Fix wave chunk 2: thinking levels auto-populate everywhere; legacy records show the resolved level

- thinking-default.ts: defaultOrderLevel (the ordering's first supported,
  the client twin of the server's defaultThinkingLevel) + populateLevel
  (an explicit level always rides; the WRITE clamps server-side, bd68486,
  and the cross-surface signal re-reads the clamped truth; only absence
  populates from the ordering) + THINKING_LABEL shared.
- Setup dialog (item 5): per-slot thinking selectors pre-populated with
  the default-order level per picked model, editable; disabled until the
  model pick; prefillLevelFromPin keeps a stored level as-is and populates
  legacy pins from the ordering.
- Composer + agent section (item 6): fresh model picks always write a
  level: the stored one rides, absence populates; the unset state can
  never re-enter. Item 4: records with a model but no stored level display
  the RESOLVED level (ordering's first supported) instead of a dash, in
  the composer pill and the settings slot triggers/menus.
- Item 7 verified live end-to-end: an explicit level rides into the PUT,
  the server clamps, the signal re-reads, the pill shows the clamped truth.

tests/byok-refusal.test.ts

@@ -1,7 +1,7 @@
 import { describe, it } from "node:test";
 import assert from "node:assert/strict";
 import { parseModelsRefusal } from "../components/chat.tsx";
-import { prefillFromSlots, setupStage } from "../components/setup-dialog.tsx";
+import { prefillFromSlots, prefillLevelFromPin, setupStage } from "../components/setup-dialog.tsx";
 import { isModelsRefusal, modelsNotConfigured } from "../src/core/settings.ts";
 import type { ModelCatalogEntry, ModelSlotName } from "../src/core/index.ts";
 
@@ -90,6 +90,24 @@ describe("prefillFromSlots — the SetupDialog prefill (BYOK wave)", () => {
 	});
 });
 
+describe("prefillLevelFromPin — the setup dialog's level prefill (chunk 2)", () => {
+	const entry = (levels: string[]) =>
+		({ id: "m", name: "M", provider: "p", reasoning: true, input: ["text"], supportedLevels: levels, cost: { input: 1, output: 1, cacheRead: 0, cacheWrite: 0 }, contextWindow: 1000, maxTokens: 1000 }) as never;
+
+	it("a stored level the pinned model still supports prefills as-is", () => {
+		assert.equal(prefillLevelFromPin(entry(["low", "high"]), { thinkingLevel: "high" }), "high");
+	});
+
+	it("a stored level the model LOST rides as-is — Save clamps server-side (bd68486)", () => {
+		assert.equal(prefillLevelFromPin(entry(["minimal", "medium"]), { thinkingLevel: "xhigh" }), "xhigh");
+	});
+
+	it("a legacy pin with no stored level prefills the ordering's level", () => {
+		assert.equal(prefillLevelFromPin(entry(["low", "medium"]), {}), "medium");
+		assert.equal(prefillLevelFromPin(entry(["low", "medium"]), null), "medium");
+	});
+});
+
 describe("setupStage — unchanged by the BYOK wave", () => {
 	it("keys first (owner ordering), pickers when a provider is keyed", () => {
 		assert.equal(setupStage(null), "keys");