feat(models): BYOK all the way down — factory pins deleted, per-need refusal gates

Owner decision 2026-09-22: 'it doesn't make sense to have any default
model configured anywhere; the application is bring your own keys.'

config.ts: MODELS deleted; ModelRole becomes an explicit 9-role union;
DEFAULT_THINKING_ORDER (medium, low, high, minimal, xhigh, max) bakes
the unset-level default — first entry the model supports; explicitly
set levels keep pi's native nearest-clamp.

core/settings-resolution: the factory layer dissolves — the chain is
role override → slot → NOTHING. resolveSettings(record) takes no
factory. Empty chains resolve to null/undefined; a thinkingLevel-only
slot is inert (stored, never run). resolveConversationSpec: chat.model
override over the strong slot, null when both empty. resolveRoleSpec
spans all nine roles for the job/extraction engines.

Refusal envelope (core/settings.ts): modelsNotConfigured(missing) —
{error, code: 'models_not_configured', missing: [slot tiers]} +
ModelsNotConfiguredError with .envelope. Per-need gates, each honest:
- chat-handler: universal turn gate (new + continuing turns) returns
  503 before beginTurn — no liveness, no write-ahead persist, no graph
  trigger before the gate fires.
- runner.runJob: unresolvable engine lands the job as error with the
  envelope wording; no phantom loop, no result steer.
- extraction: refuseIfStagesUnconfigured throws before any stage
  (turn-service info-skips so coverage retries next turn; the import
  route surfaces per-file code+missing); labeler-less runs skip
  cluster naming with a console line and still merge.

Write side: slot entries must carry a model — level-only slot writes
are 400s (absent slot key = clear). piEngineForSpec resolves unset
thinking levels via DEFAULT_THINKING_ORDER; piEngineFor now throws
honestly; thinkingLevelFor/modelIdFor deleted; teacher-agent, pi-run,
visual-maker, pdf-reader all read engine.level.

model-catalog: defaults/slots/rolePins null when the chain is empty
(contracts nullable) — no phantom ids in payloads. Stores drop
MODEL_PINS entirely.

Tests: pin-leaners converted to explicit injection (per-chat model
pins on scripted chats — exactly what the setup flow writes; faux
engines for agent-construction tests). New coverage: the 503 gate
envelope, the runner refusal, the extraction refusal + labeler skip.

Gates: typecheck, lint, 815/815, build.

src/server/settings-body.ts

@@ -309,11 +309,14 @@ export function parseModelsSettingsBody(body: unknown): SettingsBodyResult<Model
 		}
 		const parsed = parseRoleOverride(raw[key], key);
 		if (!parsed.ok) return { ok: false, error: parsed.error };
-		if (Object.keys(parsed.override).length) {
-			settings[key as (typeof MODEL_SLOTS)[number]] = parsed.override;
-		} else {
-			return { ok: false, error: `slot "${key}" must set model or thinkingLevel (absent slot = unset)` };
+		// BYOK (owner, 2026-09-22): a slot IS a model choice — no factory
+		// floor exists, so a thinkingLevel alone can never run; every slot
+		// write must carry the model (the level is an optional rider). An
+		// absent slot key clears the tier (replace-whole section).
+		if (!parsed.override.model) {
+			return { ok: false, error: `slot "${key}" must set a model (thinkingLevel alone cannot run — absent slot = unset)` };
 		}
+		settings[key as (typeof MODEL_SLOTS)[number]] = parsed.override;
 	}
 	return { ok: true, settings };
 }