[Bug] subagent model selection (list_subagent_models, provider/model) silently missing in resumed/imported sessions and their children

[Clemens66666]

Environment: DSH Desktop 0.9.2 on Windows 11, @deepseek-ai/dsh-tool-subagent 0.1.5-rc.2, and settings.yaml with subagent-model-selection.enabled: true plus a non-empty allowedModels list.

Symptom: In some sessions, subagent has no provider/model parameters and list_subagent_models is not registered. The subagent-model-selection setting is ignored, and no error or hint appears. In other sessions on the same machine both are present.

We scanned 42 local session logs that use the dsh tools (through the dsh-oh-my-claude MCP bridge and natively). 20 of them have no subagent/model-selection-policy event.

Cause (dsh-tool-subagent/lib/index.js, selectForSession, ~L588-601): the policy is read from settings only for a fresh session:

const freshSession = target.firstLiveSeq === 0 && target.eventAt(SessionSeq(0))?.type !== "session/end-seed";
let allowedModels = subagentModelSelectionPolicy(ctx.sessionProjections, target);
if (allowedModels === void 0) {
  const parentId = target.header.origin === "subagent" ? target.header.parentSession : void 0;
  if (parentId !== void 0) { /* inherit parent's policy — or its absence */ }
  else if (freshSession) { const current = settings.current(); allowedModels = current.enabled ? current.allowedModels : void 0; }
}

list_subagent_models and the provider/model schema fields are registered only when a policy exists (~L385-389, L412-425). This causes:

1. A resumed, imported or seeded session (session/end-seed, or firstLiveSeq > 0) never gets the policy, even though enabled: true is set.
2. A child of such a session inherits the absence of the policy and gets no settings fallback either.

Expected: a session that has no persisted policy falls back to settings.current() when enabled is true, whether or not it is fresh, and child sessions without a parent policy get the same fallback. The alternative is to at least surface a hint that model selection is inactive for this session.

Related, but not the same: #7168 (the allowlist is bypassed when provider/model are omitted) and #7421 (the subagent still uses the main model).

Workaround: start a new session instead of resuming one.