feat: durable command lifecycle logging in the executor (command/run + command/done)

CommandService.execute appends the log-only pair around every resolved
handler — run before invocation, done at settlement, including thrown and
aborted handlers (kind:'error'); admission misses log nothing. commandId is
minted monotonically per instance; per-session appends serialize through a
tail queue over SessionStore.appendOutOfBand (zero-step wrap on an idle log,
direct join inside an open turn). The invariant companion now asserts the
pairing relation (unique run ids; a done requires a prior in-log run).
CommandSource is a minimal merge-extensible map (user variant only).
Dependent benches mount SessionStore; TUI/e2e snapshots re-recorded for the
executor's durable-append timing and the /status event counts.

packages/ui/commands/package.json

@@ -30,6 +30,7 @@
     "@deepseek-ai/dsh-agent": "^0.0.1",
     "@deepseek-ai/dsh-invariants": "^0.0.1",
     "@deepseek-ai/dsh-scope": "^0.0.1",
+    "@deepseek-ai/dsh-session": "^0.0.1",
     "cordis": "^4.0.0-rc.7"
   },
   "devDependencies": {