fix: deliver harness prompts off argv

packages/cli/src/cli-impl.ts

@@ -68,7 +68,8 @@ import {
   injectClaudeAgentRelayMcpConfig,
   injectCodexSubcommandArgs,
   resolveAgentRelayBrokerMcpArgs,
-  resolveRelayMcpFromEnv as resolveRelayMcpFromEnvShared
+  resolveRelayMcpFromEnv as resolveRelayMcpFromEnvShared,
+  spawnNonInteractiveAndCapture
 } from '@agentworkforce/runtime';
 import {
   listBuiltInPersonas,
@@ -4502,50 +4503,16 @@ async function runPersonaImprover(args: {
   const timeoutMs = selection.harnessSettings.timeoutSeconds
     ? selection.harnessSettings.timeoutSeconds * 1000
     : undefined;
-  let captureResult: { exitCode: number | null; stderr: string };
+  let captureResult: { exitCode: number; stderr: string };
   try {
-    captureResult = await new Promise<{ exitCode: number | null; stderr: string }>(
-      (resolveResult) => {
-        const child = spawn(spec.bin, [...spec.args], {
-          cwd,
-          env: childEnv,
-          stdio: ['ignore', 'pipe', 'pipe'],
-          shell: false
-        });
-        let stderrBuf = '';
-        let forceKillTimeout: NodeJS.Timeout | undefined;
-        child.stdout?.setEncoding('utf8');
-        child.stderr?.setEncoding('utf8');
-        child.stderr?.on('data', (chunk: string) => {
-          stderrBuf += chunk;
-        });
-        // SIGTERM first; if the harness traps or ignores it, escalate to
-        // SIGKILL after a 1s grace so the timeout is actually enforced.
-        const timeout =
-          timeoutMs !== undefined
-            ? setTimeout(() => {
-                child.kill('SIGTERM');
-                forceKillTimeout = setTimeout(() => {
-                  if (!child.killed) child.kill('SIGKILL');
-                }, 1000);
-              }, timeoutMs)
-            : undefined;
-        const clearTimers = () => {
-          if (timeout) clearTimeout(timeout);
-          if (forceKillTimeout) clearTimeout(forceKillTimeout);
-        };
-        child.on('error', (err) => {
-          clearTimers();
-          resolveResult({ exitCode: 1, stderr: `${stderrBuf}${err.message}\n` });
-        });
-        child.on('close', (code, signal) => {
-          clearTimers();
-          const exitCode =
-            typeof code === 'number' ? code : signal ? signalExitCode(signal) : null;
-          resolveResult({ exitCode, stderr: stderrBuf });
-        });
-      }
-    );
+    captureResult = await spawnNonInteractiveAndCapture({
+      bin: spec.bin,
+      args: [...spec.args],
+      prompt: spec.prompt,
+      cwd,
+      env: childEnv,
+      ...(timeoutMs !== undefined ? { timeoutMs } : {})
+    });
   } finally {
     // Always restore — a synchronous spawn() throw or unexpected promise
     // rejection must not leave orphaned `opencode.json` (or any other
@@ -4554,7 +4521,7 @@ async function runPersonaImprover(args: {
   }
   if (captureResult.exitCode !== 0) {
     throw new Error(
-      `improver exited with code=${captureResult.exitCode ?? 'null'}.${captureResult.stderr ? ` stderr: ${captureResult.stderr.slice(0, 400)}` : ''}`
+      `improver exited with code=${captureResult.exitCode}.${captureResult.stderr ? ` stderr: ${captureResult.stderr.slice(0, 400)}` : ''}`
     );
   }
   let raw: string;

packages/persona-kit/CHANGELOG.md

@@ -7,6 +7,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Breaking Changes
+
+- `buildNonInteractiveSpec` no longer includes the one-shot task in `args`.
+  Consumers must deliver the new required `prompt` descriptor through stdin or
+  a prompt file as directed; spawning only `bin` and `args` now omits the task.
+
+### Fixed
+
+- Keep large one-shot harness prompts off argv to avoid Linux
+  `MAX_ARG_STRLEN`/`E2BIG` failures.
+
 ## [4.1.23] - 2026-07-15
 
 ### Added

packages/persona-kit/src/index.ts

@@ -227,6 +227,7 @@ export {
   type BuildInteractiveSpecInput,
   type InteractiveConfigFile,
   type InteractiveSpec,
+  type NonInteractivePrompt,
   type NonInteractiveSpec,
   type RelayMcpConfig,
   resolvePersonaRelayMcp,

packages/persona-kit/src/interactive-spec.test.ts

@@ -343,9 +343,9 @@ test('opencode non-interactive spec omits cwd/model flags and normalizes the age
     '--format',
     'default',
     '--title',
-    'daily-ship',
-    'say pong'
+    'daily-ship'
   ]);
+  assert.deepEqual(result.prompt, { mode: 'stdin', contents: 'say pong' });
   assert.ok(!result.args.includes('--dir'));
   assert.ok(!result.args.includes('--model'));
 
@@ -413,7 +413,7 @@ test('grok warns for unsupported permission fields', () => {
   ]);
 });
 
-test('grok non-interactive spec uses single-shot mode with cwd and always-approve', () => {
+test('grok non-interactive spec uses a prompt file with cwd and always-approve', () => {
   const result = buildNonInteractiveSpec({
     harness: 'grok',
     personaId: 'daily-ship',
@@ -432,10 +432,13 @@ test('grok non-interactive spec uses single-shot mode with cwd and always-approv
     'plain',
     '--cwd',
     '/tmp/project',
-    '--always-approve',
-    '--single',
-    'Reply pong.\n\nUser task:\nsay pong'
+    '--always-approve'
   ]);
+  assert.deepEqual(result.prompt, {
+    mode: 'file',
+    contents: 'Reply pong.\n\nUser task:\nsay pong',
+    flag: '--prompt-file'
+  });
   assert.deepEqual(result.configFiles, [
     { path: 'AGENTS.md', contents: 'Reply pong.\n' }
   ]);
@@ -458,10 +461,13 @@ test('grok non-interactive spec still adds always-approve for unsupported permis
     'grok-build-0.1',
     '--output-format',
     'plain',
-    '--always-approve',
-    '--single',
-    'say pong'
+    '--always-approve'
   ]);
+  assert.deepEqual(result.prompt, {
+    mode: 'file',
+    contents: 'say pong',
+    flag: '--prompt-file'
+  });
   assert.deepEqual(result.warnings, [
     'persona declares permissions.mode "plan" but the grok harness only supports bypassPermissions via --always-approve; proceeding with Grok defaults.'
   ]);
@@ -534,7 +540,44 @@ test('claude non-interactive spec omits unsupported --name while preserving run
   assert.equal(args[outputIdx + 1], 'text');
   assert.ok(promptIdx >= 0);
   assert.equal(args[promptIdx + 1], 'Reply pong.');
-  assert.equal(args[args.length - 1], 'say pong');
+  assert.ok(!args.includes('say pong'));
+  assert.deepEqual(result.prompt, { mode: 'stdin', contents: 'say pong' });
+});
+
+test('non-interactive tasks stay off argv and argv remains below Linux per-argument limits', () => {
+  const marker = 'TASK_CANARY_d7e9b9b0';
+  const task = `${marker}\n${'x'.repeat(200_000)}`;
+  const cases = [
+    { harness: 'claude' as const, model: 'claude-sonnet-4-6', promptMode: 'stdin' },
+    { harness: 'codex' as const, model: 'openai-codex/gpt-5.3-codex', promptMode: 'stdin' },
+    { harness: 'opencode' as const, model: 'opencode/minimax-m2.5', promptMode: 'stdin' },
+    { harness: 'grok' as const, model: 'grok-build-0.1', promptMode: 'file' }
+  ];
+
+  for (const entry of cases) {
+    const result = buildNonInteractiveSpec({
+      harness: entry.harness,
+      personaId: 'argv-budget-test',
+      model: entry.model,
+      systemPrompt: 'short system prompt',
+      task,
+      name: 'argv-budget-test',
+      workingDirectory: '/tmp/project'
+    });
+    const argvBytes = [result.bin, ...result.args].reduce(
+      (total, arg) => total + Buffer.byteLength(arg) + 1,
+      0
+    );
+    const largestArgBytes = Math.max(...result.args.map((arg) => Buffer.byteLength(arg)));
+
+    assert.equal(result.prompt.mode, entry.promptMode, entry.harness);
+    assert.ok(result.prompt.contents.includes(marker), entry.harness);
+    assert.ok(result.args.every((arg) => !arg.includes(marker)), entry.harness);
+    // Linux rejects any single argv element at 128 KiB (MAX_ARG_STRLEN),
+    // independently of the larger combined argv + env budget.
+    assert.ok(largestArgBytes < 128 * 1024, `${entry.harness}: largest arg=${largestArgBytes}`);
+    assert.ok(argvBytes < 128 * 1024, `${entry.harness}: argv total=${argvBytes}`);
+  }
 });
 
 test('opencode omits agent.prompt when systemPrompt is empty', () => {

packages/persona-kit/src/interactive-spec.ts

@@ -662,28 +662,42 @@ export function buildInteractiveSpec(input: BuildInteractiveSpecInput): Interact
   }
 }
 
+/** Off-argv delivery for a one-shot harness prompt. Keeping the potentially
+ * large per-run task out of `args` avoids Linux's 128 KiB single-argument
+ * limit as well as the combined argv + env limit. */
+export type NonInteractivePrompt =
+  | { readonly mode: 'stdin'; readonly contents: string }
+  | {
+      readonly mode: 'file';
+      readonly contents: string;
+      readonly flag: '--prompt-file';
+    };
+
 /** Result of translating a persona's runtime into a one-shot, non-interactive
- * spawnable command. Caller writes `configFiles` before spawning. */
+ * spawnable command. Caller writes `configFiles` and delivers `prompt` using
+ * its declared off-argv mode before spawning. */
 export interface NonInteractiveSpec {
   bin: string;
   args: readonly string[];
+  prompt: NonInteractivePrompt;
   configFiles: readonly InteractiveConfigFile[];
   warnings: readonly string[];
 }
 
 /**
  * Translate a persona's runtime into a non-interactive, one-shot command.
  * Layers harness-specific non-interactive flags on top of {@link buildInteractiveSpec},
- * then appends the user task. Pure — no I/O.
+ * then declares how the caller must deliver the user task off argv. Pure — no I/O.
  *
- * - `claude`: appends `--print --output-format text <task>`.
- * - `codex`:  prefixes `exec`, appends `--skip-git-repo-check`, then a prompt
- *   built from any `initialPrompt` joined with the user task.
+ * - `claude`: appends `--print --output-format text`; task is written to stdin.
+ * - `codex`:  prefixes `exec`, appends `--skip-git-repo-check -`; stdin receives
+ *   a prompt built from any `initialPrompt` joined with the user task.
  * - `opencode`: prefixes `run`, appends `--format default
- *   [--title <n>] <task>`; model selection stays in the generated agent config.
+ *   [--title <n>]`; task is written to stdin and model selection stays in the
+ *   generated agent config.
  * - `grok`: appends `--output-format plain [--cwd <cwd>] --always-approve
- *   --single <prompt>`, where prompt includes the persona system prompt plus
- *   the one-shot task.
+ *   --prompt-file <temp-path>` at spawn time, where the temporary file contains
+ *   the persona system prompt plus the one-shot task.
  */
 export function buildNonInteractiveSpec(
   input: BuildInteractiveSpecInput & {
@@ -696,10 +710,10 @@ export function buildNonInteractiveSpec(
   switch (input.harness) {
     case 'claude': {
       const args = [...interactive.args, '--print', '--output-format', 'text'];
-      args.push(input.task);
       return {
         bin: interactive.bin,
         args,
+        prompt: { mode: 'stdin', contents: input.task },
         configFiles: interactive.configFiles,
         warnings: interactive.warnings
       };
@@ -710,7 +724,8 @@ export function buildNonInteractiveSpec(
         : input.task;
       return {
         bin: interactive.bin,
-        args: ['exec', ...interactive.args, '--skip-git-repo-check', prompt],
+        args: ['exec', ...interactive.args, '--skip-git-repo-check', '-'],
+        prompt: { mode: 'stdin', contents: prompt },
         configFiles: interactive.configFiles,
         warnings: interactive.warnings
       };
@@ -723,10 +738,10 @@ export function buildNonInteractiveSpec(
       // separately, and `opencode run` does not support `--dir`.
       const args = ['run', ...interactive.args, '--format', 'default'];
       if (input.name) args.push('--title', input.name);
-      args.push(input.task);
       return {
         bin: interactive.bin,
         args,
+        prompt: { mode: 'stdin', contents: input.task },
         configFiles: interactive.configFiles,
         warnings: interactive.warnings
       };
@@ -740,10 +755,10 @@ export function buildNonInteractiveSpec(
       if (!args.includes('--always-approve')) {
         args.push('--always-approve');
       }
-      args.push('--single', prompt);
       return {
         bin: interactive.bin,
         args,
+        prompt: { mode: 'file', contents: prompt, flag: '--prompt-file' },
         configFiles: interactive.configFiles,
         warnings: interactive.warnings
       };

packages/runtime/CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Deliver one-shot Claude, Codex, and OpenCode prompts through stdin and Grok
+  prompts through a private temporary file instead of oversized argv elements.
+
 ## [4.1.24] - 2026-07-16
 
 ### Fixed