fix(harness): preserve adapter text output bytes (#797)

packages/harness/src/first-output.mjs

@@ -51,7 +51,7 @@ export function modelEventStream({ harness, runDir }) {
         const last = event.messages?.at(-1);
         if (last?.role === 'assistant') {
           failed = ['error', 'aborted'].includes(last.stopReason);
-          answer = (last.content ?? []).filter(part => part.type === 'text').map(part => part.text).join('\n');
+          answer = (last.content ?? []).filter(part => part.type === 'text').map(part => part.text + '\n').join('');
         }
       }
     } else {
@@ -60,7 +60,7 @@ export function modelEventStream({ harness, runDir }) {
       const block = event.type === 'stream_event' && event.event?.type === 'content_block_start' && event.event.content_block;
       if (block?.type === 'tool_use' && typeof block.id === 'string' && block.id.length && typeof block.name === 'string' && block.name.length) mark('output');
       if (block && [["text", block.text], ["thinking", block.thinking]].some(([type, value]) => block.type === type && typeof value === 'string' && value.length)) mark('output');
-      if (event.type === 'result') { failed = event.is_error === true || event.subtype !== 'success'; answer = event.result ?? ''; }
+      if (event.type === 'result') { failed = event.is_error === true || event.subtype !== 'success'; answer = event.result ?? ''; if (typeof answer === 'string' && !answer.endsWith('\n')) answer += '\n'; }
     }
   };
   return {
@@ -93,7 +93,7 @@ if (process.argv[1] && resolve(process.argv[1]) === fileURLToPath(import.meta.ur
   child.on('error', () => { bad = true; });
   child.on('close', (code, signal) => {
     if (bad || signal || code !== 0) { process.exitCode = code || 1; return; }
-    try { const answer = stream.finish(); if (answer) process.stdout.write(answer + '\n'); }
+    try { process.stdout.write(stream.finish()); }
     catch { process.stderr.write('model event stream failed\n'); process.exitCode = 1; }
   });
 }

packages/harness/src/runner.mjs

@@ -392,7 +392,9 @@ function runTurn({ session, request, n, env, onChild }) {
   const markOutput = firstOutputMarker(session.runDir);
   child.stdout.setEncoding("utf8");
   child.stdout.on("data", (s) => {
-    markOutput(s);
+    // Empty text blocks can render only newlines; they are not model output.
+    // Preserve the stdout fallback for content emitted by a managed adapter.
+    if (!session.proxyFirstTurn || !['pi', 'claude-code'].includes(session.harness) || /[^\n]/.test(s)) markOutput(s);
     if (out.length < 4 * BODY_MAX) out += s;
   });
   return new Promise((resolve) => {

packages/harness/tests/model-stream.test.mjs

@@ -29,7 +29,7 @@ for (const harness of ['pi', 'claude']) {
     send(delta);
     assert.equal(fs.readFileSync(file, 'utf8'), 'output\n');
     send(harness === 'pi' ? {type:'agent_end',messages:[{role:'assistant',stopReason:'stop',content:[{type:'text',text:'final answer'}]}]} : {type:'result',subtype:'success',result:'final answer'});
-    assert.equal(stream.finish(), 'final answer');
+    assert.equal(stream.finish(), 'final answer\n');
   });
   test(`${harness} does not mark empty deltas, pings, or startup events`, t => {
     const root = fs.mkdtempSync(join(tmpdir(), 'stream797-'));
@@ -51,20 +51,37 @@ test('monitor forwards only the answer and keeps model events private', async t
   const child = spawn(process.execPath, [monitor, 'pi', root, process.execPath, '-e', producer], { stdio:['ignore','pipe','pipe'] });
   let stdout='', stderr=''; child.stdout.on('data', c => stdout += c); child.stderr.on('data', c => stderr += c);
   const code = await new Promise(resolve => child.on('close', resolve));
-  assert.equal(code, 0, stderr); assert.equal(stdout.trim(), 'answer');
+  assert.equal(code, 0, stderr); assert.equal(stdout, 'answer\n');
   assert.equal(fs.readFileSync(join(root, 'proxy-first-output'), 'utf8'), 'output\n');
 });
 
-test('an empty final answer does not create synthetic stdout or a marker', async t => {
-  const { spawn } = await import('node:child_process');
-  const { fileURLToPath } = await import('node:url');
-  const root = fs.mkdtempSync(join(tmpdir(), 'stream797-empty-'));
-  t.after(() => fs.rmSync(root, { recursive: true, force: true }));
-  const monitor = fileURLToPath(new URL('../src/first-output.mjs', import.meta.url));
-  const producer = `console.log(JSON.stringify({type:'result',subtype:'success',result:''}))`;
-  const child = spawn(process.execPath, [monitor, 'claude', root, process.execPath, '-e', producer], { stdio:['ignore','pipe','pipe'] });
-  let stdout=''; child.stdout.on('data', c => stdout += c);
-  const code = await new Promise(resolve => child.on('close', resolve));
-  assert.equal(code, 0); assert.equal(stdout, '');
-  assert.equal(fs.existsSync(join(root, 'proxy-first-output')), false);
-});
+// Expected bytes come from the adapters' base text modes: Pi prints each text
+// block with a newline; Claude terminates its result only if needed.
+for (const [harness, parts, expected] of [
+  ['pi', ['Plain answer.'], 'Plain answer.\n'],
+  ['pi', ['Line one\n雪 👩🏽‍💻 café\nLine three'], 'Line one\n雪 👩🏽‍💻 café\nLine three\n'],
+  ['pi', ['Line one\n雪 👩🏽‍💻 café\nLine three\n'], 'Line one\n雪 👩🏽‍💻 café\nLine three\n\n'],
+  ['pi', [], ''], ['pi', [''], '\n'],
+  ['pi', [null], ''], ['pi', ['First block.', 'Second block.\nUnicode 雪'], 'First block.\nSecond block.\nUnicode 雪\n'],
+  ['claude', ['Plain answer.'], 'Plain answer.\n'],
+  ['claude', ['Line one\n雪 👩🏽‍💻 café\nLine three'], 'Line one\n雪 👩🏽‍💻 café\nLine three\n'],
+  ['claude', ['Line one\n雪 👩🏽‍💻 café\nLine three\n'], 'Line one\n雪 👩🏽‍💻 café\nLine three\n'],
+  ['claude', [], '\n'], ['claude', [null], '\n'],
+  ['claude', ['First block.', 'Second block.\nUnicode 雪'], 'Second block.\nUnicode 雪\n'],
+]) {
+  test(`${harness} preserves base stdout bytes for ${JSON.stringify(parts)}`, async t => {
+    const { spawn } = await import('node:child_process');
+    const { fileURLToPath } = await import('node:url');
+    const root = fs.mkdtempSync(join(tmpdir(), 'stream797-parity-'));
+    t.after(() => fs.rmSync(root, { recursive: true, force: true }));
+    const monitor = fileURLToPath(new URL('../src/first-output.mjs', import.meta.url));
+    const event = harness === 'pi'
+      ? {type:'agent_end',messages:[{role:'assistant',stopReason:'stop',content:parts.map(text => text === null ? {type:'toolCall',id:'t',name:'read'} : {type:'text',text})}]}
+      : {type:'result',subtype:'success',result:parts.filter(x => x !== null).at(-1) ?? ''};
+    const child = spawn(process.execPath, [monitor, harness, root, process.execPath, '-e', `console.log(${JSON.stringify(JSON.stringify(event))})`], {stdio:['ignore','pipe','pipe']});
+    const chunks=[]; let stderr=''; child.stdout.on('data', c => chunks.push(c)); child.stderr.on('data', c => stderr += c);
+    const code = await new Promise(resolve => child.on('close', resolve));
+    assert.equal(code, 0, stderr); assert.deepEqual(Buffer.concat(chunks), Buffer.from(expected));
+    assert.equal(fs.existsSync(join(root, 'proxy-first-output')), false);
+  });
+}

packages/harness/tests/runner.test.mjs

@@ -228,6 +228,19 @@ test("a message becomes a turn, the answer goes back as a RESULT, SIGTERM releas
   assert.ok(!existsSync(join(ctx.runDir, "tools.sock")));
 });
 
+test("managed empty answer formatting does not mark model output", async t => {
+  const ctx = await setup(t, {session: {proxyFirstTurn: true, turnEnd: "exit"}});
+  writeFileSync(join(ctx.runDir, "proxy-first-turn-enabled"), "enabled\n");
+  writeFileSync(join(ctx.dir, "adapter.sh"), "printf '\\n\\n'\n");
+  ctx.inbox = [];
+  const r = startRunner(ctx.runDir, ctx.cap);
+  t.after(() => r.child.kill("SIGKILL"));
+  await until(() => ctx.store.get("SELECT 1 FROM role_claims WHERE role='coder' AND op='claim'"));
+  const sent = ctx.call(ctx.pm, "message.send", {to:"coder", body:"empty", class:"REQUEST"});
+  await until(() => ctx.store.get("SELECT 1 FROM deliveries WHERE message=? AND op='read'", sent.id));
+  assert.equal(existsSync(join(ctx.runDir, "proxy-first-output")), false);
+});
+
 // Row 109 (#1603): each turn reads the state when it starts. The fake adapter echoes the request,
 // so a reply shows the block the turn was given.
 const ask = async (ctx, body = "what now") => {