Gate --effort emission on per-model validity in Runner

Route normalization already enforces this on PATCH, but Runner is
public and constructed directly in tests/future call sites. Move the
"haiku gets no --effort, sonnet rejects xhigh" invariant down to
buildArgs so it survives any caller. When an invalid pair slips
through, log a warning and spawn without the flag.

Adds smoke coverage for haiku+xhigh and sonnet+xhigh.

Addresses Copilot review on PR #27.

https://claude.ai/code/session_015mACScqpz9U8NmhpDorPhA

Author: claude

src/server/runner.ts

@@ -14,6 +14,7 @@ import {
   DEFAULT_WALLCLOCK_CAP_MS,
   READ_ONLY_TOOLS,
   WRITE_TOOLS,
+  effortLevelsForModel,
   type Effort,
 } from '@shared/constants.js';
 import type { Mode } from '@shared/schemas/types.js';
@@ -423,8 +424,18 @@ export class Runner extends EventEmitter {
       'project',
       '--disable-slash-commands',
     ];
-    if (this.input.effort) {
+    // Last line of defence: only emit --effort if the value is valid for the
+    // model. The route layer already normalizes on PATCH, but Runner can be
+    // constructed directly (tests, future code paths), so the invariant
+    // "haiku never gets --effort, sonnet never gets xhigh" lives here too.
+    if (this.input.effort && effortLevelsForModel(this.input.model).includes(this.input.effort)) {
       args.push('--effort', this.input.effort);
+    } else if (this.input.effort) {
+      log.warn('runner.effort-dropped', {
+        model: this.input.model,
+        effort: this.input.effort,
+        hint: 'effort value not supported by model; spawning without --effort',
+      });
     }
     return args;
   }

test/runner.smoke.ts

@@ -1011,4 +1011,72 @@ await scenario('effort flag: omitted when null (haiku case)', async () => {
   });
 });
 
+await scenario('effort flag: dropped when model rejects the value (haiku + xhigh)', async () => {
+  await withSandbox(
+    'effort-haiku-xhigh',
+    async ({ runDir, projectDir, outputsDir, initialConfig }) => {
+      const dumpPath = join(runDir, 'argv.txt');
+      // Construct a malformed input: route normalization should have caught
+      // this, but Runner must defend itself when invoked directly.
+      initialConfig.effort = 'xhigh';
+      const runner = new Runner({
+        claudeBin: fakeBin,
+        projectDir,
+        runDir,
+        outputsDir,
+        prompt: 'go',
+        model: 'haiku',
+        effort: 'xhigh',
+        mode: 'read-only',
+        initialConfig,
+        env: {
+          ...process.env,
+          FAKE_CLAUDE_SCENARIO: 'happy',
+          FAKE_CLAUDE_DUMP_ARGS: dumpPath,
+        },
+      });
+      await runner.start();
+      const final = await runner.wait();
+      if (final.status !== 'completed') throw new Error(`expected completed, got ${final.status}`);
+      const argv = (await readFile(dumpPath, 'utf8')).split('\n');
+      if (argv.includes('--effort')) {
+        throw new Error(`expected no --effort for haiku, got: ${argv.join(' ')}`);
+      }
+    },
+  );
+});
+
+await scenario('effort flag: dropped when model rejects the value (sonnet + xhigh)', async () => {
+  await withSandbox(
+    'effort-sonnet-xhigh',
+    async ({ runDir, projectDir, outputsDir, initialConfig }) => {
+      const dumpPath = join(runDir, 'argv.txt');
+      initialConfig.effort = 'xhigh';
+      const runner = new Runner({
+        claudeBin: fakeBin,
+        projectDir,
+        runDir,
+        outputsDir,
+        prompt: 'go',
+        model: 'sonnet',
+        effort: 'xhigh', // xhigh is opus-only
+        mode: 'read-only',
+        initialConfig,
+        env: {
+          ...process.env,
+          FAKE_CLAUDE_SCENARIO: 'happy',
+          FAKE_CLAUDE_DUMP_ARGS: dumpPath,
+        },
+      });
+      await runner.start();
+      const final = await runner.wait();
+      if (final.status !== 'completed') throw new Error(`expected completed, got ${final.status}`);
+      const argv = (await readFile(dumpPath, 'utf8')).split('\n');
+      if (argv.includes('--effort')) {
+        throw new Error(`expected no --effort for sonnet+xhigh, got: ${argv.join(' ')}`);
+      }
+    },
+  );
+});
+
 console.log('\nAll runner smoke scenarios passed.');