Drop "Default" option from effort dropdown

The dropdown now lists only the model's actual levels and pre-selects
the model's default via the value attribute. onChange always patches
a real Effort (no more null path for opus/sonnet).

For legacy session.json files that were written before the effort
field existed (so it hydrated as null), runManager falls back to the
model's default at spawn time so the run never goes out without an
effort the UI showed as selected.

https://claude.ai/code/session_015mACScqpz9U8NmhpDorPhA

Author: claude

src/server/runManager.ts

@@ -13,6 +13,7 @@ import type { RunConfig, TranscriptFile } from '@shared/schemas/run.js';
 import type { NormalizedEvent, ServerSseEvent } from '@shared/schemas/events.js';
 import type { Mode, RunStatus } from '@shared/schemas/types.js';
 import type { ColumnConfig } from '@shared/schemas/session.js';
+import { defaultEffortForModel } from '@shared/constants.js';
 
 const SEQ_FILE = '.seq';
 const RING_BUFFER_LIMIT = 2_000;
@@ -316,7 +317,10 @@ export class RunManager extends EventEmitter {
       promptSha256: sha256(col.prompt),
       prompt: col.prompt,
       model: col.model,
-      effort: col.effort ?? null,
+      // Fall back to the model's default effort for legacy session.json files
+      // (written before this field existed) so a Run never goes out without
+      // an effort the UI showed as selected.
+      effort: col.effort ?? defaultEffortForModel(col.model),
       mode: sessionSnap.mode,
       status: 'preparing',
       startedAt: new Date().toISOString(),
@@ -338,7 +342,7 @@ export class RunManager extends EventEmitter {
       outputsDir: sandbox.outputsDir,
       prompt: col.prompt,
       model: col.model,
-      effort: col.effort ?? null,
+      effort: col.effort ?? defaultEffortForModel(col.model),
       mode: sessionSnap.mode as Mode,
       initialConfig,
     });

src/web/components/VariantColumn.tsx

@@ -147,16 +147,14 @@ export function VariantColumn(props: {
         {effortLevelsForModel(column.model).length > 0 && (
           <Hint content="Reasoning effort for the variant run">
             <select
-              value={column.effort ?? ''}
+              value={column.effort ?? (defaultEffortForModel(column.model) as Effort)}
               disabled={isLocked}
               onChange={(e) => {
-                const v = e.target.value;
                 void props.onPatchColumn(column.id, {
-                  effort: v === '' ? null : (v as Effort),
+                  effort: e.target.value as Effort,
                 });
               }}
             >
-              <option value="">Default</option>
               {effortLevelsForModel(column.model).map((x) => (
                 <option key={x} value={x}>
                   {EFFORT_LABELS[x]}