feat: establish unified administration and model context baseline

backend/src/routes/sessions.ts

@@ -383,6 +383,10 @@ export function sessionRoutes(
       question: string; name?: string; workspace?: string; workspaceId?: string;
       provider?: string; model?: string; thinking?: string;
     };
+    if ((b.provider === undefined) !== (b.model === undefined)
+      || (b.provider !== undefined && (typeof b.provider !== "string" || typeof b.model !== "string" || !b.provider || !b.model))) {
+      return reply.code(400).send({ error: "provider and model must be supplied together" });
+    }
     const principal = getPrincipal(req);
     let s: Settings;
     try { s = await d.getSettings(principal); } catch { return storageFailure(reply); }
@@ -446,11 +450,9 @@ export function sessionRoutes(
         }
       }
 	  const requestedCanonical = b.provider && b.model ? `${b.provider}/${b.model}` : undefined;
-	  let selectedCanonical = requestedCanonical ?? d.modelCatalog.defaultSession;
-	  let modelWarning: string | undefined;
-	  if (selectedCanonical && d.modelCatalog.defaultSession && !d.modelCatalog.hasSession(selectedCanonical)) {
-	    selectedCanonical = d.modelCatalog.defaultSession;
-	    modelWarning = `Configured model ${requestedCanonical ?? "selection"} is unavailable; using ${selectedCanonical}.`;
+	  const selectedCanonical = requestedCanonical ?? d.modelCatalog.defaultInteraction;
+	  if (selectedCanonical && d.modelCatalog.defaultInteraction && !d.modelCatalog.hasSession(selectedCanonical)) {
+	    return reply.code(503).send({ error: MODEL_UNAVAILABLE_MESSAGE, code: "model_unavailable" });
 	  }
 	  const selected = selectedCanonical ? splitCanonicalModelId(selectedCanonical) : undefined;
 	  const provider = selected?.provider ?? b.provider;
@@ -554,7 +556,7 @@ export function sessionRoutes(
         ),
         () => d.mgr.start(id, rt, runtimeOptions),
       );
-      return { id, ...(modelWarning ? { warning: modelWarning } : {}) };
+      return { id };
     } finally {
       if (revisionLease && !manifestPersisted) {
         await revisionLease.abort().catch((error: unknown) => {
@@ -680,10 +682,17 @@ export function sessionRoutes(
         provider?: string; model?: string; thinking?: string;
         workspace_id?: string; workspace_revision?: string;
       };
-	  const savedCanonical = saved.provider && saved.model ? `${saved.provider}/${saved.model}` : "";
-	  if (d.modelCatalog.defaultSession && (!savedCanonical || !d.modelCatalog.hasSession(savedCanonical))) {
+	  const requested = (req.body ?? {}) as { provider?: string; model?: string; thinking?: string };
+	  if ((requested.provider === undefined) !== (requested.model === undefined)
+	    || (requested.provider !== undefined && (typeof requested.provider !== "string" || typeof requested.model !== "string" || !requested.provider || !requested.model))) {
+	    return reply.code(400).send({ error: "provider and model must be supplied together" });
+	  }
+	  const selectedCanonical = requested.provider && requested.model
+	    ? `${requested.provider}/${requested.model}` : d.modelCatalog.defaultInteraction;
+	  if (d.modelCatalog.defaultInteraction && (!selectedCanonical || !d.modelCatalog.hasSession(selectedCanonical))) {
 	    return reply.code(503).send({ error: MODEL_UNAVAILABLE_MESSAGE, code: "model_unavailable" });
 	  }
+	  const selected = selectedCanonical ? splitCanonicalModelId(selectedCanonical) : saved;
       let workspaceConfigPath: string;
       let workspaceDescriptor: WorkspaceDescriptor | undefined;
       try {
@@ -716,7 +725,7 @@ export function sessionRoutes(
       if (existing) {
         const state = existing.bridge.turnState();
         if (state === "running" || state === "waiting") {
-          return reply.code(200).send({ id, alreadyActive: true });
+          return reply.code(200).send({ id, alreadyActive: true, workspaceId: saved.workspace_id });
         }
       }
       const ensure = await d.readiness.ensure(
@@ -727,8 +736,8 @@ export function sessionRoutes(
         ...(ensure.code ? { code: ensure.code } : {}),
       });
       const options = {
-        provider: saved?.provider,
-        model: saved?.model,
+        provider: selected.provider,
+        model: selected.model,
         thinking: saved?.thinking ?? settings.thinking,
         author: principal.displayName ?? principal.subject,
         principal,
@@ -750,7 +759,7 @@ export function sessionRoutes(
       if (current) {
         const state = current.bridge.turnState();
         if (state === "running" || state === "waiting") {
-          return reply.code(200).send({ id, alreadyActive: true });
+          return reply.code(200).send({ id, alreadyActive: true, workspaceId: saved.workspace_id });
         }
       }
 
@@ -791,7 +800,7 @@ export function sessionRoutes(
         d.mgr.configure(rt, runtimeOptions), null,
         () => d.mgr.start(id, rt, runtimeOptions),
       );
-      return reply.code(200).send({ id, alreadyActive: false });
+      return reply.code(200).send({ id, alreadyActive: false, workspaceId: saved.workspace_id });
     });
   });
   app.post("/sessions/:id/close", async (req, reply) => {

backend/src/routes/settings.ts

@@ -16,8 +16,8 @@ export function effectiveSettings(
   modelCatalog?: RuntimeModelCatalog,
 ): Settings {
   const workspaces = listWorkspaces(cfg.harnessDir);
-  const selected = modelCatalog?.defaultSession
-    ? splitCanonicalModelId(modelCatalog.defaultSession)
+  const selected = modelCatalog?.defaultInteraction
+    ? splitCanonicalModelId(modelCatalog.defaultInteraction)
     : undefined;
   return {
     workspace: stored.workspace ?? workspaces[0]?.name,