diff --git a/src/node/services/workflows/WorkflowActionRunner.test.ts b/src/node/services/workflows/WorkflowActionRunner.test.ts
index 3cdb4b61f6..afdcafb721 100644
--- a/src/node/services/workflows/WorkflowActionRunner.test.ts
+++ b/src/node/services/workflows/WorkflowActionRunner.test.ts
@@ -202,6 +202,67 @@ describe("WorkflowActionRunner", () => {
     });
   });
 
+  test("keeps ctx.exec output out of action diagnostics", async () => {
+    using tmp = new DisposableTempDir("workflow-action-exec-diagnostics");
+    const sourcePath = path.join(tmp.path, "exec-diagnostics.js");
+    const source = `
+      module.exports.metadata = { version: 1, description: "Exec diagnostics", effect: "read" };
+      module.exports.execute = async (_input, ctx) => {
+        console.log("action log");
+        const result = await ctx.exec(process.execPath, ["-e", "process.stdout.write('cmd stdout'); process.stderr.write('cmd stderr')"]);
+        return { stdout: result.stdout, stderr: result.stderr, exitCode: result.exitCode };
+      };
+    `;
+    await fs.writeFile(sourcePath, source, "utf-8");
+    const runner = new WorkflowActionRunner();
+
+    const result = await runner.execute(createAction(sourcePath, source), {
+      input: null,
+      cwd: tmp.path,
+      timeoutMs: 10_000,
+      artifactDir: path.join(tmp.path, "artifacts"),
+    });
+
+    expect(result.output).toEqual({ stdout: "cmd stdout", stderr: "cmd stderr", exitCode: 0 });
+    expect(result.stdout).toBe("action log\n");
+    expect(result.stderr).toBe("");
+  });
+
+  test("keeps cleanup ps warnings out of action diagnostics", async () => {
+    if (process.platform === "win32") {
+      return;
+    }
+    using tmp = new DisposableTempDir("workflow-action-ps-diagnostics");
+    const fakeBinDir = path.join(tmp.path, "bin");
+    const fakePsPath = path.join(fakeBinDir, "ps");
+    const sourcePath = path.join(tmp.path, "ps-diagnostics.js");
+    const sentinel = "fake ps warning should stay hidden";
+    await fs.mkdir(fakeBinDir, { recursive: true });
+    await fs.writeFile(fakePsPath, `#!/bin/sh\nprintf '${sentinel}\\n' >&2\n`, "utf-8");
+    await fs.chmod(fakePsPath, 0o755);
+    const source = `
+      module.exports.metadata = { version: 1, description: "Ps diagnostics", effect: "read" };
+      module.exports.execute = async (_input, ctx) => {
+        process.env.PATH = ${JSON.stringify(fakeBinDir + path.delimiter)} + (process.env.PATH || "");
+        const result = await ctx.exec(process.execPath, ["-e", ""]);
+        return { exitCode: result.exitCode };
+      };
+    `;
+    await fs.writeFile(sourcePath, source, "utf-8");
+    const runner = new WorkflowActionRunner();
+
+    const result = await runner.execute(createAction(sourcePath, source), {
+      input: null,
+      cwd: tmp.path,
+      timeoutMs: 10_000,
+      artifactDir: path.join(tmp.path, "artifacts"),
+    });
+
+    expect(result.output).toEqual({ exitCode: 0 });
+    expect(result.stderr).not.toContain(sentinel);
+    expect(result.stderr).toBe("");
+  });
+
   test("built-in git actions reject truncated command output", async () => {
     using tmp = new DisposableTempDir("workflow-action-git-truncated");
     const repoRoot = path.join(tmp.path, "repo");
diff --git a/src/node/services/workflows/WorkflowActionRunner.ts b/src/node/services/workflows/WorkflowActionRunner.ts
index 34925724e2..d32d176169 100644
--- a/src/node/services/workflows/WorkflowActionRunner.ts
+++ b/src/node/services/workflows/WorkflowActionRunner.ts
@@ -992,7 +992,10 @@ function captureResult(capture) {
 
 function listChildPids(pid) {
   try {
-    return execFileSync("ps", ["-axo", "pid=,ppid="], { encoding: "utf-8" })
+    return execFileSync("ps", ["-axo", "pid=,ppid="], {
+      encoding: "utf-8",
+      stdio: ["ignore", "pipe", "ignore"],
+    })
       .trim()
       .split(/\n+/)
       .map((line) => line.trim().split(/\s+/).map((value) => Number(value)))
@@ -1328,11 +1331,9 @@ async function execCommand(command, args = [], options = {}) {
   timer?.unref?.();
   child.stdout?.on("data", (chunk) => {
     appendCapture(stdout, chunk);
-    process.stdout.write(chunk);
   });
   child.stderr?.on("data", (chunk) => {
     appendCapture(stderr, chunk);
-    process.stderr.write(chunk);
   });
   child.on("exit", (code, childSignal) => {
     exitCode = code;
diff --git a/src/node/services/workflows/WorkflowRunner.test.ts b/src/node/services/workflows/WorkflowRunner.test.ts
index 24215f9d00..4a07caa09e 100644
--- a/src/node/services/workflows/WorkflowRunner.test.ts
+++ b/src/node/services/workflows/WorkflowRunner.test.ts
@@ -1806,6 +1806,9 @@ describe("WorkflowRunner", () => {
     expect(parsed.ignored).toContain("ignored.txt");
     expect(parsed.branchFiles).toContain("feature.txt");
     expect(parsed.branchDiff).toContain("feature.txt");
+    expect(parsed.branchDiff).toContain("diff --git");
+    expect(parsed.branchDiff).toContain("+feature");
+    expect(parsed.branchStat).not.toContain("diff --git");
     expect(parsed.unstagedDiff).toContain("+dirty");
     expect(parsed.diffTruncated).toEqual({ branch: false, staged: false, unstaged: false });
     expect(parsed.branchStat).toContain("feature.txt");