state.
States: none | active | stale. Mode defaults to "direct" when a
pre-v0.5.3 lease lacks the field. Malformed leases surface as stale
with a diagnostic so the present-but-broken case stays visible
instead of being silently classified as none.
Reused for ctask info and ctask list in subsequent commits. Lifecycle
code continues to use the existing primitives (ReadLease, IsFresh,
InspectLease).
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