`gsd -p --model X "msg"` was silently overwriting defaultProvider/
defaultModel in settings.json. One-shot verification runs must use the
model for that invocation only.
Adds an AgentSessionConfig.persistModelChanges flag (default true so
interactive behavior is unchanged), forwards it through createAgentSession,
and sets it false in main.ts when !isInteractive and in src/cli.ts print
mode. The gsd wrapper also skips validateConfiguredModel when --model is
explicitly passed, so a CLI-provided model can't trigger a fallback repair
that writes the wrong default back.
Three settings.json write sinks audited: agent-session._applyModelChange
(gated on flag), model-selector.ts (interactive only, unreachable in
print), startup-model-validation (gated by !cliFlags.model in print).
Regression: 8 source-assertion tests in
agent-session-print-mode-persist.test.ts.
828c5edf62