fix(cli): preserve first line of channels logs at window boundary (#84106)

BSG2000 · Copilot · clawsweeper[bot] · web-flow · commit b7ba7c3f2a1e · 2026-05-19T13:27:43.000Z
Summary: - The PR updates `openclaw channels logs` tail-window reading to keep a complete first line when the 1 MB window starts on a newline boundary, adds a regression test, and adds a changelog entry. - Reproducibility: yes. Source inspection on current main shows the unconditional first-line drop, and the PR ... s provide terminal before/after CLI output for a 2 MB log whose tail window starts exactly after a newline. Automerge notes: - PR branch already contained follow-up commit before automerge: Merge remote-tracking branch 'origin/main' into fix/channels-logs-dro… - PR branch already contained follow-up commit before automerge: fix(cli): preserve first line of channels logs at window boundary Validation: - ClawSweeper review passed for head 284b312. - Required merge gates passed before the squash merge. Prepared head SHA: 284b312 Review: #84106 (comment) Co-authored-by: BSG2000 <bsg2000@users.noreply.github.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: clawsweeper <274271284+clawsweeper[bot]@users.noreply.github.com> Co-authored-by: clawsweeper[bot] <274271284+clawsweeper[bot]@users.noreply.github.com> Approved-by: takhoffman Co-authored-by: takhoffman <781889+takhoffman@users.noreply.github.com>
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -10,6 +10,7 @@ Docs: https://docs.openclaw.ai
 
 ### Fixes
 
+- CLI/channels: preserve the first line of `openclaw channels logs` output when the rolling tail window starts exactly on a line boundary, mirroring the already-fixed `readLogSlice` behavior in `src/logging/log-tail.ts`.
 - Control UI: treat terminal session status as authoritative over stale active-run flags so completed terminal runs stop showing abort/live UI. (#84057)
 - CLI: preserve embedded equals signs in inline root option values instead of truncating after the second separator. (#83995) Thanks @ThiagoCAltoe.
 - Matrix/config: accept `messages.queue.byChannel.matrix` queue overrides and keep queue provider schema/type keys aligned for Matrix, Google Chat, and Mattermost. Thanks @bdjben.
diff --git a/src/commands/channels.logs.test.ts b/src/commands/channels.logs.test.ts
@@ -141,6 +141,65 @@ describe("channelsLogsCommand", () => {
     expect(payload.lines.map((line) => line.message)).toEqual(["current sent"]);
   });
 
+  it("returns the first line of the tail window when start aligns with a line boundary", async () => {
+    // MAX_BYTES in readTailLines is 1_000_000. We build a file of 2_000_000 bytes
+    // made of 10_000 lines each exactly 200 bytes (199 payload + "\n"), so the
+    // read window starts at byte offset 1_000_000 which is exactly on a line
+    // boundary (byte 999_999 is the trailing "\n" of the previous line).
+    // Without checking the byte before the window, readTailLines drops line 5000 silently.
+    const LINE_SIZE = 200;
+    const TOTAL_LINES = 10_000;
+    const FIRST_INDEX = 5000; // first line of the tail window after alignment
+
+    const buildLine = (message: string) => {
+      const base = logLine({
+        module: "gateway/channels/slack/send",
+        message,
+      });
+      const payloadLen = LINE_SIZE - 1; // reserve 1 byte for newline
+      // Re-emit with a padded message so total byte length is constant.
+      const padNeeded = payloadLen - Buffer.byteLength(base);
+      if (padNeeded < 0) {
+        throw new Error(`base log line too long: ${Buffer.byteLength(base)} > ${payloadLen}`);
+      }
+      const padded = logLine({
+        module: "gateway/channels/slack/send",
+        message: message + " ".repeat(padNeeded),
+      });
+      if (Buffer.byteLength(padded) !== payloadLen) {
+        throw new Error(`padded line wrong size: ${Buffer.byteLength(padded)} vs ${payloadLen}`);
+      }
+      return padded + "\n";
+    };
+
+    const handle = await fs.open(logPath, "w");
+    try {
+      for (let i = 0; i < TOTAL_LINES; i++) {
+        let message: string;
+        if (i === FIRST_INDEX) {
+          message = "first-line-in-window";
+        } else if (i === TOTAL_LINES - 1) {
+          message = "last-line";
+        } else {
+          message = "filler";
+        }
+        await handle.write(buildLine(message));
+      }
+    } finally {
+      await handle.close();
+    }
+
+    await channelsLogsCommand(
+      { channel: "slack", json: true, lines: String(TOTAL_LINES) },
+      runtime,
+    );
+
+    const payload = readJsonPayload();
+    const messages = payload.lines.map((line) => line.message.trimEnd());
+    expect(messages[0]).toBe("first-line-in-window");
+    expect(messages[messages.length - 1]).toBe("last-line");
+  });
+
   it("does not fall back to rolling logs for a missing custom log file", async () => {
     const configuredFile = path.join(tempDir, "custom-channel.log");
     const fallbackFile = path.join(tempDir, "openclaw-2026-04-25.log");
diff --git a/src/commands/channels/logs.ts b/src/commands/channels/logs.ts
@@ -63,6 +63,12 @@ async function readTailLines(file: string, limit: number): Promise<string[]> {
   const start = Math.max(0, size - MAX_BYTES);
   const handle = await fs.open(file, "r");
   try {
+    let prefix = "";
+    if (start > 0) {
+      const prefixBuf = Buffer.alloc(1);
+      const prefixRead = await handle.read(prefixBuf, 0, 1, start - 1);
+      prefix = prefixBuf.toString("utf8", 0, prefixRead.bytesRead);
+    }
     const length = Math.max(0, size - start);
     if (length === 0) {
       return [];
@@ -71,7 +77,7 @@ async function readTailLines(file: string, limit: number): Promise<string[]> {
     const readResult = await handle.read(buffer, 0, length, start);
     const text = buffer.toString("utf8", 0, readResult.bytesRead);
     let lines = text.split("\n");
-    if (start > 0) {
+    if (start > 0 && prefix !== "\n") {
       lines = lines.slice(1);
     }
     if (lines.length && lines[lines.length - 1] === "") {
